Analysis of the characteristics of phosphine production by anaerobic digestion based on microbial community dynamics, metabolic pathways, and isolation of the phosphate-reducing strain

Although phosphine is ubiquitously present in anaerobic environments, little is known regarding the microbial community dynamics and metabolic pathways associated with phosphine formation in an anaerobic digestion system. This study investigated the production of phosphine in anaerobic digestion, with results indicating that phosphine production mainly occurred during logarithmic microbial growth. Dehydrogenase and hydrogen promoted the production of phosphine, with a maximum phosphine concentration of 300 mg/m³. The abundance of Ruminococcaceae and Escherichia was observed to promote phosphine generation. The analysis of metabolic pathways based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) and the MetaCyc pathway database revealed the highest relative abundance of replication and repair in genetic information processing; further, the cofactor, prosthetic group, electron carrier, and vitamin biosynthesis were observed to be closely related to phosphine formation. A phylogenetic tree was reconstructed based on the neighbor-joining method. The results indicated the clear evolutionary position of the isolated Pseudescherichia sp. SFM4 strain, adjacent to Escherichia, with a stable phosphate-reducing ability for a maximum phosphine concentration of 26 mg/m³. The response surface experiment indicated that the initial optimal conditions for phosphine production by SFM4 could be achieved with nitrogen, carbon, and phosphorus loads of 6.17, 300, and 10 mg/L, respectively, at pH 7.47. These results provide comprehensive insights into the dynamic changes in the microbial structure, isolated single bacterial strain, and metabolic pathways associated with phosphine formation. They also provide information on the molecular biology associated with phosphorus recycling.

Phosphine-Activated Lysine Analogues for Fast Chemical Control of Protein Subcellular Localization and Protein SUMOylation

The Staudinger reduction and its variants have exceptional compatibility with live cells but can be limited by slow kinetics. Herein we report new small-molecule triggers that turn on proteins through a Staudinger reduction/self-immolation cascade with substantially improved kinetics and yields. We achieved this through site-specific incorporation of a new set of azidobenzyloxycarbonyl lysine derivatives in mammalian cells. This approach allowed us to activate proteins by adding a nontoxic, bioorthogonal phosphine trigger. We applied this methodology to control a post-translational modification (SUMOylation) in live cells, using native modification machinery. This work significantly improves the rate, yield, and tunability of the Staudinger reduction-based activation, paving the way for its application in other proteins and organisms.

New environmental model for thermodynamic ecology of biological phosphine production

We present a new model for the biological production of phosphine (PH₃). Phosphine is found globally, in trace amounts, in the Earth's atmosphere. It has been suggested as a key molecule in the phosphorus cycle, linking atmospheric, lithospheric and biological phosphorus chemistry. Phosphine's production is strongly associated with marshes, swamps and other sites of anaerobic biology. However the mechanism of phosphine's biological production has remained controversial, because it has been believed that reduction of phosphate to phosphine is endergonic. In this paper we show through thermodynamic calculations that, in specific environments, the combined action of phosphate reducing and phosphite disproportionating bacteria can produce phosphine. Phosphate-reducing bacteria can capture energy from the reduction of phosphate to phosphite through coupling phosphate reduction to NADH oxidation. Our hypothesis describes how the phosphate chemistry in an environmental niche is coupled to phosphite generation in ground water, which in turn is coupled to the phosphine production in water and atmosphere, driven by a specific microbial ecology. Our hypothesis provides clear predictions on specific complex environments where biological phosphine production could be widespread. We propose tests of our hypothesis in fieldwork.

Stabilization of Aliphatic Phosphines by Auxiliary Phosphine Sulfides Offers Zeptomolar Affinity and Unprecedented Selectivity for Probing Biological CuI

Full elucidation of the functions and homeostatic pathways of biological copper requires tools that can selectively recognize and manipulate this trace nutrient within living cells and tissues, where it exists primarily as CuI . Buffered at attomolar concentrations, intracellular CuI is, however, not readily accessible to commonly employed amine and thioether-based chelators. Herein, we reveal a chelator design strategy in which phosphine sulfides aid in CuI coordination while simultaneously stabilizing aliphatic phosphine donors, producing a charge-neutral ligand with low-zeptomolar dissociation constant and 1017 -fold selectivity for CuI over ZnII , FeII , and MnII . As illustrated by reversing ATP7A trafficking in cells and blocking long-term potentiation of neurons in mouse hippocampal brain tissue, the ligand is capable of intercepting copper-dependent processes. The phosphine sulfide-stabilized phosphine (PSP) design approach, which confers resistance towards protonation, dioxygen, and disulfides, could be readily expanded towards ligands and probes with tailored properties for exploring CuI in a broad range of biological systems.

Dermal uptake and percutaneous penetration of organophosphate esters in a human skin ex vivo model

Organophosphate esters (OPEs) are used as flame retardants, plasticizers, and as hydraulic fluids. They are present in indoor environments in high concentrations compared with other flame retardants, and human exposure is ubiquitous. In this study we provide data for estimating dermal uptake for eight OPEs and ranking in OPEs risk assessment. Dermal uptake and percutaneous penetration of the OPEs were studied in a Franz diffusion cell system using human skin dosed with a mixture of OPEs in an ethanol:toluene (4:1) solution. Large variation in penetration profiles was observed between the OPEs. The chlorinated OPEs tris(2-chloroisopropyl) phosphate (TCIPP), and in particular tris(2-chloroethyl) phosphate (TCEP), penetrated the skin quite rapidly while tris(1,3-dichlor-2-propyl) phosphate (TDCIPP) and triphenyl phosphate (TPHP) tended to build up in the skin tissue and only smaller amounts permeated through the skin. For tris(isobutyl) phosphate (TIBP), tris(n-butyl) phosphate (TNBP), and tris(methylphenyl) phosphate (TMPP) the mass balance was not stable over time indicating possible degradation during the experimental period of 72 h. The rates at which OPEs permeated through the skin decreased in the order TCEP > TCIPP ≥ TBOEP > TIBP ≥ TNBP > TDCIPP > TPHP > TMPP. Generally, the permeation coefficient, k_p, decreased with increasing log K_ow, whereas lag time and skin deposition increased with log K_ow. The present data indicate that dermal uptake is a non-negligible human exposure pathway for the majority of the studied OPEs.

Fresh red blood cells transfusion protects against aluminum phosphide-induced metabolic acidosis and mortality in rats

BACKGROUND

Aluminum phosphide (AlP) is used as pesticide in some countries for protection of stored grains. Human poisoning with AlP due to suicide attempt or accidental environmental exposure is associated with very high mortality partially due to development of severe metabolic acidosis. Previous studies have shown that hemoglobin has high buffering capacity and erythrocytes can potentially be used for management of metabolic acidosis. The aim of this study was to evaluate the effect of fresh packed red blood cells (RBC) transfusion on survival and cardiovascular function in AlP-poisoned rats.

METHODOLOGY/PRINCIPAL FINDINGS

Rats were poisoned with AlP by gavage. Fresh packed RBC was transfused via tail vein after AlP administration. Acid-base balance, vital signs and mortality was assessed and compared in experimental groups. Infusion of fresh packed RBC (1.5 ml) one hour after AlP (4-15 mg/kg) intoxication was associated with a significant decrease in mortality rate. Packed RBC infusion improved blood pH, HCO3-, Na+ and Ca2+ levels. Plasma troponin level was also reduced and ECG changes were reversed following packed RBC infusion in AlP intoxicated rats.

CONCLUSIONS

Our results showed that fresh RBC transfusion could ameliorate metabolic acidosis and enhance survival in AlP-poisoned rat. We assume that an increase in pool of RBCs may modulate acid-base balance or potentially chelate AlP-related toxic intermediates via phosphine-hemoglobin interaction.

