Assembly of a [2Fe-2S]2+ cluster in a molecular variant of Clostridium pasteurianum rubredoxin

The rubredoxin from Clostridium pasteurianum contains a single iron atom bound to the polypeptide chain by cysteines 6, 9, 39, and 42. The C42A variant of this protein has been prepared by site-directed mutagenesis and heterologous expression of the gene in Escherichia coli. The mutated protein was found to contain an unexpected chromophore that has been characterized by a variety of techniques. UV-visible absorption and resonance Raman spectra were strongly reminiscent of those of [2Fe-2S] proteins. Mössbauer spectra of the oxidized chromophore isolated in oxygen-free conditions indicated low-temperature diamagnetism resulting from antiferromagnetically coupled high-spin ferric ions. Analysis of X-ray absorption fine structure spectra yielded an Fe-Fe distance of 2.68 A. Colorimetric assays of iron and inorganic sulfide showed that the two elements are present in a 1:1 ratio. Electrospray-ionization mass spectra displayed a major component at M = 6190 Da, i.e. the molecular mass of the C42A apoprotein plus two atomic masses of iron and two atomic masses of sulfur. Taken together, these data show that a mere point mutation allows the stabilization of a binuclear [2Fe-2S] cluster in a protein that normally accommodates a mononuclear Fe(Scys)4 site. Assembly of a [2Fe-2S] cluster may occur because rubredoxin assumes a similar fold around its metal center as the [2Fe-2S] Rieske protein. Alternatively, a more extensive structural rearrangement of the polypeptide chain of the C42A rubredoxin variant may be considered as well.

Reproducibility of the HERITAGE Family Study intervention protocol: drift over time

PURPOSE

The primary goal of the HERITAGE Family Study was to document the role of the genotype in the response to aerobic exercise training. Toward this end, nuclear families were enrolled in a 20-week exercise training program, with a large variety of tests performed before and after the training. Since study drift has the potential to adversely affect the results, reproducibility and potential bias over six consecutive 4-month periods were examined for selected test.

METHODS

Intraclass correlations (ICC), technical errors (TE), coefficients of variation within subject (CV), and means were calculated with use of the pretraining test results for each of the six time periods. To check for homogeneity, hypothesis tests were performed on the intraclass correlations and means. If homogeneity was not found across all six periods, further tests were performed to assess differences between pairs of time periods.

RESULTS

There was little evidence for real drifts in reproducibility, with most tests having ICCs of 0.8 or better. Only a few tests showed any change over time, and in no case was there evidence of a systematic drift in mean values.

CONCLUSIONS

Overall, the reproducibility of the HERITAGE Family Study tests and assays considered in this paper was found to be very good, with no evidence of any systematic drift over time.

Muscle-specific creatine kinase gene polymorphism and VO2max in the HERITAGE Family Study

This study examined the association between a DNA polymorphism in the muscle-specific creatine kinase (CKMM) gene and VO2max in the sedentary state, as well as its response (deltaVO2max) to a standardized 20-wk endurance training program. The subjects were 160 biologically unrelated Caucasian parents (80 women, 80 men) and 80 biologically unrelated adult offspring of the HERITAGE Family Study. The CKMM polymorphism was detected by PCR and digestion with the NcoI restriction enzyme. VO2max was measured during maximal cycle ergometer tests. VO2max was 2119 +/- 45 mL x min(-1) (mean +/- SE) or 26 +/- 0.4 mL x kg(-1) x min(-1). Both sexes had a significant (P < 0.05) increase in the deltaVO2max (women = 283 +/- 20 mL x min[-1] and men = 363 +/- 25 mL x min[-1]). Allele and genotype frequencies were not significantly different (P > 0.05) between sexes. Age and sex adjusted VO2max was significantly (P = 0.007) associated with the CKMM genotype in the parents, whereas no association (P > 0.05) was observed in the offspring. DeltaVO2max values adjusted for age, sex, VO2max, and body mass were characterized by genotype differences in both parents (P = 0.0004) and offspring (P = 0.0025). A significantly (P < 0.05) lower deltaVO2max to endurance training was detected in both parents and offspring homozygotes for the rare allele. The genotype accounted for at least 9% of the variance in deltaVO2max. These results indicate that the NcoI polymorphism in the 3' untranslated region of the muscle-specific creatine kinase gene is associated with the deltaVO2max to endurance training.

