Rare earth elements (REE) in biology and medicine

This survey reports on topics that were presented at the workshop on “Challenges with Rare Earth Elements. The Periodic Table at work for new Science & Technology” hold at the Academia dei Lincei in November 2019. The herein reported materials refer to presentations dealing with studies and applications of rare earth elements (REE) in several areas of Biology and Medicine. All together they show the tremendous impact REE have in relevant fields of living systems and highlight, on one hand, the still existing knowledge gap for an in-depth understanding of their function in natural systems as well as the very important role they already have in providing innovative scientific and technological solutions in a number of bio-medical areas and in fields related to the assessment of the origin of food and on their manufacturing processes. On the basis of the to-date achievements one expects that new initiatives will bring, in a not too far future, to a dramatic increase of our understanding of the REE involvement in living organisms as well as a ramp-up in the exploitation of the peculiar properties of REE for the design of novel applications in diagnostic procedures and in the set-up of powerful medical devices. This scenario calls the governmental authorities for new responsibilities to guarantee a continuous availability of REE to industry and research labs together with providing support to activities devoted to their recovery/recycling.

Transanal Inspection and Management of Low Colorectal Anastomosis Performed With a New Technique: the TICRANT Study

BACKGROUND

Anastomotic leakage is one of the most serious complications after rectal cancer surgery.

METHOD

A prospective multicenter interventional study to assess a newly described technique of creating the colorectal and coloanal anastomosis. The primary outcome was to access the safety and efficacy of this technique in the reduction of anastomotic leak.

RESULT

Fifty-three patients with rectal cancer who underwent low or ultra-low anterior resection were included in the study. There were 35 males and 18 females, with a median age of 68 years (range = 49-89 years). The median tumor distance from the anal verge was 8 cm (range = 4-12 cm), and the median body mass index was 24 kg/m² (range = 20-35 kg/m²). Thirty patients underwent open, 16 laparoscopic, and 7 robotic surgeries. Multiple firing (2-charges) was required in 30 patients to obtain a complete rectal division. Forty-five patients had colorectal anastomosis, and 8 patients had coloanal anastomosis. The protective ileostomy was created in 40 patients at the time of initial surgery. There was no mortality in the first 30 days postoperatively, and only 10 (19%) patients developed complications. There were 3 anastomotic leakages (6%); 2 of them were subclinical with ileostomy created at initial operation and both were treated conservatively with transanal drainage and intravenous antibiotics. One patient required reoperation and ileostomy. The median length of hospital stay was 10 days (range = 4-20 days).

CONCLUSION

Our technique is a safe and efficient method of creation of colorectal anastomosis. It is also a universal method that can be used in open, laparoscopic, and robotic surgeries.

Heme-based catalytic properties of human serum albumin

Human serum albumin (HSA): (i) controls the plasma oncotic pressure, (ii) modulates fluid distribution between the body compartments, (iii) represents the depot and carrier of endogenous and exogenous compounds, (iv) increases the apparent solubility and lifetime of hydrophobic compounds, (v) affects pharmacokinetics of many drugs, (vi) inactivates toxic compounds, (vii) induces chemical modifications of some ligands, (viii) displays antioxidant properties, and (ix) shows enzymatic properties. Under physiological and pathological conditions, HSA has a pivotal role in heme scavenging transferring the metal-macrocycle from high- and low-density lipoproteins to hemopexin, thus acquiring globin-like reactivity. Here, the heme-based catalytic properties of HSA are reviewed and the structural bases of drug-dependent allosteric regulation are highlighted.

Neuroglobin, a pro-survival player in estrogen receptor α-positive cancer cells

Recently, we reported that human neuroglobin (NGB) is a new player in the signal transduction pathways that lead to 17β-estradiol (E2)-induced neuron survival. Indeed, E2 induces in neuron mitochondria the enhancement of NGB level, which in turn impairs the activation of a pro-apoptotic cascade. Nowadays, the existence of a similar pathway activated by E2 in non-neuronal cells is completely unknown. Here, the role of E2-induced NGB upregulation in tumor cells is reported. E2 induced the upregulation of NGB in a dose- and time-dependent manner in MCF-7, HepG2, SK-N-BE, and HeLa cells transfected with estrogen receptor α (ERα), whereas E2 was unable to modulate the NGB expression in the ERα-devoid HeLa cells. Both transcriptional and extranuclear ERα signals were required for the E2-dependent upregulation of NGB in MCF-7 and HepG2 cell lines. E2 stimulation modified NGB intracellular localization, inducing a significant reduction of NGB in the nucleus with a parallel increase of NGB in the mitochondria in both HepG2 and MCF-7 cells. Remarkably, E2 pretreatment did not counteract the H2O2-induced caspase-3 and poly (ADP-ribose) polymerase 1 (PARP-1) cleavage, as well as Bcl-2 overexpression in MCF-7 and HepG2 cells in which NGB was stably silenced by using shRNA lentiviral particles, highlighting the pivotal role of NGB in E2-induced antiapoptotic pathways in cancer cells. Present results indicate that the E2-induced NGB upregulation in cancer cells could represent a defense mechanism of E2-related cancers rendering them insensitive to oxidative stress. As a whole, these data open new avenues to develop therapeutic strategies against E2-related cancers.

17β-Oestradiol anti-inflammatory effects in primary astrocytes require oestrogen receptor β-mediated neuroglobin up-regulation

Neuroglobin (Ngb), so named after its initial discovery in brain neurones, has received great attention as a result of its neuroprotective effects both in vitro and in vivo. Recently, we demonstrated that, in neurones, Ngb is a 17β-oestradiol (E(2) ) inducible protein that is pivotal for hormone-induced anti-apoptotic effects against H(2) O(2) toxicity. The involvement of Ngb in other brain cell populations, as well as in other neuroprotective effects of E(2) , is completely unknown at present. We demonstrate Ngb immunoreactivity in reactive astrocytes located in the proximity of a penetrating cortical injury in vivo and the involvement of Ngb in the E(2) -mediated anti-inflammatory effect in primary cortical astrocytes. Upon binding to oestrogen receptor (ER)β, E(2) enhances Ngb levels in a dose-dependent manner. Although with a lesser degree than E(2) , the pro-inflammatory stimulation with lipopolysaccharide (LPS) also induces the increase of Ngb protein levels via nuclear factor-(NF)κB signal(s). Moreover, a negative cross-talk between ER subtypes and NFκB signal(s) has been demonstrated. In particular, ERα-activated signals prevent the NFκB-mediated Ngb increase, whereas LPS impairs the ERβ-induced up-regulation of Ngb. Therefore, the co-expression of both ERα and ERβ is pivotal for mediating E(2) -induced Ngb expression in the presence of NFκB-activated signals. Interestingly, Ngb silencing prevents the effect of E(2) on the expression of inflammatory markers (i.e. interleukin 6 and interferon γ-inducible protein 10). Ngb can be regarded as a key mediator of the different protective effects of E(2) in the brain, including protection against oxidative stress and the control of inflammation, both of which are at the root of several neurodegenerative diseases.

