Isolation and characterization of nitrogenase MoFe protein from the mutant strain pHK17 of Klebsiella pneumoniae in which the two bridging cysteine residues of the P-clusters are replaced by the non-coordinating amino acid alanine

Nitrogenase MoFe protein (Kp1) from the mutant strain pHK17 or Klebsiella pneumoniae has been purified to give three catalytically active fractions. In this mutant, each of the two bridging cysteine ligands to the P-clusters, alpha-Cys-89 and beta-Cys-94, has been replaced by a non-coordinating residue, alanine. SDS/PAGE and earlier native gels showed that the three fractions retained the normal alpha 2 beta 2 tetrameric form of wild-type Kp1; therefore we conclude that in each of the fractions the subunits are folded differently, thus resulting in different surface charges and allowing separation of the fractions on ion-exchange chronatography. Earlier EPR and magnetic CD data had shown that the mutant fractions contain P-clusters, and thus the mutated residues are not as essential for maintaining the integrity of the P-clusters as they appear from the X-ray structure. The specific activity of each of the three fractions was less than that of wild-type Kp1, the most active fraction having only 50% of wild-type activity. No change in substrate specificity or in the relative distribution of electrons to various substrates was found. The relationship between ATP hydrolysis and substrate-reducing activity, the EPR spectra of the S = 3/2 spin state of the iron-molybdenum cofactor (FeMoco) and the pH profile of acetylene-reduction activities of the three fractions did not differ significantly from those exhibited by wild-type Kp1. The specific activities of the three mutant fractions and of wild-type Kp1 were linearly proportional to the intensity of the S = 3/2 EPR signal from the FeMoco centres. This implies that those molecules of the three mutant fractions and the wild-type protein that contain EPR-active FeMoco are fully active, i.e. that the Cys to Ala substitution of the P-cluster ligands does not affect the specific activity of the protein. This in turn implies that the P-clusters are not directly associated with the rate-limiting step in enzyme turnover. We conclude that the lower specific activities of the mutant fractions are observed because the fractions are mixtures of species containing a full complement of FeMoco and P-clusters and species lacking some or all of these clusters. On the basis of the Mo contents and EPR spectroscopy of the mutant fractions, we propose that the loss of the P-clusters causes (i) the physical loss or inhibition of binding of some FeMoco; (ii) the EPR and catalytic inactivation of some FeMoco; and/or (iii) the incorporation of a FeMoco-like species into the FeMoco site of the mutant molecules.

Blood and Oral Fluid Cannabinoid Profiles of Frequent and Occasional Cannabis Smokers

Increased prevalence of cannabis consumption and impaired driving are a growing public safety concern. Some states adopted per se driving laws, making it illegal to drive with more than a specified ∆9-tetrahydrocannabinol (THC) blood concentration of THC in a biological fluid (typically blood). Blood THC concentrations decrease significantly (~90%) with delays in specimen collection, suggesting use of alternative matrices, such as oral fluid (OF). We characterized 10 cannabinoids' concentrations, including THC metabolites, in blood and OF from 191 frequent and occasional users by LC-MS-MS for up to 6 h after ad libitum smoking. Subjects self-titrated when smoking placebo, 5.9 or 13.4% THC cannabis. Higher maximum blood THC concentrations (Cmax) were observed in individuals who received the 5.9% THC versus the 13.4% THC plant material. In blood, the Cmax of multiple analytes, including THC and its metabolites, were increased in frequent compared to occasional users, whereas there were no significant differences in OF Cmax. Blood THC remained detectable (≥5 ng/mL) at the final sample collection for 14% of individuals who smoked either the 5.9% or 13.4% THC cigarette, whereas 54% had detectable THC in OF when applying the same cutoff. Occasional and frequent cannabis users' profiles were compared, THC was detectable for significantly longer in blood and OF from frequent users. Detection rates between frequent and occasional users at multiple per se cutoffs showed larger differences in blood versus OF. Understanding cannabinoid profiles of frequent and occasional users and the subsequent impact on detectability with current drug per se driving limits is important to support forensic interpretations and the development of scientifically supported driving under the influence of cannabis laws.