Specific interaction of the [2Fe-2S] ferredoxin from Clostridium pasteurianum with the nitrogenase MoFe protein

Putative physiological partners of the [2Fe-2S] ferredoxin from Clostridium pasteurianum have been searched by running crude soluble extracts of this bacterium through an affinity column to which the [2Fe-2S] ferredoxin had been covalently bound. Subsequent washing of the column with buffers of increasing ionic strength revealed a strong and specific interaction of the ferredoxin with the MoFe protein of nitrogenase. This interaction was further investigated by performing cross-linking experiments with mixtures of the two purified proteins in solution. Analysis of the reactions by SDS-polyacrylamide gel electrophoresis evidenced only two covalently linked products. These were identified by N-terminal sequencing as the alpha and beta subunits of the MoFe protein, each cross-linked to a single polypeptide chain of the ferredoxin. This result, taking into account the dimeric structure of the ferredoxin in solution, strongly suggests an interaction of the ferredoxin with the MoFe protein at a site contributed to by both subunits of the MoFe protein. The ionic strength dependence of the interaction evidenced by affinity chromatography was confirmed in the cross-linking reactions, and its specificity was assessed by showing that no cross-linking occurred when the [2Fe-2S] C. pasteurianum ferredoxin was denatured or replaced by spinach ferredoxin or by clostridial rubredoxin, or when the MoFe protein from C. pasteurianum was either inactivated or replaced by its counterpart from Azotobacter vinelandii. It has also been observed that the ferredoxin inhibits cross-linking between the nitrogenase Fe protein and the MoFe protein, which suggests overlapping binding sites of the ferredoxin and of the Fe protein on the MoFe protein. Cross-linking experiments implementing a number of molecular variants of the [2Fe-2S] C. pasteurianum ferredoxin demonstrated that glutamate residues 31, 34, and 38 are important contributors to the interaction with the MoFe protein.

Segregation analysis of abdominal visceral fat: the HERITAGE Family Study

A major gene hypothesis for abdominal visceral fat (AVF) level, both before and after adjustment for total body fat mass, was investigated in 86 white families who participated in the HERITAGE Family Study. In this study, sedentary families were tested for a battery of measures (baseline), endurance exercise trained for 20 weeks, and then remeasured again. The baseline measures reported here are unique in that the variance due to a potentially important environmental factor (activity level) was limited. AVF area was assessed at L4 to L5 by the use of computerized tomography scan, and total body fat mass was assessed with underwater weighing. For fat mass, a putative locus accounted for 64% of the variance, but there was no evidence of a multifactorial component (i.e., no polygenic and/or common familial environmental effects). For AVF area, both a major gene effect accounting for 54% of the variance and a multifactorial component accounting for 17% of the variance were significant. However, after AVF area was adjusted for the effects of total level of body fat, the support for a major gene was reduced. In particular, there was a major effect for fat mass-adjusted AVF area, but it was not transmitted from parents to offspring (i.e., the three transmission probabilities were equal). The importance of this study is twofold. First, these results confirm a previous study that suggested that there is a putative major locus for AVF and for total body fat mass. Second, the findings from the HERITAGE Family Study suggest that the factors underlying AVF area in sedentary families may be similar to those in the population at large, which includes both sedentary and active families. Whether the gene(s) responsible for the high levels of AVF area is the same as that which influences total body fat content remains to be further investigated.