A neglected giant subcutaneous leiomyosarcoma of the shoulder: a case report

Superficial leiomyosarcoma is an exceeding uncommon malignant tumor, which can be located either cutaneous or subcutaneous tissues. It may occur anywhere in the body, but there is a predilection for the thighs. The distinction between cutaneous or subcutaneous, increased mass size (> 5 cm) and depth are considered to have worst prognosis in terms of recurrence and metastasis. We report a rare case of an 81-year-old woman, presented with a 20-cm leiomyosarcoma of the shoulder. The patient reported that the mass was completely asymptomatic and its growth was slow. A CT study showed a lesion closely apposed to the head of the humerus and revealed no a clear relationship with the surrounding muscles. There was no regional lymphadenopathy or the evidence of metastatic disease. After tumor resection, a large skin and soft-tissue defect was remained and the repair was performed by myocutaneous rotational free flap of latissimus dorsi. The conclusion of the histological analysis was: subcutaneous leiomyosarcoma pT2--grade 1+ (NCI system). The delayed diagnosis and the surgical treatment and giant size of soft tissue leiomyosarcoma may adversely affect the final result.

Gastrointestinal stromal tumours. Is aggressive surgical treatment reasonable in locally advanced cases?

Gastrointestinal stromal tumours (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract and have only recently been described based on their specific immunohistochemistry and the presence of particular kit-related mutations which potentially make them targets for tyrosine kinase inhibition. Most GISTs are respectable, with survival mainly depending upon mitotic count and completeness of resection. Our own and other studies suggest that, in locally advanced cases, complete surgical resection (R0 resection) and adjuvant molecular therapy with imatinib yield good outcomes in terms of survival and disease-free status at 12 and 18 months. This approach, in the light of such integrated surgical-molecular therapy and of the new pharmaceuticals currently under research, means that we can now offer a real chance of recovery and a longer survival period to patients even with advanced-stage illness or local recurrence.

A novel multicompartimental system based on aminated poly(vinyl alcohol) microspheres/succinoylated pullulan microspheres for oral delivery of anionic drugs

Poly(vinyl alcohol) (PVA) microspheres were prepared by dispersion reticulation with glutaraldehyde and further aminated. These microspheres were firstly loaded with diclofenac (DF) and then entrapped in cellulose acetate butyrate (CAB) microcapsules by an o/w solvent evaporation technique for intestinal delivery of drug. The encapsulated PVA microspheres due to their low swelling degree in intestinal fluids, do not have enough force to produce the disruption of CAB shell, therefore different amounts of succinoylated pullulan microspheres (SP-Ms) (exchange capacity up to 5.2 meq/g) were co-encapsulated. The SP-Ms do not swell in acidic pH, but swell up to 20-times in intestinal fluids causing the rupture of CAB shell and facilitating the escape of loaded PVA microspheres.

Nitric oxide impairs the 17beta-estradiol-induced apoptosis in human colon adenocarcinoma cells

Nitric oxide (NO) and 17beta-estradiol (E2) are both important in gastrointestinal health and disease. NO contributes to gastrointestinal motility as well as to inflammation and carcinogenic processes. By contrast, E2 reduces the incidence of colon adenoma and carcinoma by about 30%. We report the genomic and non-genomic E2-estrogen receptor (ER) beta-induced effects in human colon adenocarcinoma. The effect of NO on ERbeta activities was also assessed. The E2-ERbeta-dependent gene transcription was inhibited by exogenous NO, whereas some non-genomic E2-dependent effects (e.g. p38/MAP kinase), important for the activation of the apoptotic cascade, were unaffected by NO. However, NO impaired the E2-induced pro-apoptotic cascade in human colon adenocarcinoma cells by inhibiting caspase-3. The effects of NO may reflect chemical modification(s) of Cys residues present in the DNA recognition domain of ERbeta as well as in the caspase-3 active site. On the whole, high NO concentrations suppressed the E2 protective effects in the gastrointestinal tract, suggesting that the caspase-dependent apoptotic cascade may become critical under conditions of high redox stress such as occur under specific activation of the immune system by chronic infections or pathogen challenge.

[Nitric oxide and anti-protozoan chemotherapy]

Constitutive nitric oxide (NO) is generated by constitutively expressed types of NO-synthase enzymes (NOS-I and -III), being involved in physiological processes such as nervous transmission and vasodilatation. Inducible NO, synthesized by the NO-synthase isoform NOS-II, is an anti-pathogen and tumoricidal agent. However, inducible NO production requires a tight control because of cytotoxic and immune-modulation activity. NO produced by human and canine macrophages has long been demonstrated to be involved in the intracellular killing of Leishmania. Mechanisms of parasite survival and persistence in the host have been throughly investigated, and include suppression of NOS-II and the parasite entry into NOS-II negative cells. Both intracellular and extracellular morphotypes of Trypanosoma cruzi are killed by NO in vitro and in vivo, although a role of NO in the pathogenesis of heart disease has been reported. Killing of extracellular protozoa such as Trichomonas vaginalis and Naegleria fowleri by activated macrophages is also mediated by NO. The main control of Plasmodium spp infection in human and murine hepatocytes, and in human monocytes is achieved by NO-mediated mechanisms. Protection from severe malaria in African children has been found associated with polymorphisms of the NOS-II promoter; however, a pathogenic role of endogenous NO has been documented in cerebral malaria. Although several macromolecules are putative NO targets, recent experimental work has shown that NO-releasing compounds inhibit cysteine proteases (CP) of P. falciparum, T. cruzi and L. infantum in a dose-dependent manner. CPs are present in a wide range of parasitic protozoa and appear to be relevant in several aspects of the life cycle and of the parasite-host relationships. Comparative analysis of 3-D amino acid sequence models of CPs from a broad range of living organisms, from viruses to mammals, suggests that the Sy atom of the Cys catalytic residue undergoes NO-dependent chemical modification (S-nytrosilation and disulfide bridge formation), with the concomitant loss of enzyme activity. The NO-donor S-nitroso-N-acetilpenicillamine (SNAP) was shown to kill T. cruzi epimastigotes and L. infantum promastigotes in culture, while a combination of nitrite plus acid organic salts was highly effective against L. major amastigotes in mouse macrophages. A parasitostatic effect--with both encystation and excystation inhibition--of S-nitrosoglutathione and spermine-NONOate was documented in trophozoite cultures of Giardia duodenalis. Recently, a novel formulation of metronidazole bearing a NO-releasing group was found to enhance significantly the in vitro killing of Entamoeba histolytica trophozoites, compared to metronidazole. So far, only two clinical studies were performed on human patients, suffering from cutaneous leishmaniasis. In one study, 16 Ecuadorean patients were treated with a SNAP cream administered on lesions for 10 days. All lesions were parasitologically cured and clinically healed by day 30. In the second study, a different NO-producing cream (basically nitrite in acidic environment) was employed to treat 40 Syrian patients. Only 28% of them showed improvement and 12% were cured by day 60. In conclusion, despite the wide evidence that NO can be regarded as a natural anti-protozoal weapon, little efforts have been made to develop and test NO-based drugs in human medicine. This is mainly due to the difficulty in designing suitable chemical carriers able to release the right amount of NO, in the right place and in the right time, to avoid toxic effects against non-target host cells.