Effect of magnesium on plasma cholinesterase activity

Plasma cholinesterase activity levels were studied in 15 pregnant patients with preeclampsia before and after the administration of therapeutic doses of magnesium sulfate. Plasma cholinesterase activity was also studied in 15 healthy nonpregnant and 15 healthy pregnant women. The mean plasma cholinesterase activity level in pregnant patients with preeclampsia before and after the administration of magnesium sulfate was 179 +/- 26 and 176 +/- 39 units/ml, respectively. The healthy nonpregnant patients and healthy pregnant patients had a plasma cholinesterase activity level of 426 +/- 85 and 264 +/- 24 units/ml, respectively. Our data demonstrated that magnesium has no significant effect on plasma cholinesterase activity. Our data also confirm that there is a significant reduction in plasma cholinesterase activity in pregnant patients with preeclampsia compared with either healthy nonpregnant or healthy pregnant patients. We conclude that the low level of plasma cholinesterase activity is probably responsible for the prolonged action of succinylcholine in pregnant patients with preeclampsia receiving magnesium sulfate.

The influence of xenon, nitrous oxide and nitrogen on gas bubble expansion during cardiopulmonary bypass

BACKGROUND AND OBJECTIVE

Xenon may have favourable applications in the setting of cardiac surgery. Its advantages include a desirable haemodynamic profile as well as potential cardiac and neuroprotective properties. However, its low solubility may lead to enhanced diffusion into enclosed gas spaces. The purpose of this study was to compare the effects of xenon (Xe), nitrous oxide (N2O) and nitrogen (N2) on gas bubble size during cardiopulmonary bypass (CPB).

METHODS

Rats were randomized to receive 70% Xe, 26% oxygen (O2), 4% carbon dioxide (CO2) (xenon group); 70% N2O, 26% O2, 4% CO2 (nitrous oxide group) or 70% N2, 26% O2, 4% CO2 (nitrogen group) during 90 min of normothermic CPB. Small gas bubbles (300-500 microL; n = 12 per group) were injected into a bubble chamber on the venous side of the bypass circuit. After 10 min of equilibration, they were removed for volumetric analysis.

RESULTS

The increase in bubble size was 2 +/- 2% with nitrogen, 17 +/- 6% with xenon (P = 0.0192 vs. nitrogen) and 63 +/- 23% with nitrous oxide (P = 0.0001 vs. nitrogen). The nitrous oxide group had significantly increased bubble size compared to the xenon group (P = 0.0001).

CONCLUSIONS

During CPB, xenon anaesthesia produced a small increase in gas bubble size compared to nitrogen. Nitrous oxide resulted in significantly larger bubbles compared to both nitrogen and xenon.

Effect of pre-eclampsia on plasma cholinesterase activity

Plasma cholinesterase (PCHE) activity was determined using a colorimetric method in 11 healthy non-pregnant women, 11 healthy pregnant women at term, and 11 pre-eclamptic pregnant women at term. The mean plasma cholinesterase activities for healthy non-pregnant women, healthy pregnant women and pre-eclamptic pregnant women were 438 +/- 81,257 +/- 25 and 173 +/- 18 units . ml-1, respectively. Our data suggest that there is a significant reduction in plasma cholinesterase activity in preeclamptic pregnant women when compared to healthy non-pregnant (p less than 0.001) and healthy pregnant women (p less than 0.001).

Evidence on the role(s) of ATP in the mechanism of nitrogenase, from proton NMR relaxation studies on metal and nucleotide binding to the molybdenum-iron protein

Interactions between the molybdenum-iron protein (Kp1) of nitrogenase (reduced ferredoxin:dinitrogen oxidoreductase (ATP-hydrolysing,) EC 1.18.2.1) from Klebsiella pneumoniae and the divalent ions, Mn2+, Mg2+, Ca2+ and Ba2+, have been studied by monitoring the water proton NMR relaxation enhancement caused by the paramagnetism of Mn2+. We observed several binding sites for Mn2+, equivalent within experimental error (Kd = 209 +/- 23 microM), increasing in number from 1.0 to 2.9 per molecule in direct proportion to the specific activity of the protein. Metal binding sites on the MoFe protein are therefore essential to the enzymic function of nitrogenase. A maximum of four such sites is inferred for the fully active protein molecule. All manganese sites can alternatively bind the diamagnetic ions studied, the binding being one order-of-magnitude weaker (Kd = 2.2 +/- 0.3 mM for Mg2+; 1.6 +/- 0.2 mM for Ca2+; 3.4 +/- 0.3 mM for Ba2+), ATP and ADP form ternary complexes via Mn2+ with Kpl. The above data and other evidence on MgATP binding are discussed in terms of the site of hydrolysis of ATP during turnover and its possible bridging role between the two protein components of the enzyme.