Identification of an obesity quantitative trait locus on mouse chromosome 2 and evidence of linkage to body fat and insulin on the human homologous region 20q

Chromosomal synteny between the mouse model and humans was used to map a gene for the complex trait of obesity. Analysis of NZB/BINJ x SM/J intercross mice located a quantitative trait locus (QTL) for obesity on distal mouse chromosome 2, in a region syntenic with a large region of human chromosome 20, showing linkage to percent body fat (likelihood of the odds [LOD] score 3.6) and fat mass (LOD score 4.3). The QTL was confirmed in a congenic mouse strain. To test whether the QTL contributes to human obesity, we studied linkage between markers located within a 52-cM region extending from 20p12 to 20q13.3 and measures of obesity in 650 French Canadian subjects from 152 pedigrees participating in the Quebec Family Study. Sib-pair analysis based on a maximum of 258 sib pairs revealed suggestive linkages between the percentage of body fat (P < 0.004), body mass index (P < 0.008), and fasting insulin (P < 0.0005) and a locus extending approximately from ADA (the adenosine deaminase gene) to MC3R (the melanocortin 3 receptor gene). These data provide evidence that a locus on human chromosome 20q contributes to body fat and insulin in a human population, and demonstrate the utility of using interspecies syntenic relationships to find relevant disease loci in humans.

Physical activity, fibrinogen plasma level and gene polymorphisms in postmenopausal women

The relations between habitual physical activity (PA), fibrinogen gene polymorphisms and plasma fibrinogen were investigated in 191 postmenopausal women. Subjects who reported PA at least 4 times/week had lower fibrinogen level (3.19 g/l; 95% CI 3.10; 3.27) than women reporting PA 2-3 times/week (3.43 g/l; 3.29; 3.58) or sedentary subjects (3.64 g/l; 3.33; 3.94). There were no differences in plasma fibrinogen across the alpha-fibrinogen (RsaI, TaqI) or beta-fibrinogen (MnlI, BclI, HindIII) genotypes, the frequencies of which were in a Hardy-Weinberg equilibrium. An interaction between RsaI, which was in complete linkage disequilibrium with TaqI, and PA on plasma fibrinogen was observed, even after adjustments for BMI, smoking and medication (p = 0.024). Among women homozygous for the common RsaI allele, the physically most active had lower fibrinogen level (p <0.001) compared to the physically less active subjects. These results suggest that, in postmenopausal women, the relation between physical activity and plasma fibrinogen is modulated by genetic variation in the alpha-fibrinogen gene.

Influenza virus M1 protein binds to RNA through its nuclear localization signal

The RNA-binding activity of influenza A virus M1 protein was studied by cross-linking the protein to viral RNA followed by sequence analysis of the oligoribonucleotide bound to the protein as well as sequence analysis of the M1 peptide bound to the RNA. M1 was found to bind to RNA without any RNA sequence specificity, as verified in a series of filter-binding experiments using a large variety of nucleic acids including DNA. The peptide sequence that bound to the RNA was the RKLKR nuclear localization signal of M1. Site-specific mutagenesis of recombinant M1 showed that most of the basic residues in that region had to be mutated in order to inhibit RNA-binding. We also constructed an M1 mutant that no longer bound to RNA but which was still able to inhibit the in vitro transcription activity of isolated viral ribonucleoprotein, albeit to a lower extent. Mutation of the zinc-binding sequence had no effect on RNA-binding or transcription-inhibition activity.

Acute and chronic effects of exercise on leptin levels in humans

The acute (single bout of exercise) and chronic (exercise training) effects of exercise on plasma leptin were investigated in 97 sedentary adult men (n = 51) and women (n = 46) participating in the HERITAGE Family Study. Exercise training consisted of a standardized 20-wk endurance training program performed in the laboratory on a computer-controlled cycle ergometer. Maximal oxygen uptake, body composition assessed by hydrostatic weighing, and fasting insulin level were also measured before and after training. Pre- and posttraining blood samples were obtained before and after completion of a maximal exercise test on the cycle ergometer. Exercise training resulted in significant changes in maximal oxygen uptake (increase in both genders) and body composition (reduction of fat mass in men and increase in fat-free mass in women). There were considerable interindividual differences in the leptin response to acute and chronic effects of exercise, some individuals showing either increase or reduction in leptin, others showing almost no change. On average, leptin levels were not acutely affected by exercise. After endurance training was completed, leptin levels decreased significantly in men (from 4.6 to 3.9 ng/ml; P = 0.004) but not in women. However, after the training-induced changes in body fat mass were accounted for, the effects of exercise training were no longer significant. Most of the variation observed in leptin levels after acute exercise or endurance training appears to be within the confidence intervals of the leptin assay. We conclude that there are no meaningful acute or chronic effects of exercise, independent of the amount of body fat, on leptin levels in humans.

