Expression and kinetic characterization of variants of human beta 1 beta 1 alcohol dehydrogenase containing substitutions at amino acid 47

ADH1B, the adipocyte-enriched alcohol dehydrogenase, plays an essential, cell-autonomous role in human adipogenesis

Alcohol dehydrogenase 1B (ADH1B) is a primate-specific enzyme which, uniquely among the ADH class 1 family, is highly expressed both in adipose tissue and liver. Its expression in adipose tissue is reduced in obesity and increased by insulin stimulation. Interference with ADH1B expression has also been reported to impair adipocyte function. To better understand the role of ADH1B in adipocytes, we used CRISPR/Cas9 to delete ADH1B in human adipose stem cells (ASC). Cells lacking ADH1B failed to differentiate into mature adipocytes manifested by minimal triglyceride accumulation and a marked reduction in expression of established adipocyte markers. As ADH1B is capable of converting retinol to retinoic acid (RA), we conducted rescue experiments. Incubation of ADH1B-deficient preadipocytes with 9-cis-RA, but not with all-transretinol, significantly rescued their ability to accumulate lipids and express markers of adipocyte differentiation. A homozygous missense variant in ADH1B (p.Arg313Cys) was found in a patient with congenital lipodystrophy of unknown cause. This variant significantly impaired the protein's dimerization, enzymatic activity, and its ability to rescue differentiation in ADH1B-deficient ASC. The allele frequency of this variant in the Middle Eastern population suggests that it is unlikely to be a fully penetrant cause of severe lipodystrophy. In conclusion, ADH1B appears to play an unexpected, crucial and cell-autonomous role in human adipocyte differentiation by serving as a necessary source of endogenous retinoic acid.

Supersulfide catalysis for nitric oxide and aldehyde metabolism

Abundant formation of endogenous supersulfides, which include reactive persulfide species and sulfur catenated residues in thiols and proteins (supersulfidation), has been observed. We found here that supersulfides catalyze S-nitrosoglutathione (GSNO) metabolism via glutathione-dependent electron transfer from aldehydes by exploiting alcohol dehydrogenase 5 (ADH5). ADH5 is a highly conserved bifunctional enzyme serving as GSNO reductase (GSNOR) that down-regulates NO signaling and formaldehyde dehydrogenase (FDH) that detoxifies formaldehyde in the form of glutathione hemithioacetal. C174S mutation significantly reduced the supersulfidation of ADH5 and almost abolished GSNOR activity but spared FDH activity. Notably, Adh5C174S/C174S mice manifested improved cardiac functions possibly because of GSNOR elimination and consequent increased NO bioavailability. Therefore, we successfully separated dual functions (GSNOR and FDH) of ADH5 (mediated by the supersulfide catalysis) through the biochemical analysis for supersulfides in vitro and characterizing in vivo phenotypes of the GSNOR-deficient organisms that we established herein. Supersulfides in ADH5 thus constitute a substantial catalytic center for GSNO metabolism mediating electron transfer from aldehydes.

Role of Metabolism on Alcohol Preference, Addiction, and Treatment

Studies presented in this chapter show that: (1) in the brain, ethanol is metabolized by catalase to acetaldehyde, which condenses with dopamine forming salsolinol; (2) acetaldehyde-derived salsolinol increases the release of dopamine mediating, via opioid receptors, the reinforcing effects of ethanol during the acquisition of ethanol consumption, while (3) brain acetaldehyde does not influence the maintenance of chronic ethanol intake, it is suggested that a learned cue-induced hyperglutamatergic system takes precedence over the dopaminergic system. However, (4) following a prolonged ethanol deprivation, the generation of acetaldehyde in the brain again plays a role, contributing to the increase in ethanol intake observed during ethanol re-access, called the alcohol deprivation effect (ADE), a model of relapse behavior; (5) naltrexone inhibits the high ethanol intake seen in the ADE condition, suggesting that acetaldehyde-derived salsolinol via opioid receptors also contributes to the relapse-like drinking behavior. The reader is referred to glutamate-mediated mechanisms that trigger the cue-associated alcohol-seeking and that also contribute to triggering relapse.

Strong association between the 12q24 locus and sweet taste preference in the Japanese population revealed by genome-wide meta-analysis

The sweet taste preference of humans is an important adaptation to ensure the acquisition of carbohydrate nutrition; however, overconsumption of sweet foods can potentially lead to diseases such as obesity and diabetes. Although previous studies have suggested that interindividual variation of human sweet taste preference is heritable, genetic loci associated with the trait have yet to be fully elucidated. Here, we genotyped 12,312 Japanese participants using the HumanCore-12+ Custom BeadChip or the HumanCore-24 Custom BeadChip microarrays. The sweet taste preference of the participants was surveyed via an internet-based questionnaire, resulting in a five-point scale of sweet taste preference. The genome-wide meta-analysis of the Japanese participants revealed a strong association between the 12q24 locus and sweet taste preference scale (P = 2.8 × 10^-70). The lead variant rs671 is monoallelic in non-East Asian populations and is located in the aldehyde dehydrogenase (ALDH2) gene, encoding an enzyme involved in alcohol metabolism. The association between the minor allele of rs671 and sweet taste preference was attenuated by adjusting for alcohol drinking. The subgroup analysis showed that the effect of rs671 on sweet taste preference was greater in males than in females. In conclusion, we found an association between the 12q24 locus and sweet taste preference in the Japanese population, and showed that the adjustment for drinking habits attenuated the association. This novel genetic association may provide new clues to elucidate mechanisms determining sweet taste preferences.

Modeling of Human Hepatic and Gastrointestinal Ethanol Metabolism with Kinetic-Mechanism-Based Full-Rate Equations of the Component Alcohol Dehydrogenase Isozymes and Allozymes

Alcohol dehydrogenase (ADH) is the principal enzyme responsible for the metabolism of ethanol. Human ADH constitutes a complex family of isozymes and allozymes with striking variation in kinetic properties and tissue distribution. The liver and the gastrointestinal tract are the major sites for first-pass metabolism (FPM). The quantitative contributions of ADH isozymes and ethnically distinct allozymes to cellular ethanol metabolism remain poorly understood. To address this issue, kinetic mechanism and the steady-state full-rate equations for recombinant human class I ADH1A, ADH1B (including allozymes ADH1B1, ADH1B2, and ADH1B3), ADH1C (including allozymes ADH1C1 and ADH1C2), class II ADH2, and class IV ADH4 were determined by initial velocity, product inhibition, and dead-end inhibition experiments in 0.1 M sodium phosphate at pH 7.5 and 25 °C. Models of the hepatic and gastrointestinal metabolisms of ethanol were constructed by linear combination of the numerical full-rate equations of the component isozymes and allozymes in target organs. The organ simulations indicate that in homozygous ADH1B*1/*1 livers, a representative genotype among ethnically distinct populations due to high prevalence of the allele, major contributors at 1 to 10 mM ethanol are ADH1B1 (45% to 24%) and the ADH1C allozymes (54% to 40%). The simulated activities at 1 to 50 mM ethanol for the gastrointestinal tract (total mucosae of ADH1C*1/*1-ADH4 stomach and the ADH1C*1/*1-ADH2 duodenum and jejunum) account for 0.68%-0.76% of that for the ADH1B*1/*1-ADH1C*1/*1 liver, suggesting gastrointestinal tract plays a relatively minor role in the human FPM of ethanol. Based on the flow-limited sinusoidal perfusion model, the simulated hepatic K_m^app, V_max^app, and C_i at a 95% clearance of ethanol for ADH1B*1/*1-ADH1C*1/*1 livers are compatible to that documented in hepatic vein catheterization and pharmacokinetic studies with humans that controlled for the genotypes. The model simulations suggest that slightly higher or similar ethanol elimination rates for ADH1B*2/*2 and ADH1B*3/*3 individuals compared with those for ADH1B*1/*1 individuals may result from higher hepatocellular acetaldehyde.