Regulation of renal hemodynamics after protein feeding: effects of loop diuretics

These studies were designed to test the hypothesis that the renal vasodilation and increased glomerular filtration rate (GFR) after a high-protein meal are mediated by the tubuloglomerular feedback (TGF) mechanism. In eight chronically instrumented conscious dogs, a meal of raw beef (10 g/kg) caused GFR to increase from 66 +/- 5 to 90 +/- 7 ml/min and effective renal plasma flow (ERPF) to increase from 191 +/- 25 to 281 +/- 24 ml/min, while plasma alpha-amino N levels rose from 4.0 +/- 0.1 to 7.3 +/- 0.6 mg/dl. On another day the dogs were given an infusion of furosemide to block TGF, and fluid and salt losses were continuously replaced. Furosemide alone caused GFR to increase in most animals, although the average change did not reach statistical significance, and ERPF increased by 31%. Sodium excretion rose from 15 +/- 5 to 2,390 +/- 280 mueq/min, and urine flow rose from 1.17 +/- 0.22 to 20.5 +/- 2.4 ml/min. Autoregulatory capability was also abolished (autoregulatory index = 0.87 +/- 0.09 compared with 0.19 +/- 0.05 before furosemide). However, there was no significant change in GFR and ERPF after a subsequent meat meal in dogs receiving furosemide. On another day, some of the dogs were given another loop diuretic, ethacrynic acid, which caused no change in GFR, whereas its effects on ERPF, sodium excretion, and urine output were similar to those of furosemide. There were also no changes in GFR or ERPF after a meat meal during ethacrynic acid administration, despite normal increases in plasma alpha-amino N.(ABSTRACT TRUNCATED AT 250 WORDS)

Nucleotide binding by the nitrogenase Fe protein: a 31P NMR study of ADP and ATP interactions with the Fe protein of Klebsiella pneumoniae

Investigation of the interaction of MgADP- and MgATP2- with the Fe protein of Klebsiella pneumoniae nitrogenase by 31P NMR showed that the adenine nucleotides are reversibly bound in slow exchange with free nucleotides. Dissociation of the MgADP--Fe protein complex was slow enough to enable its isolation by gel filtration, thus permitting the assignment of resonances to bound nucleotides. Spectra of ADP bound to Kp2 were similar to spectra of ADP bound to the myosin motor domain. Oxidative inactivation of a Kp2-MgADP- complex with excess ferricyanide ion eliminated exchange between bound and free ADP, indicating that the intact iron sulphur cluster, located 20 A from the binding sites, is required for the reversible binding of MgADP-. A change in conformation on controlled oxidation of Kp2 with indigocarmine increased the chemical shift of the beta phosphate resonance of bound MgADP-. Both oxidized and reduced conformers were observed transiently in the absence of dithionite. The 31P resonances of both the beta and gamma phosphates of bound MgATP2- indicated major changes in environment and labilization of both groups on binding to the Fe protein. Highly purified Kp2 slowly hydrolysed ATP, resulting in mixtures of bound nucleotides. Partial occupation of Kp2 MgATP2--binding sites (N=1.9+/-0.2, Kd=145 microM) in concentrated protein solutions was demonstrated by flow dialysis. Scatchard plots of data for bound and free ligand obtained after equilibration with Kp2 were linear and no co-operative interactions were detected. We conclude that MgADP- stabilizes the oxidized Fe protein conformer and this conformation in turn triggers the dissociation of the Fe protein from the MoFe protein in the rate-limiting step of the overall process of dinitrogen reduction.