Probing the influence of mutations on the stability of a ferredoxin by mass spectrometry

Hydrogen/deuterium exchange, which depends on solvent accessibility, can be probed by mass spectrometry (MS) to get information on protein conformation or protein-ligand interaction. In this work, the conformational properties of the cyanobacterium Anabaena wild-type ferredoxin as well as of two single-site mutants (Phe 65 Ala and Arg 42 Ala) were studied. After incubation of the wild type and mutant proteins in deuterated water and quenching of the exchange at low pH, the proteins were rapidly digested at high enzyme-to-substrate ratio using immobilized pepsin, and the resulting peptides were characterized using ESI-MS. We have identified specific regions for which the H-bonding or solvent accessibility properties were perturbed by the mutations. These results show that this approach can provide local information on the influence of mutations, even for a highly structured protein like ferredoxin, and sometimes in regions distant from the mutation point.

Structure and assembly of the catalytic region of human complement protease C1r: a three-dimensional model based on chemical cross-linking and homology modeling

C1r is the modular serine protease responsible for autocatalytic activation of C1, the first component of the complement classical pathway. Its catalytic region is a noncovalent homodimer of two gamma-B monomers, each comprising two contiguous complement control protein (CCP) modules, IV and V [also known as short consensus repeats (SCRs)], a 15-residue intermediary segment, and the serine protease B domain. With a view to gain insight into domain-domain interactions within this region, fragment C1r (gamma-B)2, obtained by autolytic proteolysis of the active protease, was cross-linked with the water-soluble reagent 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide. Cross-linked species gamma-B intra and gamma-B inter, containing intra- and intermonomer cross-links, respectively, were isolated and then fragmented by CNBr cleavage and trypsin digestion. N-Terminal sequence and mass spectrometry analyses of the resulting cross-linked peptides allowed us to identify one intramonomer cross-link between Lys426 of module V and the C-terminal Asp688 of the serine protease B domain and one intermonomer cross-link between the N-terminal Gly280 of fragment gamma and Glu493 of the B domain. Three-dimensional homology modeling of the CCP modules IV and V and of the B domain was also performed. The complementary information provided by chemical cross-linking and homology modeling studies was used to construct a three-dimensional model of the gamma-B monomer, in which module V interacts with the serine protease on the side opposite to both the active site and the Arg446-Ile447 activation site. Also, a tentative three-dimensional model of the (gamma-B)2 dimer was built, indicating a loose "head to tail" association of the monomers, with the active sites facing opposite directions toward the outside of the dimer. The latter model is compared with available low-resolution structural data, and its functional implications are discussed in terms of the conformational changes occurring during C1r activation.

Variation in plasma fibrinogen over one year: relationships with genetic polymorphisms and non-genetic factors

We analyzed plasma fibrinogen level in relation to genetic polymorphisms in the alpha- and beta-fibrinogen gene loci. Furthermore, the association of other CVD risk markers with fibrinogen was studied twice, with a time interval of one year in 50 to 60 year old men (n = 183). DNA polymorphisms were detected by PCR and digestion with Taq I (alpha-fibrinogen), Hind III and Bcl I (beta-fibrinogen) restriction enzymes. The correlation coefficient between fibrinogen measurements was 0.48 (p < 0.001). Blood leucocytes and waist-to-hip circumference ratio were the strongest correlates of fibrinogen level in both examinations, and the changes in leucocyte count and plasma fibrinogen correlated positively (r = 0.40, p < 0.001). In Eastern Finnish men, the Taq I, Hind III or Bcl I restriction fragment length polymorphisms of the alpha- or beta-fibrinogen gene loci did not associate with fibrinogen level, either cross-sectionally or longitudinally.