FineMAV: prioritizing candidate genetic variants driving local adaptations in human populations

We present a new method, Fine-Mapping of Adaptive Variation (FineMAV), which combines population differentiation, derived allele frequency, and molecular functionality to prioritize positively selected candidate variants for functional follow-up. We calibrate and test FineMAV using eight experimentally validated "gold standard" positively selected variants and simulations. FineMAV has good sensitivity and a low false discovery rate. Applying FineMAV to the 1000 Genomes Project Phase 3 SNP dataset, we report many novel selected variants, including ones in TGM3 and PRSS53 associated with hair phenotypes that we validate using available independent data. FineMAV is widely applicable to sequence data from both human and other species.

Associations Between Genomic Variants in Alcohol Dehydrogenase Genes and Alcohol Symptomatology in American Indians and European Americans: Distinctions and Convergence

BACKGROUND

Higher rates of alcohol use disorders (AUD) have been observed in some Native American populations than other ethnic groups such as European Americans (EAs) in the United States. Previous studies have shown that variation in the alcohol dehydrogenase (ADH) genes may affect the risk for development of AUD and that the prevalence of these variants differs depending on the ancestral origins of a population.

METHODS

In this study, we assessed sequencing variants in the ADH genomic region (ADH1-7) and tested for their associations with AUD phenotypes in 2 independent populations: an American Indian (AI) community sample and an EA cohort from the San Francisco Family Alcohol Study. Association tests were conducted for both common and rare variants using sequencing data for 2 phenotypes: the number of alcohol-related life events and the count of alcohol dependence drinking symptoms. A regularized regression method was used to select the best set of ADH variants associated with phenotypes. Variance component model was incorporated in all analyses to leverage the admixture and relatedness.

RESULTS

Two variants near ADH4 and 2 near ADH1C exhibited significant associations with AUD in AIs; no variant was significant in EAs. Common risk variants in AIs were either absent from or much less frequent in EAs. The feature selection method selected mostly distinct yet often colocated subsets of ADH variants to be associated with AUD phenotypes between the 2 cohorts. In the rare-variant analyses, the only association was observed between the whole region and the alcohol-related life events in AIs.

CONCLUSIONS

Our results suggest that ADH variants, both common and rare, are more likely to impact risk for alcohol-related symptomatology in this AI population than in this EA sample, and ADH variants that might affect AUD are likely different but convergent on similar regions between the 2 populations.

Genetic variants in ALDH1B1 and alcohol dependence risk in a British and Irish population: A bioinformatic and genetic study

Alcohol is metabolized in the liver via the enzymes alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). Polymorphisms in the genes encoding these enzymes, which are common in East Asian populations, can alter enzyme kinetics and hence the risk of alcohol dependence and its sequelae. One of the most important genetic variants, in this regards, is the single nucleotide polymorphism (SNP) rs671 in ALDH2, the gene encoding the primary acetaldehyde metabolizing enzyme ALDH2. However, the protective allele of rs671 is absent in most Europeans although ALDH1B1, which shares significant sequence homology with ALDH2, contains several, potentially functional, missense SNPs that do occur in European populations. The aims of this study were: (i) to use bioinformatic techniques to characterize the possible effects of selected variants in ALDH1B1 on protein structure and function; and, (ii) to genotype three missense and one stop-gain, protein-altering, non-synonymous SNPs in 1478 alcohol dependent cases and 1254 controls of matched British and Irish ancestry. No significant allelic associations were observed between the three missense SNPs and alcohol dependence risk. The minor allele frequency of rs142427338 (Gln378Ter) was higher in alcohol dependent cases than in controls (allelic P = 0.19, OR = 2.98, [0.62–14.37]) but as this SNP is very rare the study was likely underpowered to detect an association with alcohol dependence risk. This potential association will needs to be further evaluated in other large, independent European populations.

Alcohol Dehydrogenase: An Autoantibody Target in Patients with Alcoholic Liver Disease

The link between alcohol consumption and liver disease is not direct and several factors including autoimmunity to hepatocyte components have been implicated. We have previously identified alcohol dehydrogenase (ADH) as an autoantigen in autoimmune liver disease and in a proportion of patients with alcoholic liver disease. The aim of the present study is to investigate the association between the presence of anti-ADH antibodies, alcohol consumption and severity of liver damage in alcoholic patients. The presence of antibodies to human ADH β2 and horse ADH was investigated in 108 patients with documented history of alcohol consumption and alcohol related liver disease, 86 being active alcohol abusers and 22 on sustained alcohol withdrawal, 39 with non-alcohol related disease and 22 normal subjects.

Antibodies to either ADH form were more frequently detected in active alcohol abusers (55/86, 64%) than in patients on sustained alcohol withdrawal longer than 6 months (1/8, 13%, p<0.005), HBV infection (2/8, 25%, P=0.03), non-alcohol related disease (9/29, 23%, p<0.0001) and in normal controls (3/22, 14%, p<0.0001); were more frequent in patients with cirrhosis than in those with steatosis (26/34, 76% vs 34/64, 53%, P=0.02); and were associated with elevated levels of ALT (anti-ADH β2, p<0.05), immunoglobulin A (p<0.05) and γ-glutamyl transpeptidase (P=0.01). Anti-ADH antibody positive serum samples were able to inhibit the enzymatic activity of ADH. These findings suggest that anti-ADH antibodies may be triggered by alcohol consumption and act as a disease activity marker in alcoholic liver disease.