An evaluation of microdisks for dental identification

Twenty polyester dental identification microdisks were bonded to the surface of 20 extracted human mandibular molars and placed in 0.9% saline solution for 26 weeks, after which the teeth with bonded microdisks were embedded in bovine muscle tissue and incinerated for 11 minutes. Under the conditions of this study, 2 of the 20 polyester microdisks did not demonstrate deterioration and remained legible after storage in saline. The teeth and bonded microdisks did not appear to be affected by 11 minutes of incineration. A list of ideal characteristics for identification microdisks did proposed.

The inhibitory effect of metoclopramide on plasma cholinesterase activity

The in vitro effect of metoclopramide on plasma cholinesterase (PCHE) activity was studied to investigate a mechanism for metoclopramide-induced prolongation of succinylcholine action. The mean PCHE of the control samples was 0.86 +/- 0.02 unit.ml-1. PCHE activity in the presence of metoclopramide, at concentrations of 0.05, 0.10, 0.50, 1.0, 2.5 and 5.0 micrograms.ml-1, was reduced to 0.78 +/- 0.02, 0.69 +/- 0.04, 0.50 +/- 0.03, 0.39 +/- 0.02, 0.24 +/- 0.01 and 0.15 +/- 0.01 unit.ml-1, respectively. Our data demonstrated that PCHE activity was significantly depressed by metoclopramide at all concentrations studied (p less than 0.001). Our data also show that the concentration of metoclopramide required to inhibit 50 per cent of PCHE activity (I50) was 0.8 micrograms.ml-1 (2.4 x 10(-6) M). We recommend caution when succinylcholine and or ester type local anaesthetics are administered to patients who are also receiving metoclopramide, especially in high doses.

Xylazine enhances porcine myometrial contractility in vitro: possible involvement of alpha 2-adrenoceptors and Ca2+ channels

The effects of xylazine on porcine myometrial contractility were studied in vitro using uterine strips to determine the alpha 2-adrenergic influences during the diestrous stage of the estrous cycle. Xylazine (10(-8)-10(-5) M) caused a dose-dependent increase in the amplitude of myometrial contractility. The alpha 2-adrenoceptor antagonists idazoxan and yohimbine (10(-8)-10(-6) M) blocked the effects of xylazine in a dose-dependent manner. Yohimbine was approximately 10 times more potent than idazoxan in this regard. In contrast, an alpha 1-adrenoceptor antagonist prazosin (10(-7) and 10(-6) M) did not block the xylazine-induced increase in myometrial contractility, but a higher dose of prazosin (10(-5) M) did reduce the effects of xylazine. When the porcine uterine strips were pretreated with Ca2(+)-free Tyrod's solution or verapamil, a Ca2+ channel blocker, the effects of xylazine on myometrial contractility were completely abolished, whereas those of carbachol were only moderately reduced. The results suggest that the xylazine-induced myometrial contractility is mediated by alpha 2-adrenoceptors and that this effect is mediated, at least in part, by Ca2+ channels, whereas the effect of carbachol is attributed to an increase in both Ca2+ entry and release of Ca2+ from intracellular pools.

High frequency jet ventilation in intensive care--a review of 63 patients

High frequency jet ventilation has been used clinically in this unit for over 2 years. During this time we have treated 63 intensive care patients for whom the mean duration of ventilatory support was 3.4 days, which represents more than 5000 patient hours in total, with the Penlon Bromsgrove humidified jet ventilator. The series comprises a wide variety of general intensive care patients; a review of these cases is presented.

Demonstration of ignition radiation temperatures in indirect-drive inertial confinement fusion hohlraums

We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of T(RAD)=300 eV and a symmetric implosion to a 100 μm diameter hot core.

Synthesis and toxicity of some metabolites of the microbial degradation of synthetic naphthenic acids