Abdominal visceral fat is associated with a BclI restriction fragment length polymorphism at the glucocorticoid receptor gene locus

Several investigations have suggested that body fat distribution is influenced by nonpathologic variations in the responsiveness to cortisol. Genetic variations in the glucocorticoid receptor (GRL) could therefore potentially have an impact on the level of abdominal fat. A restriction fragment length polymorphism (RFLP) has previously been detected with the BclI restriction enzyme in the GRL gene identifying two alleles with fragment lengths of 4.5 and 2.3 kb. This study investigates whether abdominal fat areas measured by computerized tomography (CT) are associated with this polymorphism in 152 middle-aged men and women. The less frequent 4.5-kb allele was found to be associated with a higher abdominal visceral fat (AVF) area independently of total body fat mass (4.5/4.5 vs. 2.3/2.3 kb genotype; men: 190.7 +/- 30.1 vs. 150.7 +/- 33.3 cm2, p = 0.04; women: 132.7 +/- 37.3 vs. 101.3 +/- 34.5 cm2, p = 0.06). However, the association with AVF was seen only in subjects of the lower tertile of the percent body fat level. In these subjects, the polymorphism was found to account for 41% (p = 0.003) and 35% (p = 0.007), in men and women, respectively, of the total variance in AVF area. The consistent association between the GRL polymorphism detected with BclI and AVF area suggests that this gene or a locus in linkage disequilibrium with the BclI restriction site may contribute to the accumulation of AVF.

Reproducibility of anthropometric and body composition measurements: the HERITAGE Family Study

OBJECTIVE

To determine the reproducibility of anthropometric and body composition measures using the HERITAGE Family Study protocol.

DESIGN

Anthropometric and body composition measures were obtained on three separate days within a 3-wk period at each of the four HERITAGE Clinical Centers.

SUBJECTS

Sixty men and women representative of the HERITAGE subject population, 15 from each of four Clinical Centers.

MEASUREMENTS

Anthropometric measures included eight skinfolds, three girths and one length; and body composition measures included stature, mass, hydrostatic weight, residual volume, and body density, from which relative fat, fat mass and fat-free mass were estimated.

RESULTS

Reproducibility as determined by technical error, coefficient of variation, and intraclass correlations was very high for the total sample. For example, intraclass correlations for the total sample generally ranged from 0.95-0.99 for the anthropometric measures, and from 0.97-1.00 for the body composition measures. The results across Clinical Centers were in close agreement with each other and with the pooled data.

CONCLUSIONS

The reproducibility of anthropometric and body composition measures using the HERITAGE Family Study protocol is sufficiently high that it should be possible to detect small changes in any of these measures and to determine the genetic basis of these changes consequent to a 20 wk endurance training program.

Chemical synthesis and characterization of the epidermal growth factor-like module of human complement protease C1r

C1r is one of the two serine proteases of C1, the first component of complement, in which it is associated in a calcium-dependent manner to the homologous serine protease C1s. This interaction is mediated by the N-terminal region of C1r, which comprises a single epidermal growth factor (EGF)-like module containing the consensus sequence required for calcium binding, surrounded by two CUB modules. With a view to determine the structure of the EGF-like module of C1r and evaluate its contribution to calcium binding, this module [C1r(123-175)] was synthesized by automated solid-phase methodology using the Boc strategy. A first synthesis using the Boc-His(Z) derivative gave very low yield, due to partial deprotection of His residues leading to chain termination by acetylation, and to insertion of glycine residues. This could be circumvented by using the Boc-His(DNP) derivative and by condensation of appropriate glycine-containing segments. The synthetic peptide was efficiently folded under redox conditions to the species with three correct disulfide bridges, as determined by mass spectrometry and N-terminal sequence analyses of thermolytic fragments. The homogeneity of the synthetic peptide was assessed by reversed-phase HPLC and electrospray mass spectrometry. One-dimensional 1H NMR spectroscopic analysis provided evidence that the EGF-like module had a well defined structure, and was able to bind calcium with an apparent Kd of 10 mM. This value, comparable to that found for the isolated EGF-like modules of coagulation factors IX and X, is much higher than that measured for native C1r. As already proposed for factors IX and X, it is suggested that neighbouring module(s), most probably the N-terminal CUB module, contribute(s) to the calcium binding site.