Effects of applied potential on phosphine formation in synthetic wastewater treatment by Microbial Electrolysis Cell (MEC)

Phosphine (PH₃) emission from conventional biological wastewater treatment is very inefficient (ng-μg m^-3). In this work, we investigated the feasibility of promoting PH₃ formation from inorganic phosphorus (IP) or organic phosphorus (OP) containing synthetic wastewater treatment by Microbial Electrolysis Cell (MEC) for the first time. Positive effect of applied potential on PH₃ production was observed after methanogens was inhibited. The highest production of PH₃ (1103.10 ± 72.02 ng m^-3) was obtained in IP-fed MEC operated at -0.6 V, which was about 5-fold and 2-fold compared to that in open circuit experiment and OP-fed MEC, respectively. Meanwhile, PH₃ formation corresponded positively with current density and alkaline phosphatase activity. This result showed that suitable potential could enhance the activity of relevant enzymes and boost the biosynthesis of PH₃. Bacterial communities analysis based on high-throughput sequencing revealed that applied potential was conductive to the enrichment of phosphate-reducing organisms in contrast to the control test. These results provide a new idea for resource utilization of phosphorus in wastewater.

The combination of in silico and in vivo approaches for the investigation of disrupting effects of tris (2-chloroethyl) phosphate (TCEP) toward core receptors of zebrafish

Tris (2-chloroethyl) phosphate (TCEP), a substitute for brominated flame retardants (FRs) that have been phased out of use, is frequently detected in aqueous environments. However, previous studies on its endocrine disrupting effects have mainly focused on terrestrial mammals. Here, to comprehensively evaluate the potential adverse effects of TCEP on aquatic vertebrates, zebrafish was used as a model to examine developmental phenotypes. The underlying mechanisms of toxicity of TCEP were further explored using in silico and in vivo approaches. In vivo results demonstrated morphologic changes and mortalities of zebrafish when exposed to high concentrations (14,250 and 28,500 μg TCEP/L). In silico results showed that TCEP can bind to and interact with nuclear receptors with different patterns. The combination of in vivo and in silico analyses indicated that receptors can influence each other at the molecular level and that ER, ThR, RXR and RyR were the key receptors influencing the transcriptional pathways. Our results demonstrate that TCEP has adverse effects at relatively low concentrations by affecting key receptors and genes of vertebrates. These results exhibited the need for further studies to evaluate the potential health risks of TCEP to human infants/children due to its high concentration in Chinese rivers (up to 3700 ng/L) and potential for human exposure.

A new method and tool for detection and quantification of PM oxidative potential

Airborne particulate matter (PM) contains several quinones, which are able to generate reactive oxygen species impacting on cell viability. A method able to detect and quantify PM oxidative potential, based on the cytochrome c (cyt-c) reduction by means of superoxide anion produced through quinones redox cycling in the presence of reducing agents, is here described. Tris(2-carboxyethyl)phosphine resulted to be the most efficient reducing agent among the ones tested. The procedure included rapid particles extraction, followed by two alternative analytical methods, a spectrophotometric assay based on the initial rate of cyt-c reduction at 550 nm, and an amperometric assay, based on self-assembled monolayers modified gold electrodes. The smallest amount of PM needed to obtain an evaluable signal is 2 μg. The described procedure may represent a starting point to develop devices for PM measurements in polluted atmospheric environments.

Electrospray ionization multi-stage mass spectrometric study of the interaction products of the cytotoxic complex [Cu(thp)₄][PF₆] with methionine-rich model peptides

RATIONALE

The cytotoxic activity of the copper(I) complex [Cu(thp)4][PF6] (CP) (thp = tris(hydroxymethyl) phosphine) is correlated with its high accumulation in cancer cells. Human copper transporter 1 (hCtr1) has been described as the main trans-membrane protein involved in cellular trafficking of physiological copper. Methionine-rich peptide sequences incorporated in the extracellular domain of hCtr1 play a key role in the cellular internalization of copper. We wish to investigate the interaction of CP with model peptides that mimic the extracellular domain of hCtr1.

METHODS

The interaction of CP with methionine-rich and methionine-free model peptides has been investigated by electrospray ionization mass spectrometry and the interaction products have been characterized by multiple collisional experiments, using an ion trap mass instrument.

RESULTS

The interaction of CP with selected methionine-rich model peptides, Ac-MMMMPMTFK-NH2 (P1) and Ac-MGMSYMDSK-NH2 (P2), shows that the native copper complex, after sequential loss of phosphines, induces the formation of [Cu(P1)(thp)](+) and [Cu(P1/P2)](+) adducts reasonably by inclusion of the Cu(I) ion in the peptide framework. Collisionally induced fragmentations (MS(n)) of [Cu(P1/P2)](+) give evidence that the metal is coordinated by the thioether-S of two adjacent methionine residues. Interaction of the same peptides with the isostructural complex [Ag(thp)4](+) or AgNO3 yields similar experimental evidence, leading to [Ag(P1/P2)](+).

CONCLUSIONS

Methionine sequences incorporated in model peptides are crucial for the recruitment of copper from CP. Such a metal-peptide interaction does not take place when methionine-free Ac-NleGNleSYNleDSK-NH2 (P3) is utilized. A mechanism for tumor cell internalization of CP involving: (i) chemically driven sequential loss of phosphines from the native tetrahedral complex, followed by (ii) transfer of Cu(I) to the methionine-rich sequences typical of the hCtr1 transporter, is proposed.

A selective phosphine-based fluorescent probe for nitroxyl in living cells

A novel fluorescein-based fluorescent probe for nitroxyl (HNO) based on the reductive Staudinger ligation of HNO with an aromatic phosphine was prepared. This probe reacts with HNO derived from Angeli's salt and 4-bromo Piloty's acid under physiological conditions without interference by other biological redox species. Confocal microscopy demonstrates this probe detects HNO by fluorescence in HeLa cells and mass spectrometric analysis of cell lysates confirms this probe detects HNO following the proposed mechanism.

Alveolar epithelial dynamics in postpneumonectomy lung growth

The intimate anatomic and functional relationship between epithelial cells and endothelial cells within the alveolus suggests the likelihood of a coordinated response during postpneumonectomy lung growth. To define the population dynamics and potential contribution of alveolar epithelial cells to alveolar angiogenesis, we studied alveolar Type II and I cells during the 21 days after pneumonectomy. Alveolar Type II cells were defined and isolated by flow cytometry using a CD45(-) , MHC class II(+) , phosphine(+) phenotype. These phenotypically defined alveolar Type II cells demonstrated an increase in cell number after pneumonectomy; the increase in cell number preceded the increase in Type I (T1α(+) ) cells. Using a parabiotic wild type/GFP pneumonectomy model, <3% of the Type II cells and 1% of the Type I cells were positive for GFP-a finding consistent with the absence of a blood-borne contribution to alveolar epithelial cells. The CD45(-) , MHC class II(+) , phosphine(+) Type II cells demonstrated the active transcription of angiogenesis-related genes both before and after pneumonectomy. When the Type II cells on Day 7 after pneumonectomy were compared to nonsurgical controls, 10 genes demonstrated significantly increased expression (P<0.05). In contrast to the normal adult Type II cells, there was notable expression of inflammation-associated genes (Ccl2, Cxcl2, Ifng) as well as genes associated with epithelial growth (Ereg, Lep). Together, the data suggest an active contribution of local alveolar Type II cells to alveolar growth.