Inhibition of Saccharomyces cerevisiae phosphomannose isomerase by the NO-donor S-nitroso-acetyl-penicillamine

Phosphomannose isomerase (PMI; EC. 5.3.1.8) is an essential metalloenzyme in the early steps of the protein glycosylation pathway in both prokaryotes and eukaryotes. The Cys150 residue (according to Candida albicans PMI numbering) is conserved in the active centre of mammalian and yeast PMI, but not in bacterial species where it is replaced by Asn. Here, the dose- and time-dependent inhibitory effect of the NO-donor S-nitroso-acetyl-penicillamine on the Saccharomyces cerevisiae PMI catalytic activity is reported. The analysis of the X-ray crystal structure of C. albicans PMI and of the molecular model of S. cerevisiae PMI provides a rationale for the low reactivity of Cys150 towards alkylating and nitrosylating agents.

Effect of ibuprofen and warfarin on the allosteric properties of haem-human serum albumin. A spectroscopic study

Haem binding to human serum albumin (HSA) endows the protein with peculiar spectroscopic properties. Here, the effect of ibuprofen and warfarin on the spectroscopic properties of ferric haem-human serum albumin (ferric HSA-haem) and of ferrous nitrosylated haem-human serum albumin (ferrous HSA-haem-NO) is reported. Ferric HSA-haem is hexa-coordinated, the haem-iron atom being bonded to His105 and Tyr148. Upon drug binding to the warfarin primary site, the displacement of water molecules--buried in close proximity to the haem binding pocket--induces perturbation of the electronic absorbance properties of the chromophore without affecting the coordination number or the spin state of the haem-iron, and the quenching of the 1H-NMR relaxivity. Values of Kd for ibuprofen and warfarin binding to the warfarin primary site of ferric HSA-haem, corresponding to the ibuprofen secondary cleft, are 5.4 +/- 1.1 x 10(-4) m and 2.1 +/- 0.4 x 10(-5) m, respectively. The affinity of ibuprofen and warfarin for the warfarin primary cleft of ferric HSA-haem is lower than that reported for drug binding to haem-free HSA. Accordingly, the Kd value for haem binding to HSA increases from 1.3 +/- 0.2 x 10(-8) m in the absence of drugs to 1.5 +/- 0.2 x 10(-7) m in the presence of ibuprofen and warfarin. Ferrous HSA-haem-NO is a five-coordinated haem-iron system. Drug binding to the warfarin primary site of ferrous HSA-haem-NO induces the transition towards the six-coordinated haem-iron species, the haem-iron atom being bonded to His105. Remarkably, the ibuprofen primary cleft appears to be functionally and spectroscopically uncoupled from the haem site of HSA. Present results represent a clear-cut evidence for the drug-induced shift of allosteric equilibrium(a) of HSA.

Crystallization and preliminary X-ray analysis of neural haemoglobin from the nemertean worm Cerebratulus lacteus

The nemertean worm Cerebratulus lacteus neural tissue haemoglobin (109 amino acids, the shortest known haemoglobin) has been overexpressed in Escherichia coli, purified and crystallized. A highly redundant native data set has been collected at the Cu K(alpha) wavelength to 2.05 A resolution. The crystals belong to the orthorhombic P2(1)2(1)2(1) space group, with unit-cell parameters a = 42.5, b = 43.1, c = 60.2 A and one molecule per asymmetric unit. The anomalous difference Patterson map clearly reveals the position of the haem Fe atom, thus paving the way for MAD/SAD structure determination.

Contryphan-Vn: a novel peptide from the venom of the Mediterranean snail Conus ventricosus

The isolation, purification, and biochemical characterization of the novel peptide Contryphan-Vn, extracted from the venom of the Mediterranean marine snail Conus ventricosus, is reported. Contryphan-Vn is the first Conus peptide described from a vermivorous species and the first purified from the venom of the single Mediterranean Conus species. The amino acid sequence of Contryphan-Vn is As with other contryphans, Contryphan-Vn contains a d-tryptophan residue, is amidated at the C-terminus, and maintains the five-residue intercystine loop size. However, Contryphan-Vn differs from the known contryphans by the insertion of the Asp residue at position 2, by the lack of hydroxylation of Pro(4), and, remarkably, by the presence of the basic residue Lys(6) within the intercystine loop. Although the biological function(s) of contryphans is still unknown, these characteristics suggest distinct molecular target(s) and/or function(s) for Contryphan-Vn.

Nitric oxide inhibits selectively the 17beta-estradiol-induced gene expression without affecting nongenomic events in HeLa cells

17beta-Estradiol (E2) induces genomic (i.e., pC3-luciferase promoter-reporter construct expression) and nongenomic (i.e., DNA synthesis and IP(3) production) effects in HeLa cells only after transient transfection with the human estrogen receptor alpha (ERalpha) reporter plasmid. Here the effect of nitric oxide (NO) on both E2-induced effects in transiently transfected HeLa cells is reported. Remarkably, the E2-dependent gene transcription is inhibited dose-dependently by NO. By contrast, DNA synthesis and IP(3) production, representing nongenomic E2-dependent effects, are unaffected by NO. The selective NO action on E2-induced functions may be related to NO-mediated chemical modification(s) of the Cys residues present in the DNA recognition domain of ERalpha impairing DNA binding.

Monomer-dimer equilibrium and oxygen binding properties of ferrous Vitreoscilla hemoglobin

The monomer-dimer equilibrium and the oxygen binding properties of ferrous recombinant Vitreoscilla hemoglobin (Vitreoscilla Hb) have been investigated. Sedimentation equilibrium data indicate that the ferrous deoxygenated and carbonylated derivatives display low values of equilibrium dimerization constants, 6 x 10(2) and 1 x 10(2) M(-1), respectively, at pH 7.0 and 10 degrees C. The behavior of the oxygenated species, as measured in sedimentation velocity experiments, is superimposable to that of the carbonylated derivative. The kinetics of O(2) combination, measured by laser photolysis at pH 7.0 and 20 degrees C, is characterized by a second-order rate constant of 2 x 10(8) M(-1) s(-1) whereas the kinetics of O(2) release at pH 7.0 is biphasic between 10 and 40 degrees C, becoming essentially monophasic below 10 degrees C. Values of the first-order rate constants (at 20 degrees C) and of the activation energies for the fast and slow phases of the Vitreoscilla Hb deoxygenation process are 4.2 s(-1) and 19.2 kcal mol(-1) and 0.15 s(-1) and 24.8 kcal mol(-1), respectively. Thus the biphasic kinetics of Vitreoscilla Hb deoxygenation is unrelated to the association state of the protein. The observed biphasic oxygen release may be accounted for by the presence of two different conformers in thermal equilibrium within the monomer. The two conformers may be assigned to a structure in which the heme-iron-bound ligand is stabilized by direct hydrogen bonding to TyrB10 and a structure in which such interaction is absent. The slow interconversion between the two conformers may reflect a very large conformational rearrangement in the disordered distal pocket segment connecting helices C and E.

