Avian alcohol dehydrogenase: the chicken liver enzyme. Primary structure, cDNA-cloning, and relationships to other alcohol dehydrogenases

Quercetin attenuates lipopolysaccharide-induced hepatic inflammation by modulating autophagy and necroptosis

Lipopolysaccharide (LPS) from Gram-negative bacteria initially induces liver inflammation with proinflammatory cytokines expressions. However, the underlying hepatoprotective mechanism of quercetin on LPS-induced hepatic inflammation remains unclear. Specific pathogen-free chicken embryos (n = 120) were allocated control vehicle, PBS with or without ethanol vehicle, LPS (125 ng/egg) with or without quercetin treatment (10, 20, or 40 nmol/egg, respectively), quercetin groups (10, 20, or 40 nmol/egg). Fifteen-day-old embryonated eggs were inoculated abovementioned solutions via the allantoic cavity. At embryonic d 19, the livers of the embryos were collected for histopathological examination, RNA extraction, real-time polymerase chain reaction, and immunohistochemistry investigation. We found that the liver presented inflammatory response (heterophils infiltration) after LPS induction. The LPS-induced mRNA expressions of inflammation-related factors (TLR4, TNFα, IL-1β, IL-10, IL-6, MYD88, NF-κB1, p38, and MMP3) were upregulated after LPS induction when compared with the PBS group, while quercetin could downregulate these expressions as compared with the LPS group. Quercetin significantly decreased the immunopositivity to TLR4 and MMP3 in the treatment group when compared with the LPS group. Quercetin could significantly downregulate the mRNA expressions of autophagy-related genes (ATG5, ATG7, Beclin-1, LC3A, and LC3B) and necroptosis-related genes (Fas, Bcl-2, Drp1, and RIPK1) after LPS induction. Quercetin significantly decreased the immunopositivity to LC3 in the treatment group when compared with the LPS group; meanwhile, quercetin significantly decreased the protein expressions of LC3-I, LC3-II, and the rate of LC3-II/LC3-I. In conclusions, quercetin can alleviate hepatic inflammation induced by LPS through modulating autophagy and necroptosis.

Quercetin Alleviates Inflammation and Energy Deficiency Induced by Lipopolysaccharide in Chicken Embryos

Energy deficiency causes multiple organ dysfunctions after LPS induction. Quercetin is a phenolic compound found in herbal medicines. However, the effects of quercetin in alleviating LPS-induced energy deficiency remain unclear. In the present study, an in vivo LPS-induced inflammation model was established in chicken embryos. Specific pathogen-free chicken embryos (n = 120) were allocated to control, PBS with or without ethanol, quercetin (10, 20, or 40 nmol, respectively), and LPS (125 ng/egg) with or without quercetin groups. Fifteen day old embryonated eggs were injected with the abovementioned solutions via the allantoic cavity. On embryonic day 19, the tissues of the embryos were collected for histopathological examination using frozen oil red O staining, RNA extraction, real-time quantitative polymerase chain reaction, and immunohistochemical investigations. The glycogen and lipid contents in the liver increased after LPS stimulation as compared with the PBS group, whereas quercetin decreased the accumulation as compared with the LPS group. The mRNA expressions of AMPKα1 and AMPKα2 in the duodena, ceca, and livers were upregulated after LPS induction as compared with the PBS group, while quercetin could downregulate these expressions as compared with the LPS group. The immunopositivity of AMPKα2 in the villus, crypt, lamina propria, tunica muscularis, and myenteric plexus in the duodena and in the cytoplasms of hepatocytes significantly increased after LPS induction when compared with the PBS group (p < 0.01), whereas the immunopositivity to AMPKα2 in the quercetin treatment group significantly decreased when compared with the LPS group (p < 0.01 or p < 0.05). The LPS-induced high expressions of transcription factor PPARα and glucose transporter (SGLT1) were blocked by quercetin in the duodena, ceca, and livers. Quercetin treatment improved the LPS-induced decrease in APOA4 in the duodena, ceca, and livers. The mRNA expression of PEPT1 in the duodena and ceca increased after LPS challenge, whereas quercetin could downregulate PEPT1 gene expression. These data demonstrate that quercetin improved the energy deficiency induced by LPS in chicken embryos. The LPS-induced inflammation model was established to avoid the effect of LPS exposure from the environment and intestinal flora. The results form the basis the administration of quercetin pretreatment (in ovo infection) to improve the energy state of chicken embryos and improve the inflammation response.