Methylation of arsenic by recombinant human wild-type arsenic (+3 oxidation state) methyltransferase and its methionine 287 threonine (M287T) polymorph: Role of glutathione

Arsenic (+3 oxidation state) methyltransferase (AS3MT) is the key enzyme in the pathway for methylation of arsenicals. A common polymorphism in the AS3MT gene that replaces a threonyl residue in position 287 with a methionyl residue (AS3MT/M287T) occurs at a frequency of about 10% among populations worldwide. Here, we compared catalytic properties of recombinant human wild-type (wt) AS3MT and AS3MT/M287T in reaction mixtures containing S-adenosylmethionine, arsenite (iAs(III)) or methylarsonous acid (MAs(III)) as substrates and endogenous or synthetic reductants, including glutathione (GSH), a thioredoxin reductase (TR)/thioredoxin (Trx)/NADPH reducing system, or tris (2-carboxyethyl) phosphine hydrochloride (TCEP). With either TR/Trx/NADPH or TCEP, wtAS3MT or AS3MT/M287T catalyzed conversion of iAs(III) to MAs(III), methylarsonic acid (MAs(V)), dimethylarsinous acid (DMAs(III)), and dimethylarsinic acid (DMAs(V)); MAs(III) was converted to DMAs(III) and DMAs(V). Although neither enzyme required GSH to support methylation of iAs(III) or MAs(III), addition of 1mM GSH decreased K(m) and increased V(max) estimates for either substrate in reaction mixtures containing TR/Trx/NADPH. Without GSH, V(max) and K(m) values were significantly lower for AS3MT/M287T than for wtAS3MT. In the presence of 1mM GSH, significantly more DMAs(III) was produced from iAs(III) in reactions catalyzed by the M287T variant than in wtAS3MT-catalyzed reactions. Thus, 1mM GSH modulates AS3MT activity, increasing both methylation rates and yield of DMAs(III). AS3MT genotype exemplified by differences in regulation of wtAS3MT and AS3MT/M287T-catalyzed reactions by GSH may contribute to differences in the phenotype for arsenic methylation and, ultimately, to differences in the disease susceptibility in individuals chronically exposed to inorganic arsenic.

A ratiometric fluorescent probe for assessing mitochondrial phospholipid peroxidation within living cells

Mitochondrial oxidative damage contributes to a wide range of pathologies, and lipid peroxidation of the mitochondrial inner membrane is a major component of this disruption. However, despite its importance, there are no methods to assess mitochondrial lipid peroxidation within cells specifically. To address this unmet need we have developed a ratiometric, fluorescent, mitochondria-targeted lipid peroxidation probe, MitoPerOx. This compound is derived from the C11-BODIPY(581/591) probe, which contains a boron dipyromethane difluoride (BODIPY) fluorophore conjugated via a dienyl link to a phenyl group. In response to lipid peroxidation the fluorescence emission maximum shifts from ∼590 to ∼520nm. To target this probe to the matrix-facing surface of the mitochondrial inner membrane we attached a triphenylphosphonium lipophilic cation, which leads to its selective uptake into mitochondria in cells, driven by the mitochondrial membrane potential. Here we report on the development and characterization of MitoPerOx. We found that MitoPerOx was taken up very rapidly into mitochondria within cells, where it responded to changes in mitochondrial lipid peroxidation that could be measured by fluorimetry, confocal microscopy, and epifluorescence live cell imaging. Importantly, the peroxidation-sensitive change in fluorescence at 520nm relative to that at 590nm enabled the use of the probe as a ratiometric fluorescent probe, greatly facilitating assessment of mitochondrial lipid peroxidation in cells.

Exploring the smallest active fragment of HsQSOX1b and finding a highly efficient oxidative engine

Human quiescin-sulfhydryl oxidase 1 isoform b (HsQSOX1b) is a highly efficient, multiple-domain enzyme that directly inserts disulfide bonds into client protein. However, previous studies have focused mainly on the catalytic activity of the whole protein rather than its domain structure. In this research, we dissected the structure and function of HsQSOX1b and explored its mechanism as a highly efficient sulfhydryl oxidase by analyzing the truncated variants. The results showed that the first HsQSOX1b thioredoxin domain was essential for thiol oxidase activity. The smallest active fragment (SAQ) was identified to consist of a helix-rich region (HRR) and an essential for respiration and viability/augmenter of liver regeneration (ERV/ALR) domain, which remained highly active to oxidize an artificial non-thiol substrate but not small molecular and protein thiols. Our study clearly demonstrated that SAQ is a highly efficient oxidative engine, which shows high efficiency in the de novo disulfide formation and oxygen reduction and that this more efficient oxidative engine is necessary for the highly efficient catalysis of QSOXs compared to Erv1 and Erv2. This study will help address the roles of different HsQSOX1b domains in de novo disulfide formation and encourage the engineering of more efficient QSOX variants for the in vitro folding of disulfide-containing proteins.

Titanocene-phosphine derivatives as precursors to cytotoxic heterometallic TiAu2 and TiM (M = Pd, Pt) compounds. Studies of their interactions with DNA

A series of tri- and bimetallic titanium-gold, titanium-palladium, and titanium-platinum derivatives of the general formulas [Ti{η(5)-C(5)H(4)(CH(2))(n)PPh(2)(AuCl)}(2)]·2THF [n = 0 (1); n = 2 (2); n = 3 (3)] and [TiCl(2){η(5)-C(5)H(4)κ-(CH(2))(n)PPh(2)}(2)(MCl(2))]·2THF [M = Pd, n = 0 (4); n = 2 (5); n = 3 (6) ; M = Pt, n = 0 (7); n = 2 (8); n = 3 (9)] have been synthesized and characterized by different spectroscopic techniques and mass spectrometry. The molecular structures of compounds 1-9 have been investigated by means of density functional theory calculations. The calculated IR spectra of the optimized structures fit well with the experimental IR data obtained for 1-9. The stability of the heterometallic compounds in deuterated solvents [CDCl(3), dimethyl sulfoxide (DMSO)-d(6), and mixtures 50:50 DMSO-d(6)/D(2)O and 1:99 DMSO-d(6)/D(2)O at acidic and neutral pH] has been evaluated by (31)P and (1)H NMR spectroscopy showing a higher stability for these compounds than for Cp(2)TiCl(2) or precursors [Ti{η(5)-C(5)H(4)(CH(2))(n)PPh(2)}(2)]. The new compounds display a lower acidity (1-2 units) than Cp(2)TiCl(2). The decomposition products have been identified over time. Complexes 1-9 have been tested as potential anticancer agents, and their cytotoxicity properties were evaluated in vitro against HeLa human cervical carcinoma and DU-145 human prostate cancer cells. TiAu(2) and TiPd compounds were highly cytotoxic for these two cell lines. The interactions of the compounds with calf thymus DNA have been evaluated by thermal denaturation (1-9) and by circular dichroism (1, 3, 4, and 7) spectroscopic methods. All of these complexes show a stronger interaction with DNA than that displayed by Cp(2)TiCl(2) at neutral pH. The data are consistent with electrostatic interactions with DNA for TiAu(2) compounds and for a covalent binding mode for TiM (M = Pd, Pt) complexes.

Cell-permeable Ln(III) chelate-functionalized InP quantum dots as multimodal imaging agents

Quantum dots (QDs) are ideal scaffolds for the development of multimodal imaging agents, but their application in clinical diagnostics is limited by the toxicity of classical CdSe QDs. A new bimodal MRI/optical nanosized contrast agent with high gadolinium payload has been prepared through direct covalent attachment of up to 80 Gd(III) chelates on fluorescent nontoxic InP/ZnS QDs. It shows a high relaxivity of 900 mM(-1) s(-1) (13 mM(-1 )s(-1) per Gd ion) at 35 MHz (0.81 T) and 298 K, while the bright luminescence of the QDs is preserved. Eu(III) and Tb(III) chelates were also successfully grafted to the InP/ZnS QDs. The absence of energy transfer between the QD and lanthanide emitting centers results in a multicolor system. Using this convenient direct grafting strategy additional targeting ligands can be included on the QD. Here a cell-penetrating peptide has been co-grafted in a one-pot reaction to afford a cell-permeable multimodal multimeric MRI contrast agent that reports cellular localization by fluorescence and provides high relaxivity and increased tissue retention with respect to commercial contrast agents.

Efficacy and attractiveness of zinc phosphide bait in common voles (Microtus arvalis)

BACKGROUND

Minimising the concentration of active ingredient in rodenticide bait is desirable economically and for the protection of the agroecosystem. This study aimed to identify a zinc phosphide concentration that balances palatability and efficacy for common vole (Microtus arvalis Pall.) management and to compare the attractiveness of two bait carriers.