Suggestive linkages between markers on human 1p32-p22 and body fat and insulin levels in the Quebec Family Study

A single-gene rodent mutation (diabetes) and a quantitative trait locus (dietary obese 1) mapped to the mid portion of mouse chromosome 4 have been related to obesity and/or insulin levels. Synteny relationships place their putative human homologs on 1p31 and 1p35-p31, respectively. In 137 sibships of adult brothers and sisters from the Québec Family Study, genetic linkages between seven microsatellite markers from 1p32-p22 and various obesity- and diabetes-related quantitative phenotypes were examined using single locus sibpair linkage analysis. Suggestive linkages were observed between markers D1S476 and body mass index (p = 0.05), fat mass (p = 0.02), the sum of six skinfolds (p = 0.02), the insulin area after an oral glucose tolerance test (p = 0.02), and between the neighboring marker D1S200 and body mass index (p = 0.03), and fat mass (p = 0.009). Suggestive linkages were also observed between the more telomeric markers D1S193 and body mass index (p = 0.03), and between the neighboring marker D1S197 and fasting insulin level (p = 0.05). No linkage was observed with the trunk to extremity skinfolds ratio. These linkages suggest that human homologs of the mouse diabetes or dietary obese 1 and/or other genes in this interval on chromosome 1 play a role in the regulation of body mass, body composition, and insulin levels, but not of subcutaneous fat distribution.

Association of -158 (C-->T) (XmnI) DNA polymorphism in G gamma-globin promoter with delayed switchover from fetal to adult hemoglobin synthesis

In this study, the effect of -158 (C-->T) (XmnI) polymorphism on the synthesis of fetal Hb and its G gamma component during the switchover from fetal to adult Hb was examined using cord blood samples from normal Caucasian term infants. The presence of -158(C-->T) mutation was determined by amplification of G gamma and A gamma-globin gene promoter fragments from the DNA isolated from cord blood samples, followed by XmnI restriction enzyme digestion. The syntheses of fetal and adult Hb in cord blood were measured by [3H]leucine incorporation in globin synthesis, separation of the globin polypeptides by HPLC, and scintillation counting of the fractions. The presence of -158(C-->T) substitution in the G gamma-globin promoter region was positively correlated with elevated synthesis of fetal Hb and its G gamma-globin component in term newborn infants and is associated with delayed switchover from fetal to adult Hb. In addition analysis of cord blood samples from 100 normal Caucasian French Canadian term infants revealed that the frequency of -158(C-->T) substitution in G gamma-promoter was 0.32.

Can immunoglobulin C(H)1 constant region domain modulate antigen binding affinity of antibodies?

Although the switch process is frequently associated with affinity maturation, the constant region is not assumed to play a role in Ag-Ab binding. In the present work, we demonstrate that two clonally related human monoclonal Igs sharing identical V(H) and V(L) sequences, but expressing different isotypes (IgA1kappa(PER) and IgG1kappa(PER)), bind tubulin with significantly different affinities. This difference was mainly accounted for by a disparity in the association rate constants. These results suggest that affinity maturation of this clone could be achieved through class switching in the absence of further somatic mutations. Since the differences observed were found at the Fab level, they also suggest a role for the C(H)1 domain in structuring the Ag-binding site into a more kinetically competent form.