Genetic variants in or near ADH1B and ADH1C affect susceptibility to alcohol dependence in a British and Irish population

Certain single nucleotide polymorphisms (SNPs) in genes encoding alcohol dehydrogenase (ADH) enzymes confer a significant protective effect against alcohol dependence syndrome (ADS) in East Asian populations. Recently, attention has focused on the role of these SNPs in determining ADS risk in European populations. To further elucidate these associations, SNPs of interest in ADH1B, ADH1C and the ADH1B/1C intergenic region were genotyped in a British and Irish population (ADS cases n = 1076: controls n = 1027) to assess their relative contribution to ADS risk. A highly significant, protective association was observed between the minor allele of rs1229984 in ADH1B and ADS risk [allelic P = 8.4 × 10(-6) , odds ratio (OR) = 0.26, 95 percent confidence interval, 0.14, 0.49]. Significant associations were also observed between ADS risk and the ADH1B/1C intergenic variant, rs1789891 [allelic P = 7.2 × 10(-5) , OR = 1.4 (1.2, 1.6)] and three non-synonymous SNPs rs698, rs1693482 and rs283413 in ADH1C. However, these associations were not completely independent; thus, while the ADH1B rs1229984 minor allele association was independent of those of the intergenic variant rs1789891 and the three ADH1C variants, the three ADH1C variants were not individually independent. In conclusion, the rare ADH1B rs1229984 mutation provides significant protection against ADS in this British and Irish population; other variants in the ADH gene cluster also alter ADS risk, although the strong linkage disequilibrium between SNPs at this location precluded clear identification of the variant(s) driving the associations.

Sex differences in mania phenotype and ethanol consumption in the lateral hypothalamic kindled rat model

Sex differences have been observed in mania phenotypes in humans. However the mechanisms underlying this difference are poorly understood. Activating the lateral hypothalamus is implicated in manic-like behaviors in rodents. Using newly established lateral hypothalamus kindled (LHK) rat mania model, we investigated sex differences of manic-like behaviors and its correlation with voluntary ethanol intake. We stimulated the lateral hypothalamus bilaterally in the male and female Wistar rats over five consecutive days. We recorded and quantified kindling-induced behaviors for each individual animal. We also assessed ethanol consumption using a two-bottle choice ethanol drinking as well as circadian locomotor activity counts daily throughout the experiment. We found notable sex differences in several aspects of manic-like behaviors during kindling. Males exhibited a significantly increased locomotor activity during the light phase, and reduced rest interval. On the other hand, females displayed significantly higher ethanol consumption and more frequent rearing behavior. However, no sex differences were present in the duration of sexual, feeding or grooming behaviors or in dark-phase activity counts. The excessive alcohol intake in LHK female rats is reminiscent of clinically reported sex differences in bipolar patients while the other phenotypic sex differences such as rearing and locomotor activity are less clearly described in clinical studies. Overall, our results lend further evidence for the validity of the LHK rat as a useful model to study brain region-specific molecular changes during mania and its correlation with alcohol use disorders.

Association and ancestry analysis of sequence variants in ADH and ALDH using alcohol-related phenotypes in a Native American community sample

Higher rates of alcohol use and other drug-dependence have been observed in some Native American (NA) populations relative to other ethnic groups in the US. Previous studies have shown that alcohol dehydrogenase (ADH) genes and aldehyde dehydrogenase (ALDH) genes may affect the risk of development of alcohol dependence, and that polymorphisms within these genes may differentially affect risk for the disorder depending on the ethnic group evaluated. We evaluated variations in the ADH and ALDH genes in a large study investigating risk factors for substance use in a NA population. We assessed ancestry admixture and tested for associations between alcohol-related phenotypes in the genomic regions around the ADH1-7 and ALDH2 and ALDH1A1 genes. Seventy-two ADH variants showed significant evidence of association with a severity level of alcohol drinking-related dependence symptoms phenotype. These significant variants spanned across the entire 7 ADH gene cluster regions. Two significant associations, one in ADH and one in ALDH2, were observed with alcohol dependence diagnosis. Seventeen variants showed significant association with the largest number of alcohol drinks ingested during any 24-hour period. Variants in or near ADH7 were significantly negatively associated with alcohol-related phenotypes, suggesting a potential protective effect of this gene. In addition, our results suggested that a higher degree of NA ancestry is associated with higher frequencies of potential risk variants and lower frequencies of potential protective variants for alcohol dependence phenotypes.

Assessment of a putative proton relay in Arabidopsis cinnamyl alcohol dehydrogenase catalysis

Extended proton relay systems have been proposed for various alcohol dehydrogenases, including the Arabidopsis thaliana cinnamyl alcohol dehydrogenases (AtCADs). Following a previous structural biology investigation of AtCAD5, the potential roles of three amino acid residues in a putative proton relay system, namely Thr49, His52 and Asp57, in AtCAD5, were investigated herein. Using site-directed mutagenesis, kinetic and isothermal titration calorimetry (ITC) analyses, it was established that the Thr49 residue was essential for overall catalytic conversion, whereas His52 and Asp57 residues were not. Mutation of the Thr49 residue to Ala resulted in near abolition of catalysis, with thermodynamic data indicating a negative enthalpic change (ΔH), as well as a significant decrease in binding affinity with NADPH, in contrast to wild type AtCAD5. Mutation of His52 and Asp57 residues by Ala did not significantly change either catalytic efficiency or thermodynamic parameters. Therefore, only the Thr49 residue is demonstrably essential for catalytic function. ITC analyses also suggested that for AtCAD5 catalysis, NADPH was bound first followed by p-coumaryl aldehyde.

Alcohol-metabolizing genes and alcohol phenotypes in an Israeli household sample

BACKGROUND

Alcohol dehydrogenase 1B and 1C (ADH1B and ADH1C) variants have been robustly associated with alcohol phenotypes in East Asian populations, but less so in non-Asian populations where prevalence of the most protective ADH1B allele is low (generally <5%). Further, the joint effects of ADH1B and ADH1C on alcohol phenotypes have been unclear. Therefore, we tested the independent and joint effects of ADH1B and ADH1C on alcohol phenotypes in an Israeli sample, with higher prevalence of the most protective ADH1B allele than other non-Asian populations.

METHODS

A structured interview assessed lifetime drinking and alcohol use disorders (AUDs) in adult Israeli household residents. Four single nucleotide polymorphisms (SNPs) were genotyped: ADH1B (rs1229984, rs1229982, and rs1159918) and ADH1C (rs698). Regression analysis examined the association between alcohol phenotypes and each SNP (absence vs. presence of the protective allele) as well as rs698/rs1229984 diplotypes (also indicating absence or presence of protective alleles) in lifetime drinkers (n = 1,129).

RESULTS

Lack of the ADH1B rs1229984 protective allele was significantly associated with consumption- and AUD-related phenotypes (OR = 1.77 for AUD; OR = 1.83 for risk drinking), while lack of the ADH1C rs698 protective allele was significantly associated with AUD-related phenotypes (OR = 2.32 for AUD). Diplotype analysis indicated that jointly ADH1B and ADH1C significantly influenced AUD-related phenotypes. For example, among those without protective alleles for ADH1B or ADH1C, OR for AUD was 1.87 as compared to those without the protective allele for ADH1B only and was 3.16 as compared to those with protective alleles for both ADH1B and ADH1C.

CONCLUSIONS

This study adds support for the relationship of ADH1B and ADH1C and alcohol phenotypes in non-Asians. Further, these findings help clarify the mixed results from previous studies by showing that ADH1B and ADH1C jointly effect AUDs, but not consumption. Studies of the association between alcohol phenotypes and either ADH1B or ADH1C alone may employ an oversimplified model, masking relevant information.