RESULTS

Bait uptake of voles was reduced by 87-98% compared with plain bait when bait contained 0.4-3.2% zinc phosphide. There was an almost 50% decrease in the uptake of zinc phosphide when the zinc phosphide concentration of bait was doubled. Red dye used in commercially available bait decreased bait consumption by 10%. Daily consumption of zinc phosphide bait on days 2 to 5 was half the consumption on the first day of exposure. In bait choice tests, wheat kernels were preferred initially, but within 12 h similar amounts of wheat-based pellets and wheat kernels were eaten.

CONCLUSIONS

According to the results from the laboratory trial, a zinc phosphide concentration of 2.1% seemed to balance uptake/efficacy best and may be most appropriate for the management of common vole populations. This concentration is substantially lower than the concentration used in many registered products. A reduced concentration of active ingredient and the use of pellet bait instead of wheat which is highly attractive for birds may have advantages for agroecosystem health when applying zinc phosphide for rodent control.

Coupling of Metal Containing Homing Devices to Liposomes via a Maleimide Linker: Use of TCEP to Stabilize Thiol-groups without Scavenging Metals

Liposomes for drug delivery are often prepared with maleimide groups on the distal end of PEG to enable coupling of homing devices, such as antibodies, or other proteins. EDTA is used to stabilize the thiol group in the homing device for attachment to the maleimide. However, when using a homing device that contains a metal, EDTA inactivates this by scavenging of the metal. Holo-transferrin (Tf) containing two iron atoms (Fe(3+)), has a much higher affinity for the Tf receptor than apo-Tf (which does not contain any Fe(3+)). To couple Tf to a liposome, the introduction of a thiol group is necessary. During this process, by using N-succinimidyl S-acetylthioacetate (SATA), followed by 2-3 h coupling to the liposomes, Fe(3+) is scavenged by EDTA. This causes a decreased affinity of Tf for its receptor, resulting in a decreased targeting efficiency of the liposomes. Tris(2-carboxyethyl)phosphine (TCEP) hydrochloride is a sulfhydryl reductant that is often used in protein biochemistry. We found that TCEP (0.01 mM) does not scavenge Fe(3+) from Tf and is able to protect thiol groups for the coupling to maleimide. Furthermore, TCEP does not interfere with the maleimide coupling itself. In this communication, we describe the preparation of liposomes, focussing on the coupling of Tf to the maleimide linker at the distal end of PEG, without loosing Fe(3+) from Tf. This method can be applied to other metal-containing homing devices as well.

Preliminary investigation on the role of microorganisms in the production of phosphine

The relationships between the phosphine content and various microbial populations, activities of different enzymes were investigated firstly. The results indicated that the phosphine content of samples from various environments was positively related to total anaerobic microorganisms, organic phosphate compound-dissolving bacteria, denitrifying bacteria, and the activities of alkaline phosphatase and dehydrogenase, with correlation coefficients (R2) up to 0.93, 0.90, 0.69, 0.79, and 0.82, respectively. Results also showed that the phosphine content was not related to total aerobic microorganisms, inorganic phosphate compound-dissolving bacteria, sulfate-reducing bacteria, and the acidic phosphatase activity. Nutrients such as yeast extract and glucose were added, at a time and individually, to normal or autoclaved soil samples. The soil samples were inoculated with sulfate-reducing bacterial (SRB) enrichments and/or denitrifying bacterial (DNB) enrichment. After incubation for one month at 30 degrees C, the phosphane content of these samples was analyzed. The results indicated that the addition of glucose or yeast extract could greatly increase the phosphane content. Moreover, it was revealed that inoculation with SRB or DNB could also promote the formation of phosphine. The DNB, however, was more efficient in this regard. The highest phosphine content, about 5 times that of the control, was detected in the sample that was added with both glucose and yeast extract and inoculated with SRB and DNB simultaneously. SRB and DNB were enriched for several generations and the phosphane content of different generations was analyzed. Furthermore, SRB and DNB enrichments were inoculated into different media, in the beginning of enriching, the phosphane content was about the same for different enrichments, and differed more significantly as the enrichment process was carried further. In fourth generation, the phosphane content of DNB enrichment was about 3 times of that of SRB enrichment, indicating that the inoculation of different enrichments into different media caused the variations of the phosphine content. The highest phosphine content was detected in the sample which was inoculated with DNB enrichment into the denitrifying medium without nitrate. It is inferred from these results that microorganisms play an important role in the production of phosphine in different environments.

Measuring degradation of zinc phosphide residues in possum stomach contents

Zinc phosphide (ZnP) has been identified as a potentially cost-effective vertebrate pesticide for possum (Trichosurus vulpecula) control in New Zealand. We established methodology for analysis of microencapsulated ZnP formulations (MZP) and investigated the half-life of residual ZnP in the stomach contents of poisoned possums. An interlaboratory study was conducted to compare results of ZnP analysis in stomach contents. The half-life of ZnP was 3.4 days for ZnP in possum stomach contents and 6.7 days in vomit. Subsequent estimates were made of 34 and 67 days, respectively, for residual ZnP to decline to concentrations below the 1 microg/g method detection limit.

[Relationships between phosphine content of samples and their microbial populations and enzyme activities]

The relationships between phosphine content and various microbial florae, activities of different enzymes were investigated. The results indicated that the phosphine content of samples from various environments was positively related to total anaerobic microorganisms, organic phosphate compounds-dissolving bacteria, denitrifying bacteria, alkaline phosphatase activity and dehydrogenase activity of the samples. The correlation coefficients (R2) for these were 0.93, 0.90, 0.69, 0.79 and 0.82, respectively. The results also showed that the phosphine content was not related to total aerobic microorganisms, inorganic phosphate compounds-dissolving bacteria, sulfate-reducing bacteria, acidic phosphatase activity. In addition to formerly results, the results might infer that the formation of phosphine was due to the reduction of organic phosphate compounds by anaerobic heterotrophic microbes, especially the denitrifying bacteria by using reducing sugar.

Template-Assisted Ligand Encapsulation; the Impact of an Unusual Coordination Geometry on a Supramolecular Pyridylphosphine−Zn(II)porphyrin Assembly

The tris(para-pyridyl)phosphine template (1) has been used in conjunction with a series of meso-substituted Zn(II)-tetraphenylporphyrins complexes (2-10) to create supramolecular encapsulated ligand assemblies via Zn-N(pyr) interactions. The structural features of supramolecular ligand 1.[2](3) have been investigated in detail using X-ray crystallography, NMR specroscopy, and UV-vis spectroscopy. The pyridylphosphine-porphyrin stoichiometry determined in solution (1:3) differs markedly with that observed in the solid state (2:5, for assembly [1](2).[2](5)). The difference originates from an unusual coordination behavior of one of the Zn centers, which is octahedrally surrounded through double axial coordination by the pyridyl groups of the two different molecules of 1.

In vivo antiarrhythmic and cardiac electrophysiologic effects of a novel diphenylphosphine oxide IKur blocker (2-isopropyl-5-methylcyclohexyl) diphenylphosphine oxide

The antiarrhythmic efficacy of the novel ultrarapid delayed rectifier potassium current (IKur) blocker (2-isopropyl-5-methylcyclohexyl) diphenylphosphine oxide (DPO-1) was compared with efficacies of the standard class III rapidly activating component of delayed rectifier potassium current (IKr) blockers [+-N-[1'-(6-cyano-1,2,3,4-tetrahydro-2-napthalenyl)-3,4-dihydro-4-hydroxyspiro[2H-1-benzopyran-2,4'-piperidin]-6-yl] methanesulfonamide hydrochloride (MK499) and ibutilide and the class IC agent propafenone in a canine model of Y-shaped intracaval and right atrial free wall surgical lesions producing the substrate for reentrant atrial flutter. Electrocardiographic and cardiac electrophysiologic effects also were assessed at the effective antiarrhythmic doses of test agents. DPO-1 terminated atrial arrhythmia (six/six preparations; 5.5 +/- 2.0 mg/kg i.v.) while significantly increasing atrial relative and effective refractory periods (+15.7 and +15.2%, respectively) but having no significant effects on ventricular refractory periods or electrocardiogram (ECG) intervals. Effective antiarrhythmic doses of MK499 (five/five preparations; 0.004 +/- 0.002 mg/kg i.v.) and ibutilide (five/five preparations; 0.003 +/- 0.001 mg/kg i.v.) similarly increased atrial relative (+23.2 and +25.1%, respectively) and effective (+21.6 and +31.9%, respectively) refractory periods. However, antiarrhythmic doses of MK499 and ibutilide also consistently and significantly increased ventricular relative (+9.9 and +7.6%, respectively) and effective (+10.4 and +9.9%, respectively) refractory periods, rate-corrected ECG QTc (+6.7 and +7.8%, respectively), and paced QT (+7.3 and +8.5%, respectively) intervals. Doses of propafenone that terminated atrial arrhythmia (five/five preparations; 0.94 +/- 0.54 mg/kg i.v.) significantly increased ECG QRS interval (+11.1%). These findings support the approach of atrial selective modulation of refractoriness through block of IKur for the development of potentially safer and more effective atrial antiarrhythmic agents.