Does myoglobin protect Trypanosoma cruzi from the antiparasitic effects of nitric oxide?

The hemoflagellate protozoan parasite Trypanosoma cruzi is the causative agent of Chagas disease, a progressive fatal cardiomyopathy widespread in South and Central America. Here, we postulate that the preferential colonization of cardiomyocytes by T. cruzi may reflect the role of myoglobin (Mb) as a nitric oxide (NO) scavenger, protecting the parasite from the trypanocidal effects of NO. The proposal of this novel function of Mb is based on knowledge that ferrous oxygenated Mb reacts rapidly and irreversibly with NO yielding nitrate and ferric oxidized Mb, which is reduced back to the physiologically active form by an intracellular reductase. The postulated protective role of Mb on the viability of T. cruzi is reminiscent of that postulated for hemoglobin in protecting intraerythrocytic Plasmodia from the parasiticidal effect of NO.

Very high resolution structure of a trematode hemoglobin displaying a TyrB10-TyrE7 heme distal residue pair and high oxygen affinity

Monomeric hemoglobin from the trematode Paramphistomum epiclitum displays very high oxygen affinity (P(50)<0.001 mm Hg) and an unusual heme distal site containing tyrosyl residues at the B10 and E7 positions. The crystal structure of aquo-met P. epiclitum hemoglobin, solved at 1.17 A resolution via multiwavelength anomalous dispersion techniques (R-factor=0.121), shows that the heme distal site pocket residue TyrB10 is engaged in hydrogen bonding to the iron-bound ligand. By contrast, residue TyrE7 is unexpectedly locked next to the CD globin region, in a conformation unsuitable for heme-bound ligand stabilisation. Such structural organization of the E7 distal residue differs strikingly from that observed in the nematode Ascaris suum hemoglobin (bearing TyrB10 and GlnE7 residues), which also displays very high oxygen affinity. The oxygenation and carbonylation parameters of wild-type P. epiclitum Hb as well as of single- and double-site mutants, with residue substitutions at positions B10, E7 and E11, have been determined and are discussed here in the light of the protein atomic resolution crystal structure.

Relaxometric characterization of human hemalbumin

Hemalbumin [i.e., Fe(III)-protoporphyrin IX-human serum albumin; Fe(III)heme-HSA] is an important intermediate in the recovery of heme iron following hemolysis. Relaxometric data are consistent with the occurrence of a hexacoordinated high-spin Fe(III) center with no water in the inner coordination sphere. The relatively high relaxation enhancement observed for an aqueous solution of Fe(III)heme-HSA (r1p=4.8 mM(-1)s(-1) at 20 MHz, pH 7, and 25 C) is ascribed to the occurrence of a strong contribution from water molecules in the second coordination sphere. Structural analysis of the putative binding region has been performed by a Monte Carlo simulated annealing procedure, which allowed us to identify His105 and Tyr148 as axial ligands. The role of a tyrosinate as the sixth Fe(III)heme ligand is supported by the pH-dependent analysis. Interestingly, when Fe(III) is replaced by Mn(III), the occurrence of a fast exchanging water molecule at pH values close to neutrality is detected. As the pH is increased, the Mn(III) containing system behaves analogously to Fe(III)heme-HSA. At higher pH, the phenolate ligand is eventually displaced by OH- from both Fe(III) and Mn(III) centers. Support for the proposed bonding scheme has been gained also from competitive binding assays for the sixth coordination site by fluoride, azide, and imidazole ligands.

Modulation of the catalytic activity of cruzipain, the major cysteine proteinase from Trypanosoma cruzi, by temperature and pH

Cysteine proteinases are relevant to several aspects of the parasite life cycle and of parasite-host relationships. Here, a quantitative investigation of the effect of temperature and pH on the total substrate inhibition of cruzipain, the major papain-like cysteine proteinase from Trypanosoma cruzi, is reported. Values of the apparent catalytic and inhibition parameters Km, Vmax, Vmax/Km, and K(i) for the cruzipain-catalysed hydrolysis of N-alpha-benzyloxycarbonyl-L-phenylalanyl-L-arginine-(7-amino-4-methylcoumarin) (Z-Phe-Arg-AMC) and azocasein were determined between 10.0 degrees C and 40.0 degrees C and between pH 4.5 and 8.5. Values of Km were independent of temperature and pH, whereas values of Vmax, Vmax/Km, and K(i) were temperature-dependent and pH-dependent. Over the whole pH range explored, values of logVmax, log(Vmax/Km), and logK(i) increased linearly with respect to T(-1). Values of Vmax and Vmax/Km were affected by the acid-base equilibrium of one temperature-independent ionizing group (i.e. pK(unl)' = pK(lig)' = 5.7 +/- 0.1, at 25.0 degrees C). Moreover, values of K(i) were affected by the alkaline pK shift of one ionizing group of active cruzipain (from pK(unl)" = 5.7 +/- 0.1 to pK(lig)" = 6.1 +/- 0.1, at 25.0 degrees C) upon Z-Phe-Arg-AMC binding. Values of logK(unl)', logK(lig)', and logK(lig)" were temperature-independent. Conversely, values of logK(unl)" were linearly dependent on T(-1). As a whole, total substrate inhibition of cruzipain decreased with increasing temperature and pH. These data suggest that both synthetic and protein substrates can bind to the unique active centre of cruzipain either productively or following a binding mode which results in enzyme inhibition. However, allosteric effect(s) cannot be excluded.

Inhibition of cysteine protease activity by NO-donors

Cysteine proteases represent a broad class of proteolytic enzymes widely distributed among living organisms. Although well known as typical lysosomal enzymes, cysteine proteases are actually recognized as multi-function enzymes, being involved in antigen processing and presentation, in membrane-bound protein cleavage, as well as in degradation of the cellular matrix and in processes of tissue remodeling. Very recently, it has been shown that the NO(-donor)-mediated chemical modification of the Cys catalytic residue of cysteine proteases, including Coxsackievirus and Rhinovirus cysteine proteases, cruzain, Leishmania infantum cysteine protease, falcipain, papain, as well as mammalian caspases, cathepsins and calpain, blocks the enzyme activity in vitro and in vivo. Here, inhibition of representative cysteine proteases by NO(-donors) is reviewed.

Effect of bezafibrate and clofibrate on the heme–iron geometry of ferrous nitrosylated heme–human serum albumin: an EPR study

The effect of bezafibrate (BZF) and clofibrate (CF), two therapeutic drugs displaying anticoagulant and antihyperlipoproteinemic activities, on the EPR-spectroscopic properties of ferrous nitrosylated heme-human serum albumin (HSA-heme-NO) has been investigated. In the absence of BZF and CF, HSA-heme-NO is a five-coordinate heme-iron system, characterised by an X-band EPR spectrum with a three-line splitting in the high magnetic field region. Addition of BZF and CF to HSA-heme-NO induced the transition towards a six-coordinate heme-iron species characterised by an X-band EPR spectrum with an axial geometry. These data indicate that HSA-heme-NO is a five-coordinate heme-iron system, BZF and CF acting as allosteric effectors, and show that the primary heme binding site and the CF cleft of HSA are conformationally-linked, regardless of their different location.