Proteomic analysis of Nipponia nippon (ID#162)

We investigated the proteome of a female Crested Ibis (Nipponia nippon, ID#162) that died on March 10, 2010 at the Sado Japanese Crested Ibis Conservation Center. Protein preparations from the brain, trachea, liver, heart, lung, proventriculus, muscular stomach, small intestine, duodenum, ovary and neck muscle were subjected to in-solution shotgun mass spectrometry (MS)/MS analyses using an LTQ Orbitrap XL mass spectrometer. A search of the National Center for Biotechnology Information Gallus gallus databases revealed 4253 GI (GenInfo Identifier) numbers with the sum of the same 11 tissues examined in the Crested Ibis. To interpret the obtained proteomics data, it was verified in detail with the data obtained from the brain of the Crested Ibis. It has been reported that drebrin A is specifically expressed in adult chicken brain. In the shotgun proteomic analyses of the Crested Ibis, we identified drebrin A as a brain-specific protein. Furthermore, Western blotting analysis of the protein preparations from 10 tissues of the Crested Ibis and 150-day-old hens using anti-drebrin antibodies showed intensive expression of approximately 110 kDa polypeptides of drebrin in both brains. We believe firmly that the present data will contribute to initial and fundamental steps toward understanding the Crested Ibis proteome.

Sequence and comparative analysis of the chicken genome provide unique perspectives on vertebrate evolution

We present here a draft genome sequence of the red jungle fowl, Gallus gallus. Because the chicken is a modern descendant of the dinosaurs and the first non-mammalian amniote to have its genome sequenced, the draft sequence of its genome--composed of approximately one billion base pairs of sequence and an estimated 20,000-23,000 genes--provides a new perspective on vertebrate genome evolution, while also improving the annotation of mammalian genomes. For example, the evolutionary distance between chicken and human provides high specificity in detecting functional elements, both non-coding and coding. Notably, many conserved non-coding sequences are far from genes and cannot be assigned to defined functional classes. In coding regions the evolutionary dynamics of protein domains and orthologous groups illustrate processes that distinguish the lineages leading to birds and mammals. The distinctive properties of avian microchromosomes, together with the inferred patterns of conserved synteny, provide additional insights into vertebrate chromosome architecture.

A vertebrate aldo-keto reductase active with retinoids and ethanol

Enzymes of the short chain and medium chain dehydrogenase/reductase families have been demonstrated to participate in the oxidoreduction of ethanol and retinoids. Mammals and amphibians contain, in the upper digestive tract mucosa, alcohol dehydrogenases of the medium chain dehydrogenase/reductase family, active with ethanol and retinol. In the present work, we searched for a similar enzyme in an avian species (Gallus domesticus). We found that chicken does not contain the homologous enzyme from the medium chain dehydrogenase/reductase family but an oxidoreductase from the aldo-keto reductase family, with retinal reductase and alcohol dehydrogenase activities. The amino acid sequence shows 66-69% residue identity with the aldose reductase and aldose reductase-like enzymes. Chicken aldo-keto reductase is a monomer of M(r) 36,000 expressed in eye, tongue, and esophagus. The enzyme can oxidize aliphatic alcohols, such as ethanol, and it is very efficient in all-trans- and 9-cis-retinal reduction (k(cat)/K(m) = 5,300 and 32,000 mm(-1).min(-1), respectively). This finding represents the inclusion of the aldo-keto reductase family, with the (alpha/beta)(8) barrel structure, into the scenario of retinoid metabolism and, therefore, of the regulation of vertebrate development and tissue differentiation.