[Fate of matrix-bound phosphine during acidification with anaerobic bacteria]

Matrix-bound phosphine of anaerobic granular sludge was studied during methanogenic and acidogenic stage of anaerobic reactors. Results showed that at methanogenic stage, the concentration of matrix-bound phosphine of anaerobic sludge decreased as the height of reactor increased. But during acidogenic stage, matrix-bound phosphine disappeared when pH of the solution declined to 4-5. Further anaerobic static experiments showed that increased acidification and lower pH value promoted the decrease of matrix-bound phosphine. After cultivation with 2 000 mg x L(-1) glucose synthetic wastewater for two days, the matrix-bound phosphine fell from 1.76 ng x kg(-1) to 0.09 ng x kg(-1); At the same time, the highest disappearing rate of phosphine was reached 0.84 ng x (kg x d)(-1). While the glucose synthetic wastewater was 400 mg x L(-1), the disappearing rate of phosphine was only 0.27 ng x (kg x d)(-1). With further cultivation under acidogenic stage, the phosphine decreasing rate slowed down.

Effect of pH on phosphine production and the fate of phosphorus during anaerobic process with granular sludge

The effect of pH on phosphine formation during anaerobic cultivation of granular sludge was investigated. The sludge was taken from full-scale anaerobic reactors treating brewery wastewater. Acetate and phosphate were used as the carbon source and phosphorus source respectively. After 10 days cultivation in the dark, results showed that acidic conditions were more favorable for free phosphine production. At pH 5, the optimum concentration 86.42 ng PH3 m-3 of free phosphine was obtained. The level at pH 7 was reduced to 18.53 ng PH3 m-3, about 1/5 of the maximum. The maximum concentration of matrix-bound phosphine of 3.30 ng PH3 kg-1 wet sludge was achieved at pH 6. More than 83% of the total phosphine was matrix-bound phosphine, which accounted for 0.003-0.009 per thousand of the phosphate removal, while free phosphine comprised 0.00002-0.001 per thousand of the phosphate removal. Most of the phosphorus removal from solution was turned into chemical precipitation or was adsorbed by sludge. The mechanism of the phosphate reduction-step in the formation of phosphine production is still unknown. The promotion of phosphine formation by low pH is compatible with an acidic bio-corrosion mechanism of metal particles in the sludge or of metal phosphides which form phosphine at low pH.

Anion-assisted trans–cis isomerization of palladium(ii) phosphine complexes containing acetanilide functionalities through hydrogen bonding interactions

The anion-assisted shift of trans-cis isomerization equilibrium of a palladium(II) complex containing acetanilide functionalities brought about by allosteric hydrogen bonding interactions has been established by UV/Vis, 1H NMR, 31P NMR and ESI-MS studies.

Effect of intramolecular π–π and CH–π interactions between ligands on structure, electrochemical and spectroscopic properties of fac-[Re(bpy)(CO)3(PR3)]+(bpy = 2,2′-bipyridine; PR3= trialkyl or triarylphosphines)

Intramolecular pi-pi and CH-pi interactions between the bpy and PR3 ligands of fac-[Re(bpy)(CO)3(PR3)]+ affect their structure, and electrochemical and spectroscopic properties. Intramolecular CH-pi interaction was observed between the alkyl groups on the phosphine ligand (R =nBu, Et) and the bpy ligand, and intramolecular pi-pi and CH-pi interactions were both observed between the aryl group(s) on the phosphorus ligand (R =p-MeOPh, p-MePh, Ph, p-FPh, OPh) and the bpy ligand, while no such interactions were found in the trialkylphosphite complexes (R = OiPr, OEt, OMe). The intramolecular interactions distort the pyridine rings of the bpy ligand as long as 3.7 x 10(-2)A in crystals. Molecular orbital calculations of the bpy ligand suggest that this distortion decreases the energy gap between its pi and pi* orbitals. An absorption band attributed to the pi-pi*(bpy) transition of the distorted rhenium complexes, measured in a KBr pellet, was red-shifted by 1-5 nm compared to the complexes without the distorted bpy ligand. Even in solution, similar red shifts of the pi-pi*(bpy) absorption were observed. The redox potential E1/2(bpy/bpy*-) of the complexes with the trialkylphosphine and triarylphosphine ligand are shifted positively by 110-120 mV and 60-80 mV respectively, compared with those derived from the electron-attracting property of the phosphorus ligand. In contrast with these properties, three nu(CO) IR bands, which are sensitive to the electron density on the central rhenium because of pi-back bonding, were shifted to higher energy, and a Re(I/II)-based oxidation wave was observed at a more positive potential according to the electron-attracting property of the phosphorus ligand.

Occurrence and origin of phosphine in landfill gas

A landfill (Hooge Maey, Flanders, Belgium) was subjected to an in-depth study in order to explain the origin of phosphine detected in high amounts in landfill gas, in comparison with biogas from other sources, during a previous study. The spatial and temporal variability of the phosphine concentration in landfill gas was assessed. Twenty-four wells were monitored and differences in phosphine concentration up to one log unit were observed (3.2-32.4 microg/m(3)). The phosphine concentration in each well was constant in time over a period of 4 months. No correlation was found between the phosphine concentration and methane, carbon dioxide, hydrogen sulfide, ethene or ethane concentration. In a series of laboratory tests, it was shown that phosphine was emitted during batch fermentation tests inoculated with landfill leachate when Fe(0) or Al(0) specimens were added. Conditions favouring corrosion of iron gave rise to higher emissions of phosphine. The phosphine concentration in the headspace of a batch test rose to 1.43 mg/m(3) after 27 days of incubation. Weight loss of corroding steel coupons correlated with phosphine emission. Calculations showed that all phosphine emitted from the 0.005 km(3) landfill (160 g/year) could be attributed to corrosion of metals. No evidence of de novo synthesis could be established.

Predicting mortality of phosphine-resistant adults of Sitophilus oryzae (L) (Coleoptera: Curculionidae) in relation to changing phosphine concentration

Adults of a phosphine-resistant strain of Sitophilus oryzae (L) were exposed to constant phosphine concentrations of 0.0035-0.9mg litre(-1) for periods of between 20 and 168h at 25 degrees C, and the effects of time and concentration on mortality were quantified. Adults were also exposed to a series of treatments lasting 48, 72 or 168 h at 25 degrees C, during which the concentration of phosphine was varied. The aim of this study was to determine whether equations from experiments using constant concentrations could be used to predict the efficacy of changing phosphine concentrations against adults of S oryzae. A probit plane without interaction, in which the logarithms of time (t) and concentration (C) were variables, described the effects of concentration and time on mortality in experiments with constant concentrations. A derived equation of the form C(n)t = k gave excellent predictions of toxicity when applied to data from changing concentration experiments. The results suggest that for resistant S oryzae adults there is nothing inherently different between constant and changing concentration regimes, and that data collected from fixed concentrations can be used to develop equations for predicting mortality in fumigations in which phosphine concentration changes. This approach could simplify the prediction of efficacy of typical fumigations in which concentrations tend to rise and then fall over a period of days.