Structural bases for inhibitor binding and catalysis in polyamine oxidase

Polyamine oxidase (PAO) carries out the FAD-dependent oxidation of the secondary amino groups of spermidine and spermine, a key reaction in the polyamine catabolism. The active site of PAO consists of a 30 A long U-shaped catalytic tunnel, whose innermost part is located in front of the flavin ring. To provide insight into the PAO substrate specificity and amine oxidation mechanism, we have investigated the crystal structure of maize PAO in the reduced state and in complex with three different inhibitors, guazatine, 1,8-diaminooctane, and N(1)-ethyl-N(11)-[(cycloheptyl)methyl]-4,8-diazaundecane (CHENSpm). In the reduced state, the conformation of the isoalloxazine ring and the surrounding residues is identical to that of the oxidized enzyme. Only Lys300 moves away from the flavin to compensate for the change in cofactor protonation occurring upon reduction. The structure of the PAO.inhibitor complexes reveals an exact match between the inhibitors and the PAO catalytic tunnel. Inhibitor binding does not involve any protein conformational change. Such lock-and-key binding occurs also in the complex with CHENSpm, which forms a covalent adduct with the flavin N5 atom. Comparison of the enzyme complexes hints at an "out-of-register" mechanism of inhibition, in which the inhibitor secondary amino groups are not properly aligned with respect to the flavin to allow oxidation. Except for the Glu62-Glu170 pair, no negatively charged residues are involved in the recognition of substrate and inhibitor amino groups, which is in contrast to other polyamine binding proteins. This feature may be exploited in the design of drugs specifically targeting PAO.

NO donors inhibit Leishmania infantum cysteine proteinase activity

Nitric oxide (NO) releasing drugs (e.g., glyceryl trinitrate) were successfully used in the treatment of cutaneous leishmaniasis in man. In the present study, the effect of NO donors on the catalytic activity of the cysteine proteinase from promastigotes of Leishmania infantum, an agent of Old World visceral and cutaneous leishmaniases, is reported. In particular, one equivalent of NO, released by the NO donors S-nitrosoglutathione, glyceryl trinitrate, (+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide, 3-morpholinosydnonimine, S-nitrosoacetylpenicillamine and sodium nitroprusside, inhibited one equivalent of the parasite cysteine proteinase. As expected, NO-deprived compounds did not affect the catalytic activity of the parasite cysteine proteinase. Furthermore, the absorption spectrum of the (+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide-treated inactive L. infantum enzyme displayed a maximum in the 330-350 nm wavelength range. The reducing agents dithiothreitol and L-ascorbic acid completely prevented parasite cysteine proteinase inhibition by NO, fully restored the catalytic activity, and reversed the NO-induced absorption spectrum of the inactive enzyme. Moreover, S-nitrosoacetylpenicillamine displayed a leishmanicidal effect, inhibiting the cysteine proteinase activity in vivo. As expected, the NO-deprived compound N-acetylpenicillamine did not affect significantly the parasite viability and the enzyme activity in vivo. These data suggest that the L. infantum cysteine proteinase undergoes NO-mediated S-nitrosylation, thereby representing a possible mechanism of antiparasitic host defence.

Selective inhibition of human mast cell tryptase by gabexate mesylate, an antiproteinase drug

Gabexate mesylate is a non-antigenic synthetic inhibitor of trypsin-like serine proteinases that is therapeutically used in the treatment of pancreatitis and disseminated intravascular coagulation and as a regional anticoagulant for hemodialysis. Considering the structural similarity between gabexate mesylate and arginine-based inhibitors of trypsin-like serine proteinases, the effect of gabexate mesylate on human and bovine mast cell tryptase action was investigated. Values of the inhibition constant (K(i)) for gabexate mesylate binding to human and bovine tryptase were 3.4 x 10(-9) M and 1.8 x 10(-7) M (at pH 7.4 and 37.0 degrees ), respectively. Furthermore, gabexate mesylate inhibited the fibrinogenolytic activity of human tryptase. On the basis of the available x-ray crystal structure of human tryptase, the possible binding mode of gabexate mesylate to human and bovine tryptase was analyzed. Human tryptase inhibition by gabexate mesylate may account for the reported prevention of inflammation, erosion, and ulceration of skin and mucosae.

Inhibition of pig liver and Zea mays L. polyamine oxidase: a comparative study

Polyamine oxidase (PAO) is involved in polyamine metabolism and production of hydrogen peroxide in animal and plants, thus representing a key system in development and programmed cell death. In the present study, the inhibitory effect of amiloride, p-aminobenzamidine, clonidine, 4',6-diamidino-2-phenyl-indole (DAPI), gabexate mesylate, guazatine, and N,N'-bis(2,3-butadienyl)-1,4-butane-diamine (MDL72527) on the catalytic activity of pig liver and Zea mays L. PAO, Lens culinaris L. and Pisum sativum L. and swine kidney copper amine oxidase, bovine trypsin, as well as neuronal constitutive nitric oxide synthase (NOS-I) was investigated. Moreover, agmatine and N(3) -prenylagmatine (G3) were observed to inhibit pig liver and Zea mays L. PAO, bovine trypsin, and NOS-I action, but were substrates for Lens culinaris L., Pisum sativum L. and swine kidney copper amine oxidase. Guazatine and G3 inhibited selectively Zea mays L. PAO with K(i) values of 7.5 x 10(-9) M and 1.5 x 10(-8) M, respectively (at pH 6.5 and 25.0 degrees C). As a whole, the data reported here represent examples of enzyme cross-inhibition, and appear to be relevant in view of the use of cationic L-arginine-and imidazole-based compounds as drugs.