Bradykinetic alcohol dehydrogenases make yeast fitter for growth in the presence of allyl alcohol

Previous studies showed that fitter yeast (Saccharomyces cerevisiae) that can grow by fermenting glucose in the presence of allyl alcohol, which is oxidized by alcohol dehydrogenase I (ADH1) to toxic acrolein, had mutations in the ADH1 gene that led to decreased ADH activity. These yeast may grow more slowly due to slower reduction of acetaldehyde and a higher NADH/NAD(+) ratio, which should decrease the oxidation of allyl alcohol. We determined steady-state kinetic constants for three yeast ADHs with new site-directed substitutions and examined the correlation between catalytic efficiency and growth on selective media of yeast expressing six different ADHs. The H15R substitution (a test for electrostatic effects) is on the surface of ADH and has small effects on the kinetics. The H44R substitution (affecting interactions with the coenzyme pyrophosphate) was previously shown to decrease affinity for coenzymes 2-4-fold and turnover numbers (V/Et) by 4-6-fold. The W82R substitution is distant from the active site, but decreases turnover numbers by 5-6-fold, perhaps by effects on protein dynamics. The E67Q substitution near the catalytic zinc was shown previously to increase the Michaelis constant for acetaldehyde and to decrease turnover for ethanol oxidation. The W54R substitution, in the substrate binding site, increases kinetic constants (Ks, by >10-fold) while decreasing turnover numbers by 2-7-fold. Growth of yeast expressing the different ADHs on YPD plates (yeast extract, peptone and dextrose) plus antimycin to require fermentation, was positively correlated with the log of catalytic efficiency for the sequential bi reaction (V1/KiaKb=KeqV2/KpKiq, varying over 4 orders of magnitude, adjusted for different levels of ADH expression) in the order: WT≈H15R>H44R>W82R>E67Q>W54R. Growth on YPD plus 10mM allyl alcohol was inversely correlated with catalytic efficiency. The fitter yeast are "bradytrophs" (slow growing) because the ADHs have decreased catalytic efficiency.

Reduction of ethanol consumption in alcohol-preferring rats by dual expression gene transfer

AIMS

To mimic, in an animal model of alcoholism, the protective phenotype against alcohol consumption observed in humans carrying a fast alcohol dehydrogenase (ADH1B*2) and an inactive aldehyde dehydrogenase (ALDH2*2).

METHODS

We developed a multiple expression cassette adenoviral vector (AdV-ADH/asALDH2) encoding both a fast rat ADH and an antisense RNA against rat ALDH2. A control adenoviral vector (AdV-C) containing intronic non-coding DNA was also developed. These adenoviral vectors were administered intravenously to rats bred as high alcohol-drinkers (University of Chile bibulous) that were previously rendered alcohol dependent by a 75-day period of voluntary 10% ethanol intake.

RESULTS

Animals administered AdV-ADH/asALDH2 showed a 176% increase in liver ADH activity, whereas liver ALDH2 activity was reduced by 24%, and upon the administration of a dose of ethanol (1 g/kg, i.p.), these showed arterial acetaldehyde levels that were 400% higher than those of animals administered AdV-C. Rats that received the AdV-ADH/asALDH2 vector reduced by 60% their voluntary ethanol intake versus controls.

CONCLUSION

This study provides evidence that the simultaneous increase of liver ADH and a reduction of ALDH activity by gene transfer could constitute a potential therapeutic strategy for the treatment of alcoholism.

Association of alcohol dehydrogenase genes with alcohol-related phenotypes in a Native American community sample

BACKGROUND

Previous linkage studies, including a study of the Native American population described in the present report, have provided evidence for linkage of alcohol dependence and related traits to chromosome 4q near a cluster of alcohol dehydrogenase (ADH) genes, which encode enzymes of alcohol metabolism.

METHODS

The present study tested for associations between alcohol dependence and related traits and 22 single-nucleotide polymorphisms (SNPs) spanning the 7 ADH genes. Participants included 586 adult men and women recruited from 8 contiguous Native American reservations. A structured interview was used to assess DSM-III-R alcohol dependence criteria as well as a set of severe alcohol misuse symptoms and alcohol withdrawal symptoms.

RESULTS

No evidence for association with the alcohol dependence diagnosis was observed, but an SNP in exon 9 of ADH1B (rs2066702; ADH1B*3) and an SNP at the 5' end of ADH4 (rs3762894) showed significant evidence of association with the presence of withdrawal symptoms (p = 0.0018 and 0.0012, respectively). Further, a haplotype analysis of these 2 SNPs suggested that the haplotypes containing either of the minor alleles were protective against alcohol withdrawal relative to the ancestral haplotype (p = 0.000006).

CONCLUSIONS

These results suggest that variants in the ADH1B and ADH4 genes may be protective against the development of some symptoms associated with alcohol dependence.

Shortened telomeres in individuals with abuse in alcohol consumption

Alcohol abuse leads to earlier onset of aging-related diseases, including cancer at multiple sites. Shorter telomere length (TL) in peripheral blood leucocytes (PBLs), a marker of biological aging, has been associated with alcohol-related cancer risks. Whether alcohol abusers exhibit accelerated biological aging, as reflected in PBL-TL, has never been examined. To investigated the effect of alcohol abuse on PBL-TL and its interaction with alcohol metabolic genotypes, we examined 200 drunk-driving traffic offenders diagnosed as alcohol abusers as per the Diagnostic and Statistical Manual of Mental Disorders [DSM-IV-TR] and enrolled in a probation program, and 257 social drinkers (controls). We assessed alcohol intake using self-reported drink-units/day and conventional alcohol abuse biomarkers (serum γ-glutamyltrasferase [GGT] and mean corpuscular volume of erythrocytes [MCV]). We used multivariable models to compute TL geometric means (GM) adjusted for age, smoking, BMI, diet, job at elevated risk of accident, genotoxic exposures. TL was nearly halved in alcohol abusers compared with controls (GMs 0.42 vs. 0.87 relative T/S ratio; p<0.0001) and decreased in relation with increasing drink-units/day (p-trend=0.003). Individuals drinking >4 drink-units/day had substantially shorter TL than those drinking ≤4 drink-units/day (GMs 0.48 vs. 0.61 T/S, p=0.002). Carriers of the common ADH1B*1/*1 (rs1229984) genotype were more likely to be abusers (p=0.008), reported higher drink-units/day (p=0.0003), and exhibited shorter TL (p<0.0001). The rs698 ADH1C and rs671 ALDH2 polymorphisms were not associated with TL. The decrease in PBL-TL modulated by the alcohol metabolic genotype ADH1B*1/*1 may represent a novel mechanism potentially related to alcohol carcinogenesis in alcohol abusers.