Endogenous Reductants Support the Catalytic Function of Recombinant Rat Cyt19, an Arsenic Methyltransferase

The postulated scheme for the metabolism of inorganic As involves alternating steps of oxidative methylation and of reduction of As from the pentavalent to the trivalent oxidation state, producing methylated compounds containing AsIII that are highly reactive and toxic. S-Adenosyl-L-methionine:AsIII methyltransferase purified from rat liver catalyzes production of methyl and dimethyl arsenicals from inorganic As. This protein is encoded by the cyt19 gene orthologous with cyt19 genes in mouse and human. The reductants dithiothreitol or tris(2-carboxylethyl)phosphine support catalysis by recombinant rat cyt19 (rrcyt19). Coupled systems containing an endogenous reductant (thioredoxin/thioredoxin reductase/NADPH, glutaredoxin/glutathione/glutathione reductase/NADPH, or lipoic acid/thioredoxin reductase/NADPH) support inorganic As methylation by rrcyt19. Although glutathione alone does not support rrcyt19's catalytic function, its addition to reaction mixtures containing other reductants increases the rate of As methylation. Aurothioglucose, an inhibitor of thioredoxin reductase, reduces the rate of As methylation by rrcyt19 in thioredoxin-supported reactions. Addition of guinea pig liver cytosol, a poor source of endogenous As methyltransferase activity, to reaction mixtures containing rrcyt19 shows that endogenous reductants in cytosol support the enzyme's activity. Methylated compounds containing either AsIII or AsV are detected in reaction mixtures containing rrcyt19, suggesting that cycling of As between oxidation states is a component of the pathway producing methylated arsenicals. This enzyme may use endogenous reductants to reduce pentavalent arsenicals to trivalency as a prerequisite for utilization as substrates for methylation reactions. Thus, cyt19 appears to possess both AsIII methyltransferase and AsV reductase activities.

Quantitative determination of loadings and oxidation products of polystyrene-bound phosphines using 31p MAS NMR

The use of (31)P magic angle spinning (MAS) NMR for the quantitative determination of resin loadings and the building up of oxidation products was investigated. Loadings of polystyrene-bound phosphines were evaluated via addition of triphenyl phosphate as reference compound. Results for a series of phosphines are consistent with those obtained from well-established analytical methods. The compounds were also investigated with (13)C MAS NMR, and the individual oxidation stabilities were monitored under oxygen atmosphere.

Anaerobic utilization of phosphite/phosphine as a sole source of phosphorus: implication to growth in the Jovian environment

The objective of the investigation was to isolate anaerobic micro-organisms which had the ability to utilize inorganic phosphorus in forms other than phosphate. The first part of this investigation was to isolate from Cape Canaveral soil micro-organisms capable of utilizing phosphite as their phosphorus source under anaerobic conditions. In an attempt to demonstrate this ability, a medium was prepared which contained hypophosphite as the phosphorus source. This was inoculated with soil samples, and growth was subcultured at least four times. To verify that these isolates could use hypophosphite, they were inoculated into defined hypophosphite medium, and samples were removed periodically and killed with formalin. Growth was determined by turbidity measurements and the sample was then filtered. The filtrate was separated by chromatography and the total amounts of hypophosphite, phosphate and phosphate in the filtrate were measured. By this procedure it appeared that the hypophosphite level began decreasing after 14 hr of incubation suggesting utilization of the hypophosphite under anaerobic conditions. The third part of this investigation used labeled (32P) hypophosphite in a defined medium; the cells were then lysed and the metabolic compounds separated by the use of paper chromatography and autoradiograms, demonstrating the presence of 32P in intermediate metabolic compounds. Similar investigations are now being performed with phosphine as the phosphorus source.

Phosphine and methane generation by the addition of organic compounds containing carbon-phosphorus bonds into incubated soil

Formation of phosphine and methane in anaerobic incubation systems was investigated under stirred and unstirred conditions. The PH3 and CH4 levels in the headspace, as well as the matrix-bound PH3 content in the stirred soil, significantly increased upon the addition of phosphonoacetic acid (P(O)(OH)2CH2COOH). Both the levels of matrix-bound PH3 and CH4 are positively correlated to the buffered dithionite fraction of reactive phosphorus in the soil samples, while a negative correlation was observed between matrix-bound PH3/CH4 levels and the reactive phosphorus fraction.

Proteomic study of a model causative agent of harmful red tide, Prorocentrum triestinum I: Optimization of sample preparation methodologies for analyzing with two-dimensional electrophoresis

A comprehensive study to find the optimal sample preparation conditions for two-dimensional electrophoresis (2-DE) analysis of Prorocentrum triestinum, a model causative agent of harmful algal blooms (HABs) was carried out. The four major sample preparation steps for 2-DE: (a) cell disruption: i.e. sonication and homogenization with glass beads; (b) protein extraction : i.e. sequential and independent extraction procedures; (c) pre-electrophoretic treatment: these included (i) treatment with RNAase/DNAase or benzonase; (ii) ultracentrifugation to sediment large macromolecules such as DNA; (iii) desalting and concentration by ultrafiltration through a Microcon centrifugal filter device (MWCO: 3000 daltons); and (iv) desalting by a micro BioSpin chromatography column (MWCO: 6000 daltons); and (d) rehydration buffers, reducing agents and sample application in the first dimension isoelectric focussing were studied. Our results showed that sonication is easy to perform and resulted in a higher protein yield. Among the four extraction buffers, the urea containing buffers resulted in the extraction of the highest amount of protein while tris(hydroxymethyl)aminomethane buffers and trichloroacetic acid (TCA)/acetone precipitation allowed detection of a higher number of protein species (i.e. protein spots). Desalting by BioSpin and ultrafiltration have improved the 2-DE resolution of the water soluble fraction but have less effect on urea containing fractions. TCA/acetone precipitation was able to desalt all protein fractions independent of the extraction media, however extended exposure to this low pH medium has caused protein modification. Introduction of either DNase/RNase or benzonase treatment did not improve the discriminatory power of the 2-DE but this treatment did yield 2-DE with the clearest background. Proteolytic digestion was inhibited by addition of a protease inhibitor cocktail. Taken overall, a combination of sequential extraction and desalting by BioSpin chromatography for sample treatment before first dimension of 2-DE gave best results based on its simplicity and minimal protein loss. Finally, triscarboxyethylphosphine (TCEP) has performed well as a reducing agent in both the rehydration and equilibration buffers. The rehydration buffer found to be best in this study was 8.0 M urea, 2% 3-[(3-cholamidoprphyldimethylamino]-1-propanesulfonate, 4 mM TCEP and 1% immobilized pH gradient buffer. Subsequently, we applied this finding and performed 2-DE analysis on the soluble protein fractions extracted from light-starved cultured algal cells (nonblooming) and cultured cells grown under optimal conditions (blooming). 2-DE maps of these algal cultures were visibly different and many differentially expressed proteins were found.

Functional properties of the copper-transporting ATPase ATP7B (the Wilson's disease protein) expressed in insect cells

Copper-transporting ATPase ATP7B is essential for normal distribution of copper in human cells. Mutations in the ATP7B gene lead to copper accumulation in a number of tissues and to a severe multisystem disorder, known as Wilson's disease. Primary sequence analysis suggests that the copper-transporting ATPase ATP7B or the Wilson's disease protein (WNDP) belongs to the large family of cation-transporting P-type ATPases, however, the detailed characterization of its enzymatic properties has been lacking. Here, we developed a baculovirus-mediated expression system for WNDP, which permits direct and quantitative analysis of catalytic properties of this protein. Using this system, we provide experimental evidence that WNDP has functional properties characteristic of a P-type ATPase. It forms a phosphorylated intermediate, which is sensitive to hydroxylamine, basic pH, and treatments with ATP or ADP. ATP stimulates phosphorylation with an apparent K(m) of 0.95 +/- 0.25 microm; ADP promotes dephosphorylation with an apparent K(m) of 3.2 +/- 0.7 microm. Replacement of Asp(1027) with Ala in a conserved sequence motif DKTG abolishes phosphorylation in agreement with the proposed role of this residue as an acceptor of phosphate during the catalytic cycle. Catalytic phosphorylation of WNDP is inhibited by the copper chelator bathocuproine; copper reactivates the bathocuproine-treated WNDP in a specific and cooperative fashion confirming that copper is required for formation of the acylphosphate intermediate. These studies establish the key catalytic properties of the ATP7B copper-transporting ATPase and provide a foundation for quantitative analysis of its function in normal and diseased cells.