The HERITAGE Family Study: quality assurance and quality control

The HERITAGE (HEalth, RIsk factors, exercise Training And GEnetics) Family Study is the first multicenter family clinical trial of its kind. Conducted by a consortium of five universities in the United States and Canada, the study has as its primary goal to document the role of the genotype in the cardiovascular, metabolic, and hormonal responses to aerobic exercise training. A comprehensive protocol was implemented at four Clinical Centers (CC) for the generation of data on sedentary subjects. This group included 450 caucasians from 90 nuclear families (father, mother, three children) and 200 black subjects from 40 to 100 family units over a 5-year period. The entire family was tested before and after a 20-week exercise training program. The fifth participating center, the Data Coordinating Center (DCC), is responsible for data management and data analysis. A Consortium Coordinating Center (CCC) responsible for the overall coordination and direction of the study was established at the Quebec CC. Quality assurance and quality control are jointly coordinated by the CCC and the DCC. A multicenter study of this magnitude requires careful standardization of all procedures and constant monitoring of quality control at all levels of operation. This report describes the quality assurance and quality control measures implemented in the HERITAGE Family Study, including some examples with real data.

The Trp64Arg mutation of the beta3 adrenergic receptor gene has no effect on obesity phenotypes in the Québec Family Study and Swedish Obese Subjects cohorts

The beta adrenergic system plays a key role in regulating energy balance through the stimulation of both thermogenesis and lipid mobilization in brown and white adipose tissues in human and various animal models. Recent studies have suggested that a missense Trp64Arg mutation in the beta3 adrenergic receptor (ADRB3) gene was involved in obesity and insulin resistance. We have investigated the effect of this mutation on obesity-related phenotypes in two cohorts: the Québec Family Study (QFS) and the Swedish Obese Subjects (SOS). In QFS, no association was found between this mutation and body mass index (BMI), body fat including abdominal visceral fat, resting metabolic rate, various diabetes and cardiovascular risk factors, and changes in body weight and body fat over a 12-yr period. With the exception of RMR (P = 0.04), no evidence of linkage was detected between the mutation and phenotypes of QFS based on sib-pair data. In SOS, the frequency of the Trp64Arg allele was not significantly different between nonobese and obese female subjects and no association was found between the mutation and body weight gain over time. These findings do not support the view that there is an association between the Trp64Arg mutation in the ADRB3 gene and obesity.

Inhibition by iodoacetamide and acetylene of the H-D-exchange reaction catalyzed by Thiocapsa roseopersicina hydrogenase

The kinetics of H-D isotope exchange catalyzed by the thermostable hydrogenase from Thiocapsa roseopersicina have been studied by analysis of the exchange between D2 and H2O. The pH dependence of the exchange reaction was examined between pH 2.5 and pH 11. Over the whole pH range, HD was produced at a higher initial velocity than H2, with a marked optimum at pH 5.5; a second peak in the pH profile was observed at around pH 8.5. The rapid formation of H2 with respect to HD in the D2/H2O system is consistent with a heterolytic cleavage of D2 into D+ and an enzyme hydride that can both exchange with the solvent. The H-D-exchange activity was lower in the H2/D2O system than in the D2/H2O system. The other reactions catalyzed by the hydrogenase, H2 oxidation and H2 evolution, are pH dependent; the optimal pH were 9.5 for H2 uptake and 4.0 for H2 production. Treatment of the active form of hydrogenase by iodoacetamide led to a slow and irreversible inhibition of the H-D exchange. When iodo[1-14C]acetamide was incubated with hydrogenase, the radioactive labeling of the large subunit was higher for the enzyme activated under H2 than for the inactive oxidized form. Cysteine residues were identified as the alkylated derivative by amino acid analysis. Acetylene, which inhibits H-D exchange and abolishes the Ni-C EPR signal, protected the enzyme from irreversible inhibition by iodoacetamide. These data indicate that iodoacetamide can reach the active site of the H2-activated hydrogenase from T. roseopersicina. This was not found to be the case with the seleno hydrogenase from Desulfovibrio baculatus (now Desulfomicrobium baculatus). Cysteine modification by iodoacetamide upon activation of the enzyme concomitant with loss of H-D exchange indicates that reductive activation makes at least one Cys residue of the active site available for alkylation.