Origins of the high catalytic activity of human alcohol dehydrogenase 4 studied with horse liver A317C alcohol dehydrogenase

The turnover numbers and other kinetic constants for human alcohol dehydrogenase (ADH) 4 ("stomach" isoenzyme) are substantially larger (10-100-fold) than those for human class I and horse liver alcohol dehydrogenases. Comparison of the primary amino acid sequences (69% identity) and tertiary structures of these enzymes led to the suggestion that residue 317, which makes a hydrogen bond with the nicotinamide amide nitrogen of the coenzyme, may account for these differences. Ala-317 in the class I enzymes is substituted with Cys in human ADH4, and locally different conformations of the peptide backbones could affect coenzyme binding. This hypothesis was tested by making the A317C substitution in horse liver ADH1E and comparisons to the wild-type ADH1E. The steady-state kinetic constants for the oxidation of benzyl alcohol and the reduction of benzaldehyde catalyzed by the A317C enzyme were very similar (up to about 2-fold differences) to those for the wild-type enzyme. Transient kinetics showed that the rate constants for binding of NAD(+) and NADH were also similar. Transient reaction data were fitted to the full Ordered Bi Bi mechanism and showed that the rate constants for hydride transfer decreased by about 2.8-fold with the A317C substitution. The structure of A317C ADH1E complexed with NAD(+) and 2,3,4,5,6-pentafluorobenzyl alcohol at 1.2 Å resolution is essentially identical to the structure of the wild-type enzyme, except near residue 317 where the additional sulfhydryl group displaces a water molecule that is present in the wild-type enzyme. ADH is adaptable and can tolerate internal substitutions, but the protein dynamics apparently are affected, as reflected in rates of hydride transfer. The A317C substitution is not solely responsible for the larger kinetic constants in human ADH4; thus, the differences in catalytic activity must arise from one or more of the other hundred substitutions in the enzyme.

Mechanism of protection against alcoholism by an alcohol dehydrogenase polymorphism: development of an animal model

Humans who carry a point mutation in the gene coding for alcohol dehydrogenase-1B (ADH1B*2; Arg47His) are markedly protected against alcoholism. Although this mutation results in a 100-fold increase in enzyme activity, it has not been reported to cause higher levels of acetaldehyde, a metabolite of ethanol known to deter alcohol intake. Hence, the mechanism by which this mutation confers protection against alcoholism is unknown. To study this protective effect, the wild-type rat cDNA encoding rADH-47Arg was mutated to encode rADH-47His, mimicking the human mutation. The mutated cDNA was incorporated into an adenoviral vector and administered to genetically selected alcohol-preferring rats. The V(max) of rADH-47His was 6-fold higher (P<0.001) than that of the wild-type rADH-47Arg. Animals transduced with rAdh-47His showed a 90% (P<0.01) increase in liver ADH activity and a 50% reduction (P<0.001) in voluntary ethanol intake. In animals transduced with rAdh-47His, administration of ethanol (1g/kg) produced a short-lived increase of arterial blood acetaldehyde concentration to levels that were 3.5- to 5-fold greater than those in animals transduced with the wild-type rAdh-47Arg vector or with a noncoding vector. This brief increase (burst) in arterial acetaldehyde concentration after ethanol ingestion may constitute the mechanism by which humans carrying the ADH1B*2 allele are protected against alcoholism.

Pharmacokinetics of carisbamate (RWJ-333369) in healthy Japanese and Western subjects

PURPOSE

To compare the pharmacokinetics of carisbamate (RWJ-333369) in healthy Japanese and Western adults, and to comparatively assess carisbamate safety and tolerability between the two populations.

METHODS

An open-label study was conducted in 24 Japanese and 24 Caucasian healthy subjects. Subjects received a single oral dose of 250 mg carisbamate on day 1 followed by a 3-day washout period; twice-daily dosing of 250 mg carisbamate on days 5-8; subsequently, 500 mg on days 9-12 and a single dose of 500 mg on day 13. Plasma samples were collected for a pharmacokinetic analysis on days 1, 8, and 13. Plasma and urine samples were analyzed for carisbamate and its urinary metabolites by liquid-chromatography-mass-spectrometry.

RESULTS

Following a single dose, carisbamate Cmax and area under the curve (AUC) geometric mean ratios were 16.4% and 28.8% higher in Japanese than in Caucasians, respectively; these differences were statistically significant and their 90% confidence intervals (CIs) fell outside of the 80-125% limits, which are considered not to be of clinical significance. With dose-body weight normalization, Cmax and AUC were similar in Japanese and Caucasian subjects and the 90% CIs were within the 80-125% boundaries. Carisbamate was well tolerated, and its mean oral clearance and half-life were similar in both groups, ranging from 35.1-41.4 ml/h/kg and 11.5-12.8 h.

DISCUSSION

Carisbamate plasma exposure (AUC) and C(max) in Japanese subjects is approximately 20-25% higher than in Caucasians due to a higher mg/kg dose. After body weight normalization, carisbamate pharmacokinetics was similar between Japanese and Caucasian subjects following single and multiple dosing, and showed the same dose proportionality.

Gene identification and characterization of 5-formyl-3-hydroxy-2-methylpyridine 4-carboxylic acid 5-dehydrogenase, an NAD+-dependent dismutase

A chromosomal gene, mlr6793, in Mesorhizobium loti was identified as the gene encoding 5-formyl-3-hydroxy-2-methylpyridine 4-carboxylic acid (FHMPC) dehydrogenase (dismutase) involved in the degradation pathway for pyridoxine (vitamin B(6)). The homogenously purified recombinant enzyme has a molecular mass of 59.1 kDa and is a homodimeric protein. FHMPC dehydrogenase catalyses practically irreversible oxidation (k(cat) = 204 s(-1)) of FHMPC (K(m) = 48.2 microM) by NAD(+) (K(m) = 34.3 microM) to 3-hydroxy-2-methyl-pyridine 4, 5-dicarboxylic acid (HMPDC), and practically irreversible reduction (k(cat) = 217 s(-1)) of FHMPC (K(m) = 24.9 microM) by NADH (K(m) = 12.4 microM) to 4-pyridoxic acid. When the enzyme reaction was started with the combination of FHMPC and NAD(+) or that of FHMPC and NADH, HMPDC and 4-pyridoxic acid were produced in an almost equimolar ratio throughout the reaction. FHMPC dehydrogenase belongs to the 3-hydroxyacyl-CoA dehydrogenase family with 31% identity with the human enzyme: it has probable catalytic diad residues, i.e. His137 and Glu149. The H137L mutant enzyme showed no measurable activity. The E149Q one was stable in contrast to the corresponding human 3-hydroxyacyl-CoA dehydrogenase mutant, and showed unique pH optima depending on the co-substrates used for the reaction.

Alcohol dehydrogenase genetic polymorphisms, low-to-moderate alcohol consumption, and risk of breast cancer

BACKGROUND

In vitro, human isoenzymes encoded by genes homozygous for the ADH1C*1 or ADH1B*2 alleles metabolize ethanol to acetaldehyde at a faster rate than those homozygous for the ADH1C*2 or ADH1B*1 allele. Because alcohol is a known risk factor for breast cancer, we evaluated the joint association of genetic variants in ADH and alcohol consumption in relation to breast cancer.