Modeling of Enterococcus faecalis D-alanine:D-alanine ligase: structure-based study of the active site in the wild-type enzyme and in glycopeptide-dependent mutants

A model for the 3-D structure of Enterococcus faecalis D-Ala:D-Ala ligase was produced using the X-ray structure of the Escherichia coli enzyme complexed with ADP and the methylphosphinophosphate inhibitor as a template. The model passed critical validation criteria with an accuracy similar to that of the template crystallographic structure and showed that ADP and methylphosphinophosphate were positioned in a large empty pocket at the interface between the central and the C-terminal domains, as in E. coli. It evidenced the residues important for substrate binding and catalytic activity in the active site and demonstrated a large body of conserved interactions between the active sites of the E. faecalis and the E. coli D-Ala:D-Ala ligase, the major differences residing in the balance between the hydrophobic and aromatic environment of the adenine. The model also successfully explained the inactivity of four spontaneous mutants (D295 --> V, which impairs interactions with Mg2+ and R293, which are both essential for binding and catalytic activity; S319 --> I, which perturbs recognition of D-Ala2; DAK251-253 --> E, in which the backbone conformation in the vicinity of the deletion remains unaltered but phosphate transfer from ATP is perturbed because of lack of K253; T316 --> I, which causes the loss of a hydrogen bond affecting the positioning of S319 and therefore the binding of D-Ala2). Since D-Ala:D-Ala ligase is an essential enzyme for bacteria, this approach, combining molecular modeling and molecular biology, may help in the design of specific ligands which could inhibit the enzyme and serve as novel antibiotics.

Interaction between the lipoamide-containing H-protein and the lipoamide dehydrogenase (L-protein) of the glycine decarboxylase multienzyme system. 1. Biochemical studies

Lipoamide dehydrogenase or dihydrolipoamide dehydrogenase (EC 1.8.1. 4) is the E3-protein component of the mitochondrial 2-oxoacid dehydrogenase multienzyme complexes. It is also the L-protein component of the glycine decarboxylase system. Although the enzymology of this enzyme has been studied exhaustively using free lipoamide as substrate, no data are available concerning the kinetic parameters of this enzyme with its physiological substrates, the dihydrolipoyl domain of the E2 component (dihydrolipoyl acyltransferase) of the 2-oxoacid dehydrogenase multienzyme complexes or the dihydrolipoyl H-protein of the mitochondrial glycine decarboxylase. In this paper, we demonstrate that Tris(2-carboxyethyl)phosphine, a specific disulfide reducing agent, allows a continuous reduction of the lipoyl group associated with the H-protein during the course of the reaction catalysed by the L-protein. This provided a valuable new tool with which to study the catalytic properties of the lipoamide dehydrogenase. The L-protein displayed a much higher affinity for the dihydrolipoyl H-protein than for free dihydrolipoamide. The oxidation of the dihydrolipoyl H-protein was not affected by the presence of structurally related analogues (apoH-protein or octanoylated H-protein). In marked contrast, these analogues strongly and competitively inhibited the decarboxylation of the glycine molecule catalysed by the P-protein component of the glycine decarboxylase system. Small unfolded proteolytic fragments of the H-protein, containing the lipoamide moiety, displayed Km values for the L-protein close to that found for the H-protein. On the other hand, these fragments were not able to promote the decarboxylation of the glycine in the presence of the P-protein. New highly hydrophilic lipoate analogues were synthesized. All of them showed Km and kcat/Km values very close to that found for the H-protein. From our results we concluded that no structural interaction is required for the L-protein to catalyse the oxidation of the dihydrolipoyl H-protein. We discuss the possibility that one function of the H-protein is to maintain a high concentration of the hydrophobic lipoate molecules in a nonmicellar state which would be accessible to the catalytic site of the lipoamide dehydrogenase.

Phosphine generation by mixed- and monoseptic-cultures of anaerobic bacteria

A microbial basis for bioreductive generation of phosphine is proposed, which could account at least in part for the presence of this toxic gas in natural anaerobic environments and in sewage and landfill gases. Phosphine generation under anaerobic growth conditions was dependent upon both the culture inoculum source (animal faeces) and enrichment culture conditions. Phosphine was detected in headspace gases from mixed cultures under conditions promoting fermentative growth of mixed acid and butyric acid bacteria, either in the presence or absence of methane generation. Monoseptic cultures of certain mixed acid fermentors (Escherichia coli, Salmonella gallinarum, and Salmonella arizonae) and solvent fermentors (Clostridium sporogenes, Clostridium acetobutyricum and Clostridium cochliarium) also generated phosphine. Such fermentative bacteria participate in the multi-stage process of methanogenesis in nature. Generation of phosphine by these bacteria, rather than by methanoarchaea themselves, could explain the apparent correlation between methanogenesis and the formation of phosphine in nature.

Cell surface engineering by a modified Staudinger reaction

Selective chemical reactions enacted within a cellular environment can be powerful tools for elucidating biological processes or engineering novel interactions. A chemical transformation that permits the selective formation of covalent adducts among richly functionalized biopolymers within a cellular context is presented. A ligation modeled after the Staudinger reaction forms an amide bond by coupling of an azide and a specifically engineered triarylphosphine. Both reactive partners are abiotic and chemically orthogonal to native cellular components. Azides installed within cell surface glycoconjugates by metabolism of a synthetic azidosugar were reacted with a biotinylated triarylphosphine to produce stable cell-surface adducts. The tremendous selectivity of the transformation should permit its execution within a cell's interior, offering new possibilities for probing intracellular interactions.

Palladium-catalyzed heteroannulation of 1,3-dienes to form alpha-alkylidene-gamma-butyrolactones

alpha-Alkylidene-gamma-butyrolactones are readily prepared by the palladium-catalyzed heteroannulation of a variety of 1,3-dienes by alpha-iodo and alpha-bromo acrylic acids. The best results are obtained by employing a catalytic amount of the sterically hindered chelating alkyl phosphine D-t-BPF [(di-tert-butylphosphino)ferrocene]. In most cases, this process is highly regioselective. The reaction is believed to proceed via (1) oxidative addition of the vinylic halide to Pd(0), (2) organopalladium addition to the less hindered end of the 1,3-diene to form a pi-allylpalladium intermediate, and (3) nucleophilic displacement of the palladium by the carboxylate ion.

Reducing phosphine after the smoking process using an oxidative treatment

This article gives a description of the setup in a laboratory of a pilot system to reduce phosphine following the smoking process of foodstuffs. At present, this fumigant is released into the atmosphere and causes serious damage to the environment due to its transformation into aggressive compounds. However, phosphine may prove a good alternative to methyl bromide, which will legally be used as a fumigant until the year 2002, provided it is made inert after the smoking process and transformed into nontoxic and easily disposable substances. Oxidant solutions containing potassium permanganate or potassium bichromate in suitable concentrations proved moderately effective in reducing phosphine. The addition of traces of silver nitrate as a catalyst to the oxidant solutions increased the efficiency in reducing the fumigant, although not completely. Thus it was necessary to use a recycling system to decontaminate air from phosphine, as such an apparatus ensures the complete reduction of phosphine. The mathematical function describing how the concentration of phosphine varies in the smoking chamber also makes it possible to estimate the time necessary to reduce a phosphine concentration from any initial value to a fixed final value.