Some ill-defined carboxylic acids, termed 'naphthenic acids' (NA), are best known as important constituents of the >720billionlitres of process-affected water associated with the expanding oil sands industries. Other NA are components of some immature and biodegraded crude oils and these may enter the environment via produced water discharges from oil production platforms. Yet others are used as biocides and in the manufacture of steel radial tyres and these may also enter the environment through disposal and/or weathering. The environmental fate of NA, including the mechanisms of biodegradation, therefore needs to be better understood. In order to better elucidate such mechanisms, previously we studied the biodegradation in the laboratory of some alkylcyclohexylbutanoic synthetic NA. However, we could only tentatively identify the metabolites produced. In the present study we report the synthesis and characterisation of six alkylcyclohexylethanoic NA. Each was characterised by gas chromatography-mass spectrometry (GC-MS; trimethylsilyl esters) and we show by co-chromatography that these were indeed the metabolites. Also, a preferential degradation of the trans- isomers was revealed. Assessment of the toxicity of the synthetic NA (Microtox assay), revealed that the relative toxicity of the alkylcyclohexylbutanoic acids was reduced by biotransformation to the alkylcyclohexylethanoic acids, as observed recently for the corresponding aromatic acids. Very recent studies have shown that at least one commercial NA mixture contains cyclohexylbutanoic and alkylcyclohexylethanoic acids, suggesting that the biotransformation of the acids studied herein may be quite relevant to the environmental fate of such acids. A similar study of the acid extractables of one oil sands process-affected water sample suggests that the synthetic acids may be less good 'models' for oil sands NA. The consortia of microbes present in oil sands process-affected water may also be different to those used herein. However, the heterogeneity of oil sands process water is well-known and further detailed studies will need to be made in order to establish whether degradation of oil sands NA proceeds by beta oxidation as observed for the acids herein, or whether the oil sands acids are more resistant to bioremediation.

Long-time spectral and intensity characteristics of esophageal speech

Long-time spectral characteristics and distributional properties of speech intensity produced by esophageal speakers were measured and compared with those of normal speakers. Substantial differences were observed in the distributional properties of speech intensity produced by normal and esophageal talkers. On the average, esophageal speech was about 10 dB less intense than normal speech. In addition, the average long-time spectrum for esophageal speech was characterized by a flattened spectral envelope. Other spectral differences between esophageal and normal speech were found and interpreted in terms of the known variations in voice and speech production of these two divergent forms of oral communication.

Lithium in the mating response and cell cycle of Saccharomyces cerevisiae

Studies with Li+, an inhibitor of phosphoinositide metabolism, demonstrated that an early response of Saccharomyces cerevisiae to a-factor pheromone was negatively affected by this cation. This was monitored by the production of beta-galactosidase from a reporter construct containing the promoter region of the yeast STE3 gene and the coding region of the E. coli LacZ gene. Growth and progression through the cell cycle were also affected by Li+ and analysis of budded/unbudded ratios revealed that Li+ caused yeast cells to arrest in G1. These data provide support for the role of inositol phosphates in the mating response and cell cycle of Saccharomyces cerevisiae.

Regional anaesthesia for surgery of the forearm and hand. A technique of combined supraclavicular and discrete blocks

Eighty patients who presented for surgery of the forearm or hand were allocated randomly to one of two groups. In Group A, surgery was performed under supraclavicular brachial plexus block only; a mixture of equal parts of prilocaine 1% and bupivacaine 0.5% without adrenaline was used. In Group B, supraclavicular brachial plexus block was performed using prilocaine 1% alone, but in addition discrete nerve blocks were performed at elbow level using 0.5% bupivacaine without adrenaline. Patients in Group B had a significantly shorter duration of unwanted postoperative motor blockade and a significantly longer duration of postoperative analgesia (p less than 0.005).

Reduction of cyclopropene by NifV- and wild-type nitrogenases from Klebsiella pneumoniae

The nitrogenase from wild-type Klebsiella pneumoniae reduces cyclopropene to cyclopropane and propene in the ratio 1:2 at pH 7.5. We show in this paper that the nitrogenase from a nifV mutant of K. pneumoniae also reduces cyclopropene to cyclopropane and propene, but the ratio of products is now 1:1.4. However, both nitrogenases exhibit the same Km for cyclopropene (2.1 x 10(4) +/- 0.2 x 10(4) Pa), considerably more than the Km for the analogous reaction with Azotobacter vinelandii nitrogenase under the same conditions (5.1 x 10(3) Pa). Analysis of the data shows that the different product ratio arises from the slower production of propene compared with cyclopropane by the mutant nitrogenase. During turnover, both nitrogenases use a large proportion of the electron flux for H2 production. CO inhibits the reduction of cyclopropene by both K. pneumoniae proteins, but the mutant nitrogenase exhibits 50% inhibition at approx. 10 Pa, whereas the corresponding value for the wild-type nitrogenase is approx. 110 Pa. However, H2 evolution by the mutant enzyme is much less affected than is cyclopropene reduction. CO inhibition of cyclopropene reduction by the nitrogenases coincides with a relative increase in H2 evolution, so that in the wild-type (but not the mutant) the electron flux is approximately maintained. The cyclopropane/propene production ratios are little affected by the presence of CO within the pressure ranges studied at least up to 50% inhibition.