METHODS

A nested case-control study of 321 cases and matched controls was conducted. Five single nucleotide polymorphisms (SNPs) in the ADH1C and ADH1B genes were genotyped. Logistic regression was used to assess odds ratios (ORs) and 95% confidence limits (CIs) for each SNP. Haplotype analysis of all 5 SNPs was also undertaken.

RESULTS

Among drinkers, the median intake of total alcohol was 13 g/wk (10th-90th percentiles; 4.5-135.9) in cases and 18 g/wk (10th-90th percentiles; 4.5-104.1) in controls. Women who drank alcohol tended to be at an increased risk of developing breast cancer compared with those who did not drink (OR=1.40%, 95% CI 0.97-2.03), particularly those who were premenopausal at the time of breast cancer diagnosis (OR=2.69%, 95% CI: 1.00-7.26). Of the known functional alleles, breast cancer risk was not significantly increased among carriers of at least 1 ADH1C*1 or ADH1B*2 allele, when compared with those homozygous for the genotype at each locus. However, breast cancer risk tended to be lower among women who inherited the G allele at ADH1B IVS1+896A>G (OR=0.62, 95% CI 0.37-1.04). Overall haplotype frequencies were not significantly different between cases and controls.

CONCLUSIONS

In this study low levels of alcohol are associated with a modest increase in breast cancer risk that is not altered by known functional allelic variants of the ADH1B and 1C gene. The protective association conferred by the G allele at ADH1B IVS1+896A>G needs further evaluation.

Apo and Holo structures of an NADPH-dependent cinnamyl alcohol dehydrogenase from Saccharomyces cerevisiae

The crystal structure of Saccharomyces cerevisiae ScAdh6p has been solved using the anomalous signal from the two zinc atoms found per subunit, and it constitutes the first structure determined from a member of the cinnamyl alcohol dehydrogenase family. ScAdh6p subunits exhibit the general fold of the medium-chain dehydrogenases/reductases (MDR) but with distinct specific characteristics. In the three crystal structures solved (two trigonal and one monoclinic), ScAdh6p molecules appear to be structural heterodimers composed of one subunit in the apo and the second subunit in the holo conformation. Between the two conformations, the relative disposition of domains remains unchanged, while two loops, Cys250-Asn260 and Ile277-Lys292, experience large movements. The apo-apo structure is disfavoured because of steric impairment involving the loop Ile277-Lys292, while in the holo-holo conformation some of the hydrogen bonds between subunits would break apart. These suggest that the first NADPH molecule would bind to the enzyme much more tightly than the second. In addition, fluorimetric analysis of NADPH binding demonstrates that only one cofactor molecule binds per dimer. Therefore, ScAdh6p appears to function according to a half-of-the-sites reactivity mechanism, resulting from a pre-existing (prior to cofactor binding) tendency for the structural asymmetry in the dimer. The specificity of ScAdh6p towards NADPH is mainly due to the tripod-like interactions of the terminal phosphate group with Ser210, Arg211 and Lys215. The size and the shape of the substrate-binding pocket correlate well with the substrate specificity of ScAdh6p towards cinnamaldehyde and other aromatic compounds. The structural relationships of ScAdh6p with other MDR structures are analysed.

The metabolic activation of abacavir by human liver cytosol and expressed human alcohol dehydrogenase isozymes

Abacavir (ZIAGEN) is a reverse transcriptase inhibitor marketed for the treatment of HIV-1 infection. A small percentage of patients experience a hypersensitivity reaction indicating immune system involvement and bioactivation. A major route of metabolism for abacavir is oxidation of a primary betagamma unsaturated alcohol to a carboxylic acid via an aldehyde intermediate. This process was shown to be mediated in vitro by human cytosol and NAD, and subsequently the alphaalpha and gamma2gamma2 human isoforms of alcohol dehydrogenase (ADH). The alphaalpha isoform effected two sequential oxidation steps to form the acid metabolite and two isomers, qualitatively reflective of in vitro cytosolic profiles. The gamma2gamma2 isozyme generated primarily an isomer of abacavir, which was minor in the alphaalpha profiles. The aldehyde intermediate could be trapped in incubations with both isozymes as an oxime derivative. These metabolites can be rationalized as arising via the aldehyde which undergoes isomerization and further oxidation by the alphaalpha enzyme or reduction by the gamma2gamma2 isozyme. Non-extractable abacavir protein residues were generated in cytosol, and with alphaalpha and gamma2gamma2 incubations in the presence of human serum albumin (HSA). Metabolism and residue formation were blocked by the ADH inhibitor 4-methyl pyrazole (4-MP). The residues generated by the alphaalpha and gamma2gamma2 incubations were analyzed by SDS-PAGE with immunochemical detection. The binding of rabbit anti-abacavir antibody to abacavir-HSA was shown to be dependent on metabolism (i.e. NAD-dependent and 4-MP sensitive). The mechanism of covalent binding remains to be established, but significantly less abacavir-protein residue was detected with an analog of abacavir in which the double bond was removed, suggestive of a double bond migration and 1,4 addition process.

Kinetic mechanism of human class IV alcohol dehydrogenase functioning as retinol dehydrogenase

Molecular genetic studies have indicated that alcohol dehydrogenase may be involved in the synthesis of retinoic acid, a hormonal molecule regulating diverse cellular functions at the transcriptional level. Class IV alcohol dehydrogenase (ADH) has been reported to be the most efficient enzyme catalyzing oxidation of retinol in human ADH family. Initial velocity, product inhibition, and dead-end inhibition experiments were performed with the recombinant human class IV ADH to elucidate kinetic mechanism with all-trans-retinol and all-trans-retinal as natural substrates. Fluorescence quenching was titrated in formation of the binary and abortive ternary enzyme complexes. The minimal mechanism deduced from steady-state kinetic and equilibrium binding studies is best described as an asymmetric rapid equilibrium random mechanism with two dead-end ternary complexes for retinol oxidation and a rapid equilibrium ordered mechanism with one dead-end ternary complex for retinal reduction, a unique mechanistic form for zinc-containing ADHs in the medium chain dehydrogenase/reductase superfamily. Dissociation constants for the binary complexes as well as the productive and abortive ternary complexes determined from different experimental approaches are in reasonable agreement. Kinetic isotope effect studies suggest rate-limiting isomerization of the central ternary complexes in both reaction directions. The potential interference of retinol metabolism by ethanol through the ADH pathway may play a significant role in the pathogenesis of fetal alcohol syndrome and alcohol-related upper digestive tract cancer.