The reductive modulation of chloroplast fructose-1,6-bisphosphatase by tributylphosphine and sodium borohydride

The cleavage of disulfide bonds is the major modification of chloroplast fructose-1,6-bisphosphatase when the light-mediated ferredoxin-thioredoxin system enhances the activity of the enzyme. In vitro, only thiol-bearing compounds are functional in the stimulation of fructose 1,6-bisphosphate hydrolysis. This investigation was undertaken to determine the effectivity of other reductants for enhancing the catalytic capacity. In the presence of 1 mM fructose 1,6-bisphosphate and 0.1 mM Ca2+, the five-fold activation triggered by 3.5 mM tributylphosphine is further potentiated by 15% (v/v) 2-propanol. When the enzyme is incubated in the presence of 0.15 M sodium trichloroacetate in place of the cosolvent, NaH4B initially stimulates the activity but subsequently causes the inactivation of the enzyme. A model developed to analyze this dual effect suggests that the concerted action of fructose 1,6-bisphosphate, Ca2+ and trichloroacetate yields an enzyme form that is slightly activable by reduction (t0.5 = 28 min.). However, chloroplast fructose-1,6-bisphosphatase becomes highly sensitive to trichloroacetate inactivation (t0.5 = 5 min.) when NaH4B reduces fructose 1,6-bisphosphate. Hence, the thiol/disulfide exchange constitutes a particular case of reductive mechanisms that stimulate the activity of chloroplast fructose-1,6-bisphosphatase.

Solubilization of hydrophobic peptides by reversible cysteine PEGylation

"PEG-a-Cys" reagent, synthesized by the esterification of monomethoxy-poly(ethylene glycol) (avg. MW = 5 kDa) to Ellman's reagent [5,5'-dithiobis(2-nitrobenzoic acid)], is shown to "PEGylate" reversibly the cysteine residue of a 25-residue synthetic hydrophobic peptide (H2N-REAAALAAAAALAAWAALCPARRRR-CO2H) designed to model a transmembrane segment of a membrane protein. A mixed disulfide bond was formed between the reagent and the peptide that was readily cleaved with the mild reducing agent tricarboxyethylphosphine hydrochloride (TCEP.HCl). Carboxypeptidase B digestion of the charged carboxyl terminus of the peptide through to the Ala residue--which mimics the enzymatic cleavage of a TM segment from a fusion protein--releases a highly hydrophobic peptide. A time-dependent decrease in the amplitude of the digested peptide circular dichroism (CD) spectra was attributed to the aggregation and/or precipitation of the peptide. While PEGylation of the peptide with PEG-a-Cys had a negligible effect on conformation, it inhibited the loss of CD amplitude in both intact and digested peptides, suggesting that it was effective in solubilization of hydrophobic peptides.

Phosphinic peptides, the first potent inhibitors of astacin, behave as extremely slow-binding inhibitors

A series of phosphinic pseudo-peptides varying in length and composition have been designed as inhibitors of the crayfish zinc endopeptidase astacin, the prototype of the astacin family and of the metzincin superfamily of metalloproteinases. The most efficient phosphinic peptide, fluorenylmethyloxycarbonyl-Pro-Lys-PhePsi(PO2CH2)Ala-P ro-Leu-Val, binds to astacin with a Ki value of 42 nM, which is about three orders of magnitude below the corresponding values for previously used hydroxamic acid derivatives. However, the rate constants for association (kon = 96.8 M-1.s-1) and dissociation (koff = 4.1 x 10(-6) s-1) are evidence for the extremely slow binding behaviour of this compound. N-terminally or C-terminally truncated phosphinic analogues of this parent molecule are much less potent, indicating a critical role of the peptide size on the potency. In particular, omission of the N-terminal proline residue leads to a 40-fold increase in Ki which is mostly due to a 75-fold higher koff value. These findings are consistent with the previously solved crystal structure of astacin complexed with one of the phosphinic peptides, benzyloxycarbonyl-Pro-Lys-PhePsi(PO2CH2)Ala-Pro-O-methyl, Ki = 14 microM [Grams, Dive, Yiotakis, Yiallouros, Vassiliou, Zwilling, Bode and Stöcker (1996) Nature Struct. Biol. 3, 671-675]. This structure also reveals that the phosphinic group binds to the active site as a transition-state analogue. The extremely slow binding behaviour of the phosphinic peptides is discussed in the light of the conformational changes involving a unique 'tyrosine switch' in the structure of astacin upon inhibitor binding. The phosphinic peptides may provide a rational basis for the design of drugs directed towards other members of the astacin family which, like bone morphogenetic protein 1 (BMP1; i.e. the procollagen C-proteinase), have become targets of pharmacological research.

Balancing phosphine in manure fermentation

The evolution of phosphine gas during the anaerobic batch fermentation of fresh swine manure was detected and correlated to the production of methane and hydrogen sulphide. A close temporal relationship between phosphine liberation and methane formation was found. However, the gaseous phosphine released from manure during fermentation only represents a tiny fraction of the overall phosphine balance. The majority of phosphine is captured in solid manure constituents. This matrix-bound phosphine is eliminated by more than 50% during anaerobic batch-fermentation. Seasonally determined phosphine concentrations in biogas and manure from two large-scale manure treatment plants also revealed net losses of phosphine in fermentation. Consequently, manure has to be considered more as a sink of phosphine rather than a phosphine-generating medium. Furthermore, a close relationship between phosphine in the feed of swine and manure of these swine was observed, implying that phosphine residues in the feed (possibly as a result of grain fumigation) represent an important source of phosphine in manure technologies that is relevant before the faecals of swine enter manure treatment plants.

A strategy to locate cysteine residues in proteins by specific chemical cleavage followed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A simple methodology has been developed to characterize the number and location of free cysteine and cystine groups in peptides and proteins, using chemical modification and matrix-assisted laser desorption/ ionization time-of flight mass spectrometry (MALDITOF MS). This new approach employs a specific reaction between free sulfhydryls and 2-nitro-5-thiocyanobenzoic acid (NTCB) to selectively cyanylate cysteine thiols. The N-terminal peptide bond of the modified cysteinyl residue can then be cleaved under alkaline conditions to form an amino-terminal peptide and a series of 2-iminothiazolidine-4-carboxylyl peptides which can be mapped to the sequence by MALDI-MS. The number and location of cysteines can be deduced from mass analysis of the peptide mixture resulting from NTCB chemical processing of the original protein of known sequence under nonreducing conditions. Similar experiments are then performed following disulfide bond reduction to further characterize both cysteine and cystine groups. Experimental conditions are described for protein disulfide bond reduction, sulfhydryl cyanylation, and cleavage reactions performed both in solution and on Zetabind membranes.

Regressors of whole-carcass zinc phosphide/phosphine residues in voles: indirect evidence of low hazards to predators/scavengers

Whole-carcass residues of the rodenticide zinc phosphide (Zn3P2) and hydrolyzed phosphine (PH3) were determined for voles (Microtus spp.) that died following ingestion of a 2% Zn3P2 steam rolled oat (SRO) groats bait. Procedures involved: a three-day acceptance test to assess vole consumption (n = 27) of control SRO groats and several one-day Zn3P2- (n = 13) or control-bait (n = 4) tests to characterize onset of pharmacotoxic signs and to obtain fatally-dosed carcasses for residue analyses. Carcasses were stored in liquid nitrogen (LN2) to maximize retention of Zn3P2/PH3 residues prior to chemical determinations. Linear regressions were computed between pairs of consumption and residue variables. Main results were the following: (1) mean (+/- SD) consumption of control bait was 2.5 (+/- 0.9), 3.0 (+/- 0.9), and 2.8 (+/- 0.8) g on days 1, 2, and 3, respectively (> or = 10.6 +/- 4.6% of body weight); (2) all test-bait voles (n = 13) died approximately 4-12 h after bait presentation, with lethargy and respiratory distress key signs of toxicosis; (3) whole-carcass Zn3P2 residues averaged 1.73 mg (min-max: 0.31-4.95), and PH3 residues averaged 10.6 micrograms (min-max: 0.5-21.0); and (4) significant linear regressions were found between bait consumption/Zn3P2 intake and body weight (r2 = 0.64, p < or = 0.001), carcass Zn3P2 and bait consumption/Zn3P2 intake (r2 = 0.32, p < or = 0.043), and carcass Zn3P2 and body weight (r2 = 0.60, p < or = 0.002). Certain analytical and hazards issues are discussed.