Characterization of five new low-molecular-mass trypsin inhibitors from white mustard (Sinapis alba L.) seed

Five new low-molecular-mass trypsin inhibitors belonging to the RTI/MTI-2 family were identified from white mustard (Sinapis alba L. ; MTI-2) seed. Purified MTI-2 consisted of a peptide mixture, displaying Ile or Arg at position 43, Trp or kynurenine (Kyn) at position 44, and C-terminal ragged ends. The occurrence of Ile or Arg at position 43 suggested that MTI-2 inhibitors originated from different genes. The presence of 5-oxo-proline (pyroglutamic acid; 5-oxoPro1) and Kyn44 reflected post-translational processing of the serine proteinase inhibitor. MTI-2 showed approximately 70% amino-acid identity with low-molecular-mass trypsin inhibitors isolated from oil rape (Brassica napus var. oleifera; RTI-III) seed and with serine proteinase inhibitors mapped in Arabidopsis thaliana chromosome II (ATTI). Furthermore, MTI-2 was homologous to brazzein, the sweet-tasting protein from Pentadiplandra brazzeana Baillon fruit ( approximately 30% amino-acid identity). Although snake-venom toxins showed a low amino-acid identity (< 20%) with MTI-2, RTI-III, and ATTI, some structurally relevant residues were conserved. The disulfide bridge pattern of MTI-2 (Cys5-Cys27, Cys18-Cys31, Cys42-Cys52, and Cys54-Cys57) corresponded to that of RTI-III and of snake-venom toxins, being different from that of brazzein. Therefore, protein similarity might be attributable to the three-dimensional arrangement rather than to the amino-acid sequence. Values of Ka for MTI-2 binding to bovine beta-trypsin (trypsin) and bovine alpha-chymotrypsin were 6.3 x 109 M-1 and 2.0 x 106 M-1, respectively, at pH 8.0 and 21.0 degrees C. Moreover, values of kon for MTI-2 binding to trypsin and of koff for the dissociation of the serine proteinase:inhibitor complex were 5.6 x 105 M-1.s-1 and 8.9 x 10-5 M-1.s-1, respectively, at pH 8.0 and 21.0 degrees C. Despite the heterogeneity of the purified inhibitor peptide mixture, the inhibition properties of the different MTI-2 inhibitors were indistinguishable.

Determination of H(2)S solubility via the reaction with ferric hemoglobin I from the bivalve mollusc Lucina pectinata

A new, simple and fast spectrophotometric method for the determination of the H(2)S concentration is reported. This method, based on the 1:1 reaction between H(2)S and the ferric derivative of hemoglobin I (HbI) from the bivalve mollusc Lucina pectinata, allows the quantitative determination of H(2)S dissolved in a given solution even at concentrations as low as 1 x 10(-6) M. Note that L. pectinata HbI is considered the physiological receptor of H(2)S.

A chimeric mini-trypsin inhibitor derived from the oil rape proteinase inhibitor type III

The design of chimeric proteins is a major field of interest in structural biology and biotechnology. The successful design of the chimeric protein composed by the minimized reactive site domain of the low-molecular-mass trypsin inhibitor from Brassica napus (var. oleifera) seed (Ser3-Lys35; mini-RTI-III) and murine dihydrofolate reductase (DHFR) is reported here. The DHFR-mini-RTI-III chimeric protein was expressed in Escherichia coli, purified by metal-chelate affinity chromatography and oxidatively refolded. The affinity of the purified and refolded DHFR-mini-RTI-III for bovine trypsin (K = 5.0 x 10(-10) M) was closely similar to that determined for native RTI-III (K = 2.9 x 10(-10) M), at pH 8.2 and 22.0 degrees C. DHFR-mini-RTI-III may be regarded as a tool in structure-function studies and for developing multifunctional and multidomain proteinase inhibitors.

Selective inhibition of nitric oxide synthase type I by clonidine, an anti-hypertensive drug

Clonidine, clinically used in the treatment of hypertension, is a central alpha(2)-adrenergic agonist that reduces blood pressure and slows heart rate by reducing sympathetic stimulation. Considering the structural similarity between clonidine and hydrophobic heterocyclic nitric oxide synthase (NOS) inhibitors, the effect of clonidine on the nitric oxide (NO) pathway was investigated. This was verified by determination of NOS activity in vitro and by analysis of inducible Ca(2+)-independent NOS (NOS-II) mRNA expression and measurement of nitrite levels in rat C6 glioma cells, taken as a cellular model. Clonidine inactivated neuronal Ca(2+)-dependent NOS (NOS-I) competitively without affecting NOS-II and endothelial Ca(2+)-dependent NOS (NOS-III) activity. However, the value of K(i) for clonidine binding to NOS-I depended on tetrahydrobiopterin (BH(4)) concentration, as reported for NOS inhibition by other nitrogen heterocyclic compounds. In particular, the value of K(i) for clonidine binding to NOS-I increased (from [7. 9 +/- 0.4] x 10(-5) M to [8.0 +/- 0.4] x 10(-3) M) as BH(4) concentration was increased (between 3.0 x 10(-7) M and 1.0 x 10(-3) M), at pH 7.5 and 37.0 degrees. In addition, clonidine (1.0 x 10(-4) M) enhanced NOS-II mRNA expression in rat C6 glioma cells, as induced by Escherichia coli lipopolysaccharide (LPS) plus interferon-gamma (IFN-gamma). Finally, clonidine (1.0 x 10(-4) M to 1.0 x 10(-3) M) dose dependently increased the levels of LPS/IFN-gamma-induced nitrites, the breakdown product of NO, in supernatants of rat C6 glioma cells. As reported for other NOS inhibitors, clonidine was also able to regulate NOS-I and NOS-II inversely.

Re-evaluation of amino acid sequence and structural consensus rules for cysteine-nitric oxide reactivity

Nitric oxide (NO), produced in different cell types through the conversion of L-arginine into L-citrulline by the enzyme NO synthase, has been proposed to exert its action in several physiological and pathological events. The great propensity for nitrosothiol formation and breakdown represents a mechanism which modulates the action of macromolecules containing NO-reactive Cys residues at their active centre and/or allosteric sites. Based on the human haemoglobin (Hb) structure and accounting for the known acid-base catalysed Cys beta93-nitrosylation and Cys beta393NO-denitrosylation processes, the putative amino acid sequence (Lys/Arg/His/Asp/Glu)Cys(Asp/Glu) (sites -1, 0, and + 1, respectively) has been proposed as the minimum consensus motif for Cys-NO reactivity. Although not found in human Hb, the presence of a polar amino acid residue (Gly/Ser/Thr/Cys/Tyr/Asn/Gln) at the -2 position has been observed in some NO-reactive protein sequences (e.g., NMDA receptors). However, the most important component of the tri- or tetra-peptide consensus motif has been recognised as the Cys(Asp/Glu) pair [Stamler et al., Neuron (1997) 18, 691-696]. Here, we analyse the three-dimensional structure of several proteins containing NO-reactive Cys residues, and show that their nitrosylation and denitrosylation processes may depend on the Cys-Sy atomic structural microenvironment rather than on the tri- or tetra-peptide sequence consensus motif.

A novel two-over-two alpha-helical sandwich fold is characteristic of the truncated hemoglobin family

Small hemoproteins displaying amino acid sequences 20-40 residues shorter than (non-)vertebrate hemoglobins (Hbs) have recently been identified in several pathogenic and non-pathogenic unicellular organisms, and named 'truncated hemoglobins' (trHbs). They have been proposed to be involved not only in oxygen transport but also in other biological functions, such as protection against reactive nitrogen species, photosynthesis or to act as terminal oxidases. Crystal structures of trHbs from the ciliated protozoan Paramecium caudatum and the green unicellular alga Chlamydomonas eugametos show that the tertiary structure of both proteins is based on a 'two-over-two' alpha-helical sandwich, reflecting an unprecedented editing of the classical 'three-over-three' alpha-helical globin fold. Based on specific Gly-Gly motifs the tertiary structure accommodates the deletion of the N-terminal A-helix and replacement of the crucial heme-binding F-helix with an extended polypeptide loop. Additionally, concerted structural modifications allow burying of the heme group and define the distal site, which hosts a TyrB10, GlnE7 residue pair. A set of structural and amino acid sequence consensus rules for stabilizing the fold and the bound heme in the trHbs homology subfamily is deduced.