A review of alcohol clearance in humans

The level of blood or brain alcohol is considered to influence alcohol ingestion by causing subjective perceptions or neural activations that are reinforcing or rewarding. Alcohol-dependent people may try to maintain some desired tissue level, drinking to replace the millimolar levels that were cleared from the blood by metabolism. The biomedical literature describes many approaches to understanding the role of blood alcohol levels in human physiology and behavior, and this review examines some of the published results. They include the general kinetics of intake and removal of beverage alcohol as well as the characteristics of many different catalysts that can interact with alcohol. Because ingested alcohol creates blood levels that are a 1000-fold greater than those normally experienced during abstinence, ethanol may impose itself as an alternate substrate for the many oxidoreductases that act physiologically on other endogenous alcohols. Many enzymes that can act on millimolar ethanol have been isolated, and their structural genes are sequenced. Unfortunately, the genetic sequence does not indicate the physiological material upon which the translated gene product may act. In a sense, the set of enzymes with catalytic sites occupied by millimolar ethanol during alcohol drinking might constructively be regarded as "orphan gene products" whose physiological role remains to be clarified. This review is designed to indicate some of what is known, what is not known, and what needs to be known to improve the interpretations regarding adaptations to beverage alcohol and the ability of millimolar levels of alcohol to diminish dysphoria. The dysphoria may be influenced by ethanol, by ethanol metabolites, or by altered metabolism of currently unspecified endogenous substrates. A major challenge is to evaluate the multiple alternative variables within a context that stimulates curiosity and encourages quantitative tests of the relative contribution of each variable to the overall physiology of an individual.

cDNA sequence and catalytic properties of a chick embryo alcohol dehydrogenase that oxidizes retinol and 3beta,5alpha-hydroxysteroids

This study was undertaken to identify the cytosolic 40-kDa zinc-containing alcohol dehydrogenases that oxidize all-trans-retinol and steroid alcohols in fetal tissues. Degenerate oligonucleotide primers were used to amplify by polymerase chain reaction 500-base pair fragments of alcohol dehydrogenase cDNAs from chick embryo limb buds and heart. cDNA fragments that encode an unknown putative alcohol dehydrogenase as well as the class III alcohol dehydrogenase were identified. The new cDNA hybridized with two messages of approximately 2 and 3 kilobase pairs in the adult chicken liver but not in the adult heart, muscle, testis, or brain. The corresponding complete cDNA clones with a total length of 1390 base pairs were isolated from a chicken liver lambdagt11 cDNA library. The open reading frame encoded a 375-amino acid polypeptide that exhibited 67 and 68% sequence identity with chicken class I and III alcohol dehydrogenases, respectively, and had lower identity with mammalian class II (55-58%) and IV (62%) isozymes. Expression of the new cDNA in Escherichia coli yielded an active alcohol dehydrogenase (ADH-F) with subunit molecular mass of approximately 40 kDa. The specific activity of the recombinant enzyme, calculated from active site titration of NADH binding, was 3.4 min-1 for ethanol at pH 7.4 and 25 degrees C. ADH-F was stereospecific for the 3beta,5alpha- versus 3beta,5beta-hydroxysteroids. The Km value for ethanol at pH 7.4 was 17 mM compared with 56 microM for all-trans-retinol and 31 microM for epiandrosterone. Antiserum against ADH-F recognized corresponding protein in the chicken liver homogenate. We suggest that ADH-F represents a new class of alcohol dehydrogenase, class VII, based on its primary structure and catalytic properties.

X-ray structure of human beta3beta3 alcohol dehydrogenase. The contribution of ionic interactions to coenzyme binding

The three-dimensional structure of the human beta3beta3 dimeric alcohol dehydrogenase (beta3) was determined to 2.4-A resolution. beta3 was crystallized as a ternary complex with the coenzyme NAD+ and the competitive inhibitor 4-iodopyrazole. beta3 is a polymorphic variant at ADH2 that differs from beta1 by a single amino acid substitution of Arg-369 --> Cys. The available x-ray structures of mammalian alcohol dehydrogenases show that the side chain of Arg-369 forms an ion pair with the NAD(H) pyrophosphate to stabilize the E.NAD(H) complex. The Cys-369 side chain of beta3 cannot form this interaction. The three-dimensional structures of beta3 and beta1 are virtually identical, with the exception that Cys-369 and two water molecules in beta3 occupy the position of Arg-369 in beta1. The two waters occupy the same positions as two guanidino nitrogens of Arg-369. Hence, the number of hydrogen bonding interactions between the enzyme and NAD(H) are the same for both isoenzymes. However, beta3 differs from beta1 by the loss of the electrostatic interaction between the NAD(H) pyrophosphate and the Arg-369 side chain. The equilibrium dissociation constants of beta3 for NAD+ and NADH are 350-fold and 4000-fold higher, respectively, than those for beta1. These changes correspond to binding free energy differences of 3.5 kcal/mol for NAD+ and 4.9 kcal/mol for NADH. Thus, the Arg-369 --> Cys substitution of beta3 isoenzyme destabilizes the interaction between coenzyme and beta3 alcohol dehydrogenase.

Cloning and characterization of a novel rat alcohol dehydrogenase of class II type

A class II type alcohol dehydrogenase from rat liver was characterized at the cDNA level after screening cDNA libraries in combination with PCR amplification of the 5'-part. The open reading frame translates into a polypeptide of 376 amino acid residues, which show 73% positional identity to the human class II enzyme. This suggests that the class II enzyme is the most variable form of the mammalian alcohol dehydrogenases. A deletion is apparent corresponding to position 294 of the human enzyme and amino acid residues unique to the rat protein of those interacting with the coenzyme NAD+ are found at positions 47, 51, 178, and 271. Position 47 is occupied by Pro instead of Arg or His found in most mammalian alcohol dehydrogenases. This exchanged residue will not hydrogen bond to the pyrophosphate of the coenzyme and will change the local environment around position 47 to strictly hydrophobic.

Cimetidine inhibition of human gastric and liver alcohol dehydrogenase isoenzymes: identification of inhibitor complexes by kinetics and molecular modeling

Cimetidine, an H2-receptor antagonist, is one of the most commonly prescribed drugs in the world. It has been reported to increase blood alcohol concentrations in drinking individuals. To determine if this increase could be due to inhibition of alcohol dehydrogenase activity, the effect of the drug on ethanol oxidation by gastric sigma sigma alcohol dehydrogenase and liver beta 2 beta 2, pi pi, and chi chi alcohol dehydrogenase isoenzymes was observed. Cimetidine inhibited all isoenzymes studied except chi chi; the chi chi isoenzyme showed no inhibition up to 5 mM cimetidine. Inhibition of the alcohol dehydrogenase isoenzymes by the H2-receptor antagonists nizatidine, ranitidine, and famotidine was negligible. Docking simulations with the beta 2.NAD+.4-iodopyrazole X-ray structure indicated that cimetidine fit well into the substrate binding site. The substitution on the thiazole ring of nizatidine, however, prevented docking into the binding site. Cimetidine inhibition of ethanol oxidation by sigma sigma and beta 2 beta 2 was competitive with varied ethanol, exhibiting Ki values of 2.8 +/- 0.4 mM and 0.77 +/- 0.07 mM, respectively. Cimetidine inhibition of ethanol oxidation by pi pi was noncompetitive with varied ethanol (Ki = 0.50 +/- 0.03 mM). Inhibition of ethanol oxidation by sigma sigma and beta 2 beta 2 with varied NAD+ was competitive. These results, together with the cimetidine inhibition kinetics of acetaldehyde reduction by sigma sigma and beta 2 beta 2, with either varied NADH or varied acetaldehyde, are consistent with cimetidine binding to two enzyme species. These species are free enzyme and the productive enzyme.NAD+ complex.