Nitrogenase of Klebsiella pneumoniae. Water proton NMR relaxation studies on the binding of divalent metal ions and nucleotides to the iron protein

Interactions between the iron protein, Kp2, of nitrogenase manganese ions, magnesium ions, and the nucleotides ATP or ADP, have been studied in aqueous solution by monitoring the water proton NMR relaxation rate enhancement caused by Mn2+. Binding of Mn2+ to a molecule of Kp2 occurs at four sites, indistinguishable within experimental error, having a Kd = 350 +/- 50 micron. The Mn2+ - Kp2 complex has a low characteristic enhancement (epsilonb = 6 +/- 0.5). All four sites can alternatively bind Mg2+, not necessarily with the same dissociation constant, but with a mean Kd = 1.7 +/- 0.3 mM. Ternary complexes with the configuration EMS or (formula: see text) are formed between Kp2, Mn2+ and nucleotide (ATP or ADP). The ternary complexes with Mg2+ in place of Mn2+ probably have the latter configuration. A novel treatment of enhancement data (a 'high metal' approximation) is given.

Energy transduction by nitrogenase: binding of MgADP to the MoFe protein is dependent on the oxidation state of the iron-sulphur 'P' clusters

Hydrolysis of MgATP to MgADP is essential for nitrogenase action. There is good evidence for binding of both nucleotides to the Fe protein of nitrogenase, but data indicating their binding to the MoFe protein have been controversial [see Miller and Eady (1989) Biochem. J. 263, 725-729]. The binding of MgADP to the MoFe protein of nitrogenase of Klebsiella pneumoniae was investigated by non-equilibrium gel-filtration column methods. No binding of MgADP to the dithionite-reduced protein could be detected. Treatment of the MoFe protein with phenosafranine [midpoint potential (Em) -270 mV] did not affect the activity, and oxidized the 'P' clusters but not the iron-molybdenum cofactor (FeMoco) centres. This oxidized species bound 3.9 mol of MgADP with a binding pattern characteristic of low rates of ligand dissociation. These observations suggest that the variability in published data on nucleotide binding to the MoFe protein is related to poor control of the protein oxidation level. Our data, coupled with the observation that 'P' clusters become oxidized during reduction of N2 [Lowe, Fisher and Thorneley (1993) Biochem. J., in the press], led us to propose that the ADP binding sites are transiently filled during enzyme turnover by hydrolysis of ATP originally bound to the Fe protein, and that hydrolysis occurs on a bridging site on the MoFe-Fe-protein complex.

Laryngeal airway resistance in cleft palate children with complete and incomplete velopharyngeal closure

OBJECTIVE

This study investigated the effect of velopharyngeal insufficiency on aerodynamic measures of laryngeal function in children with cleft palate.

DESIGN

Data were analyzed using analysis of covariance. The independent variable was velopharyngeal closure, and the dependent variables were laryngeal resistance, laryngeal airflow, and transglottal pressure. Age and gender were covariates.

SETTING

The data were collected at The Craniofacial Center, University of Illinois, a tertiary health care center located in Chicago.

PATIENTS

Thirty-six children with cleft palate were recruited from among the patients at The Craniofacial Center. Ten children with velopharyngeal areas >5 mm2 during oral speech were placed in the incomplete closure group, while 26 children with areas <1 mm2 were placed in the complete closure group.

OUTCOME MEASURES

The three dependent variables (transglottal pressure, transglottal airflow, and laryngeal resistance) were measured.

RESULTS

Laryngeal resistance and transglottal pressure were significantly higher, and transglottal airflow was significantly lower in the group with complete closure.

CONCLUSIONS

In summary, cleft palate patients with complete velopharyngeal closure exhibited higher laryngeal resistances than those with incomplete closure.