Nitric oxide inhibits cruzipain, the major papain-like cysteine proteinase from Trypanosoma cruzi

Nitric oxide (NO) is a pluripotent regulatory molecule showing, among others, an antiparasitic activity. Moreover, NO inhibits cysteine proteinase action by nitrosylating the Cys catalytic residue. In the present study, the inhibitory effect of the substrate N-alpha-benzyloxycarbonyl-L-phenylalanyl-L-arginine-(7-amino-4-methyl coumarin) and of NO on the catalytic activity of cruzipain, the major papain-like cysteine proteinase from Trypanosoma cruzi (the hemoflagellate protozoan parasite which causes the American trypanosomiasis), is reported. In particular, NO-donors S-nitroso-glutathione (GSNO), (+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (NOR-3), 3-morpholinosydnonimine (SIN-1), S-nitroso-acetyl-penicillamine (SNAP), and sodium nitroprusside (SNP) dose-dependently inhibited cruzipain, this effect being likely attributable to the S-nitrosylation of the Cys25 catalytic residue. These results were analyzed in parallel with those concerning the inhibitory effect of the substrate and of NO on the catalytic activity of falcipain, the cruzipain-homologous cysteine proteinase from Plasmodium falciparum. The modulation of the cruzipain and falcipain activity by NO may be relevant in developing new strategies against T. cruzi and P. falciparum in human host. As a whole, the NO-mediated S-nitrosylation of pathogenic viral, bacterial, fungal, and parasitic cysteine proteinases may represent a general mechanism of antimicrobial and antiparasitic host defences.

Serine proteinase inhibition by the active site titrant N alpha-(N, N-dimethylcarbamoyl)-alpha-azaornithine p-nitrophenyl ester. A comparative study

Kinetics for the hydrolysis of the chromogenic active-site titrant N alpha-(N,N-dimethylcarbamoyl)-alpha-azaornithine p-nitrophenyl ester (Dmc-azaOrn-ONp) catalysed by bovine beta-trypsin, bovine alpha-thrombin, bovine Factor Xa, human alpha-thrombin, human Factor Xa, human Lys77-plasmin, human urinary kallikrein, Mr 33 000 and Mr 54 000 species of human urokinase, porcine pancreatic beta-kallikrein-A and -B and Ancrod (the coagulating serine proteinase from the Malayan pit viper Agkistrodon rhodostoma venom) have been obtained between pH 6.0 and 8.0, at 21.0 degrees C, and analysed in parallel with those for the enzymatic cleavage of N alpha-(N,N-dimethylcarbamoyl)-alpha-azalysine p-nitrophenyl ester (Dmc-azaLys-ONp). The enzyme kinetics are consistent with the minimum three-step catalytic mechanism of serine proteinases, the rate-limiting step being represented by the deacylation process. Bovine beta-trypsin kinetics are modulated by the acid-base equilibrium of the His57 catalytic residue (pKa approximately 6.9). Dmc-azaOrn-ONp and Dmc-azaLys-ONp bind stoichiometrically to the serine proteinase active site, and allow the reliable determination of the active enzyme concentration between 1.0 x 10-6 M and 3.0 x 10-4 M. The affinity and the reactivity for Dmc-azaOrn-ONp (expressed by Ks and k+2/Ks, respectively) of the serine proteinases considered are much lower than those for Dmc-azaLys-ONp. The very different affinity and reactivity properties for Dmc-azaOrn-ONp and Dmc-azaLys-ONp have been related to the different size of the ornithine/lysine side chains, and to the ensuing different positioning of the active-site titrants upon binding to the enzyme catalytic centre (i.e. to P1-S1 recognition). These data represent the first detailed comparative investigation on the catalytic properties of serine proteinases towards an ornithine derivative (i. e. Dmc-azaOrn-ONp).

Nitric oxide inhibits falcipain, the Plasmodium falciparum trophozoite cysteine protease

Nitric oxide (NO) is a pluripotent regulatory molecule possessing, among others, an antiparasitic activity. In the present study, the inhibitory effect of NO on the catalytic activity of falcipain, the papain-like cysteine protease involved in Plasmodium falciparum trophozoite hemoglobin degradation, is reported. In particular, NO donors S-nitrosoglutathione (GSNO), (+/-)-(E)-p6ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenami de (NOR-3), 3-morpholinosydnonimine (SIN-1), and sodium nitroprusside (SNP) inhibit dose-dependently the falcipain activity present in the P. falciparum trophozoite extract, this effect likely attributable to S-nitrosylation of the Cys25 catalytic residue. The results represent a new insight into the modulation mechanism of falcipain activity, thereby being relevant in developing new strategies for inhibition of the P. falciparum life cycle.

Structural determinants of trypsin affinity and specificity for cationic inhibitors

The binding free energies of four inhibitors to bovine beta-trypsin are calculated. The inhibitors use either ornithine, lysine, or arginine to bind to the S1 specificity site. The electrostatic contribution to binding free energy is calculated by solving the finite difference Poisson-Boltzmann equation, the contribution of nonpolar interactions is calculated using a free energy-surface area relationship and the loss of conformational entropy is estimated both for trypsin and ligand side chains. Binding free energy values are of a reasonable magnitude and the relative affinity of the four inhibitors for trypsin is correctly predicted. Electrostatic interactions are found to oppose binding in all cases. However, in the case of ornithine- and lysine-based inhibitors, the salt bridge formed between their charged group and the partially buried carboxylate of Asp189 is found to stabilize the complex. Our analysis reveals how the molecular architecture of the trypsin binding site results in highly specific recognition of substrates and inhibitors. Specifically, partially burying Asp189 in the inhibitor-free enzyme decreases the penalty for desolvation of this group upon complexation. Water molecules trapped in the binding interface further stabilize the buried ion pair, resulting in a favorable electrostatic contribution of the ion pair formed with ornithine and lysine side chains. Moreover, all side chains that form the trypsin specificity site are partially buried, and hence, relatively immobile in the inhibitor-free state, thus reducing the entropic cost of complexation. The implications of the results for the general problem of recognition and binding are considered. A novel finding in this regard is that like charged molecules can have electrostatic contributions to binding that are more favorable than oppositely charged molecules due to enhanced interactions with the solvent in the highly charged complex that is formed.