Alcohol dehydrogenase of class IV (sigma sigma-ADH) from human stomach. cDNA sequence and structure/function relationships

Human stomach mucosa contains a characteristic alcohol dehydrogenase (ADH) enzyme, sigma sigma-ADH. Its cDNA has been cloned from a human stomach library and sequenced. The deduced amino acid sequence shows 59-70% identities with the other human ADH classes, demonstrating that the stomach enzyme represents a distinct structure, constituting class IV, coded by a separate gene, ADH7. The amino acid identity with the rat stomach class IV ADH is 88%, which is intermediate between constant and variable dehydrogenases. This value reflects higher conservation than for the classical liver enzymes of class I, compatible with a separate functional significance of the class IV enzyme. Its enzymic features can be correlated with its structural characteristics. The residues lining the substrate-binding cleft are bulky and hydrophobic, similar to those of the class I enzyme; this explains the similar specificity of both classes, compatible with the origin of class IV from class I. Position 47 has Arg, in contrast to Gly in the rat class IV enzyme, but this Arg is still associated with an extremely high activity (kcat = 1510 min-1) and weak coenzyme binding (KiaNAD+ = 1.6 mM). Thus, the strong interaction with coenzyme imposed by Arg47 in class I is probably compensated for in class IV by changes that may negatively affect coenzyme binding: Glu230, His271, Asn260, Asn261, Asn363. The still higher activity and weaker coenzyme binding of rat class IV (kcat = 2600 min-1, KiaNAD = 4 mM) can be correlated to the exchanges to Gly47, Gln230 and Tyr363. An important change at position 294, with Val in human and Ala in rat class IV, is probably responsible for the dramatic difference in Km values for ethanol between human (37 mM) and rat (2.4 M) class IV enzymes.

Catalytic efficiency of human alcohol dehydrogenases for retinol oxidation and retinal reduction

Mammalian alcohol dehydrogenase (ADH) is thought to be involved in the reversible oxidation of vitamin A or retinol to retinal for retinoic acid synthesis. Retinoic acid is a potent transcriptional regulator and a morphogen. It was proposed that the competition of consumed ethanol with retinol oxidation by ADH might explain developmental disorders seen with fetal alcohol syndrome. We report herein the relative efficiency (V/Km) of eight human ADH isoenzymes for oxidation of all-trans-retinol and reduction of three retinal isomers (all-trans, 9-cis, and 13-cis-retinal). Class IV sigma sigma and class II pi pi isoenzymes are the most efficient forms, with V/Km values approximately 100 and 30 times greater, respectively, than class I beta 1 beta 1 or gamma 1 gamma 1, sigma sigma exhibits the highest V/Km (1-2 microns-1min-1), followed by pi pi, with V/Km of 0.5-0.6 microns-1min-1 for all-trans-retinol, all-trans-retinal, and 9-cis-retinal. pi pi also has the lowest Km (11-14 microns) for all-trans-retinol and three retinal isomers. alpha alpha shows an intermediate efficiency, with V/Km of 0.09-0.2 microns-1min-1 and a relatively low Km of 16-24 microns for all four substrates. alpha alpha has the highest efficiency of all tested isoenzymes for 13-cis-retinal. Class III chi chi is inactive with all the tested retinoids.(ABSTRACT TRUNCATED AT 250 WORDS)

Site-directed mutagenesis and enzyme properties of mammalian alcohol dehydrogenases correlated with their tissue distribution

Site-directed mutagenesis of mammalian alcohol dehydrogenases has helped to explain functional differences between enzymes within the protein family and traced these characteristics to specific amino acid residues. A threonine/serine exchange at position 48 in the human beta/gamma subunits can explain sensitivity to testosterone inhibition, as well as steroid dehydrogenase activity. It is possible to correlate the glutathione-dependent formaldehyde dehydrogenase activity of class III alcohol dehydrogenase with an arginine at position 115. Tissue distribution analysis of the three initially established classes of mammalian alcohol dehydrogenase show pronouncedly different patterns. Class I alcohol dehydrogenase is widespread but varies between the tissues, and exists in small amounts in the brain. The occurrence of class II is limited in contrast to the class III enzyme which is abundant in all tissues examined. The latter probably reflects the need for scavenging of formaldehyde in cytoprotection. Additional enzyme forms of mammalian alcohol dehydrogenase have been detected and have to be investigated further, together with the enzymes characterized earlier, regarding their physiological role in alcohol metabolism.

Tryptophan fluorescence quenching by alkaline pH and ternary complex formation in human beta 1 beta 1 and horse EE alcohol dehydrogenases

The horse EE and human beta 1 beta 1 alcohol dehydrogenase isoenzymes have almost identical protein backbone folding patterns and contain 2 tryptophans per subunit (Trp-15 and Trp-314). Tyr-286, which had been proposed to quench the fluorescence of Trp-314 by resonance energy transfer at alkaline pH in EE, is substituted by Cys in beta 1 beta 1. The proposed role of Tyr-286 in pH-dependent quenching of EE is confirmed by our observation that tryptophan fluorescence of beta 1 beta 1 is not substantially quenched at alkaline pH. Tyr-286 had also been implicated in the quenching of Trp-314 upon formation of the EE-NAD(+)-trifluoroethanol ternary complex. However, beta 1 beta 1 exhibits the same extent of tryptophan fluorescence quenching as EE upon complexation, which strongly suggests that Tyr-286 is not involved in ternary complex quenching.

Human alcohol dehydrogenase: dependence of secondary alcohol oxidation on the amino acids at positions 93 and 94

The human liver alpha alpha and beta 1 beta 1 isoenzymes are straight-chain alcohol dehydrogenases with different efficiencies toward secondary alcohols. Two of the 24 amino acid substitutions in alpha alpha (A for F93 and I for T94) were made by site-directed mutagenesis of beta 1 beta 1 and the substrate specificity of beta 93A94I was examined. The Vmax/KM values of beta 93A94I for secondary alcohols (especially R enantiomers) are similar to that of alpha alpha and as much as 4000-fold greater than beta 1 beta 1, but the dependences of Vmax/KM on primary alcohol chain length are similar to beta 1 beta 1, but not alpha alpha. Thus, the substitutions of A for F93 and I for T94 in beta 1 beta 1 account for the increased efficiency towards secondary alcohols and stereoselectivity for enantiomeric alcohols, but not for the effects of chain length on the Vmax/KM for primary alcohols seen with alpha alpha.