The T-knot motif revisited

The T-knot scaffold, a disulphide-reinforced structural motif shared by several proteins with very different biological functions, has been defined as 'a stretch of the protein chain which comprises two strands of a beta-sheet and three loops, knotted by two disulphides into the shape of the letter T'. In this communication we show that the presence of a central beta-sheet is not a required structural feature for proteins sharing the T-knot topology. Moreover, superposition of the three-dimensional structures of representative members of the T-knot family highlights a common and structurally well-defined core, formed by the two knotted disulphides, substituting for a larger residue-based hydrophobic core. These results suggest that folding and stability of the T-knot scaffold mainly depend on the geometry of the two knotted disulphides and on the loop length, and that the secondary structure elements are not a prerequisite for motif formation. Accordingly, a redefinition of the T-knot motif is proposed.

Stabilization of the T-state of ferrous human adult haemoglobin by chlorpromazine and trifluoperazine

In the present study, the effect of the neuroleptics chlorpromazine (2-chloro-N,N-dimethyl-10H-phenothiazine-10-propanamine) and trifluoperazine {10-[3-(4-methylpiperazin-l-yl)-propyl]-2-trifluoromethyl)-10-H- [phenothiazine}-10H-phenothiazine¿ on the EPR-spectroscopic properties of ferrous human adult nitrosylated haemoglobin (HbNO) is reported. Addition of the two drugs to HbNO shifted the conformational equilibrium from the high- to the low-affinity form of the ligated tetramer, as observed for 2,3-D-glycerate bisphosphate, the physiological modulator of haemoglobin action. The effect of chlorpromazine and trifluoperazine on the EPR-spectroscopic properties of HbNO was enhanced by inositol hexakisphosphate. The binding of neuroleptics to ferrous human adult haemoglobin may represent an important undesirable side effect. In fact, oxygen affinity for ferrous human adult haemoglobin decreases on increasing chlorpromazine and trifluoperazine concentration. In addition, red blood cells may act as neuroleptic scavengers.

Direct effect of temperature on the catalytic activity of nitric oxide synthases types I, II, and III

The effect of temperature (between 5.0 and 45.0 degrees C) on the catalytic activity of nitric oxide synthases types I, II, and III (NOS-I, NOS-II, and NOS-III, respectively) has been investigated, at pH 7.5. The value of V(max) for NOS-I activity increases from 1.8 x 10(1) pmol min(-1) mg(-1), at 5.0 degrees C, to 1.8 x 10(2) pmol min(-1) mg(-1), at 45.0 degrees C; on the other hand, the value of K(m) (=4.0 x 10(-6) M) is temperature independent. Again, the value of V(max) for NOS-II activity increases from 8.0 pmol min(-1) mg(-1), at 7.0 degrees C, to 5.4 x 10(1) pmol min(-1) mg(-1), at 40.0 degrees C, the value of K(m) (=1.8 x 10(-5) M) being unaffected by temperature. Temperature exerts the same effect on NOS-I and NOS-II activity, as shown by the same values of DeltaH(V(max)) (=4.2 x 10(1) kJ mol(-1)), DeltaH(K(m)) (=0 kJ mol(-1)), and DeltaH((V(max))(/K(m))()) (=4.2 x 10(1) kJ mol(-1)). On the contrary, the value of K(m) for NOS-III activity decreases from 3.8 x 10(-5) M, at 10.0 degrees C, to 1.6 x 10(-5) M, at 40.0 degrees C, the value of V(max) (=6.8 x 10(1) pmol min(-1) mg(-1)) being temperature independent. Present results indicate that temperature influences directly NOS-I and NOS-II activity independently of the substrate concentration, the values of K(m) being temperature independent. However, when l-arginine level is higher than 2 x 10(-4) M, as observed under in vivo conditions, NOS-III activity is essentially unaffected by temperature, the substrate concentration exceeding the value of K(m). As a whole, although further studies in vivo are needed, these observations seem to have potential physiopathologic implications.

Anticooperative ligand binding properties of recombinant ferric Vitreoscilla homodimeric hemoglobin: a thermodynamic, kinetic and X-ray crystallographic study

Thermodynamics and kinetics for cyanide, azide, thiocyanate and imidazole binding to recombinant ferric Vitreoscilla sp. homodimeric hemoglobin (Vitreoscilla Hb) have been determined at pH 6.4 and 7.0, and 20.0 degrees C, in solution and in the crystalline state. Moreover, the three-dimensional structures of the diligated thiocyanate and imidazole derivatives of recombinant ferric Vitreoscilla Hb have been determined by X-ray crystallography at 1.8 A (Rfactor=19.9%) and 2.1 A (Rfactor=23.8%) resolution, respectively. Ferric Vitreoscilla Hb displays an anticooperative ligand binding behaviour in solution. This very unusual feature can only be accounted for by assuming ligand-linked conformational changes in the monoligated species, which lead to the observed 300-fold decrease in the affinity of cyanide, azide, thiocyanate and imidazole for the monoligated ferric Vitreoscilla Hb with respect to that of the fully unligated homodimer. In the crystalline state, thermodynamics for azide and imidazole binding to ferric Vitreoscilla Hb may be described as a simple process with an overall ligand affinity for the homodimer corresponding to that for diligation in solution. These data suggest that the ligand-free homodimer, observed in the crystalline state, is constrained in a low affinity conformation whose ligand binding properties closely resemble those of the monoligated species in solution. From the kinetic viewpoint, anticooperativity is reflected by the 300-fold decrease of the second-order rate constant for cyanide and imidazole binding to the monoligated ferric Vitreoscilla Hb with respect to that for ligand association to the ligand-free homodimer in solution. On the other hand, values of the first-order rate constant for cyanide and imidazole dissociation from the diligated and monoligated derivatives of ferric Vitreoscilla Hb in solution are closely similar. As a whole, ligand binding and structural properties of ferric Vitreoscilla Hb appear to be unique among all Hbs investigated to date.

Cyanide binding to Lucina pectinata hemoglobin I and to sperm whale myoglobin: an x-ray crystallographic study

The x-ray crystal structures of the cyanide derivative of Lucina pectinata monomeric hemoglobin I (L. pectinata HbI) and sperm whale (Physeter catodon) myoglobin (Mb), generally taken as reference models for monomeric hemoproteins carrying hydrogen sulfide and oxygen, respectively, have been determined at 1.9 A (R-factor = 0. 184), and 1.8 A (R-factor = 0.181) resolution, respectively, at room temperature (lambda = 1.542 A). Moreover, the x-ray crystal structure of the L. pectinata HbI:cyanide derivative has been studied at 1.4-A resolution (R-factor = 0.118) and 100 K (on a synchrotron source lambda = 0.998 A). At room temperature, the cyanide ligand is roughly parallel to the heme plane of L. pectinata HbI, being located approximately 2.5 A from the iron atom. On the other hand, the crystal structure of the L. pectinata HbI:cyanide derivative at 100 K shows that the diatomic ligand is coordinated to the iron atom in an orientation almost perpendicular to the heme (the Fe-C distance being 1.95 A), adopting a coordination geometry strictly reminescent of that observed in sperm whale Mb, at room temperature. The unusual cyanide distal site orientation observed in L. pectinata HbI, at room temperature, may reflect reduction of the heme Fe(III) atom induced by free radical species during x-ray data collection using Cu Kalpha radiation.