Recommended nomenclature for the vertebrate alcohol dehydrogenase gene family

The alcohol dehydrogenase (ADH) gene family encodes enzymes that metabolize a wide variety of substrates, including ethanol, retinol, other aliphatic alcohols, hydroxysteroids, and lipid peroxidation products. Studies on 19 vertebrate animals have identified ADH orthologs across several species, and this has now led to questions of how best to name ADH proteins and genes. Seven distinct classes of vertebrate ADH encoded by non-orthologous genes have been defined based upon sequence homology as well as unique catalytic properties or gene expression patterns. Each class of vertebrate ADH shares <70% sequence identity with other classes of ADH in the same species. Classes may be further divided into multiple closely related isoenzymes sharing >80% sequence identity such as the case for class I ADH where humans have three class I ADH genes, horses have two, and mice have only one. Presented here is a nomenclature that uses the widely accepted vertebrate ADH class system as its basis. It follows the guidelines of human and mouse gene nomenclature committees, which recommend coordinating names across species boundaries and eliminating Roman numerals and Greek symbols. We recommend that enzyme subunits be referred to by the symbol "ADH" (alcohol dehydrogenase) followed by an Arabic number denoting the class; i.e. ADH1 for class I ADH. For genes we recommend the italicized root symbol "ADH" for human and "Adh" for mouse, followed by the appropriate Arabic number for the class; i.e. ADH1 or Adh1 for class I ADH genes. For organisms where multiple species-specific isoenzymes exist within a class, we recommend adding a capital letter after the Arabic number; i.e. ADH1A, ADH1B, and ADH1C for human alpha, beta, and gamma class I ADHs, respectively. This nomenclature will accommodate newly discovered members of the vertebrate ADH family, and will facilitate functional and evolutionary studies.

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.

Alcohol dehydrogenase of class I: kiwi liver enzyme, parallel evolution in separate vertebrate lines, and correlation with 12S rRNA patterns

Alcohol dehydrogenase class I from kiwi liver has been purified, analyzed, and compared with that of other alcohol dehydrogenases. The results show that several avian and mammalian forms of the enzyme exhibit parallel evolutionary patterns in two independent lineages of a single protein, establishing a pattern in common. Furthermore, the data correlate the enzyme evolutionary pattern with that of 12S rRNA. Biologically, the patterns complement those on ratite and other avian relationships. Functionally, the enzyme has a low Km with ethanol and a branched-chain residue at position 141, like the mammalian enzymes but in contrast to the other characterized ratite enzyme (with Ala-141 and a higher Km). This pattern of natural variability suggests a frequent but not fully complete correlation between a large residue size at position 141 and tight ethanol binding.

Alcohol dehydrogenase class III contrasted to class I. Characterization of the cyclostome enzyme, the existence of multiple forms as for the human enzyme, and distant cross-species hybridization

Alcohol dehydrogenases of classes I (the classical liver enzyme) and III (formaldehyde dehydrogenase) constitute a pair of moderately related enzymes (63% residue identity between the human forms) that differ fundamentally in many respects. To elucidate the nature of the differences, we have characterized alcohol dehydrogenase from the most primitive vertebrate line (a cyclostome, Atlantic Hagfish), related that to the multiplicity of the human enzyme, and submitted the enzymes to in vitro hybridization for evaluation of subunit interactions. Three findings illustrate important principles of the enzyme system. First, the alcohol dehydrogenase purified from cyclostomes is a class-III protein, compatible with the facts that cyclostomes constitute the earliest extant vertebrate line and that class III has a distant pre-vertebrate origin. Second, the hagfish enzyme shows multiplicity, with acidic forms in decreasing yield and with amino acid sequences identical between two major isoforms, both aspects constituting properties similar to those of the corresponding human forms. The chemically different subunits are present as homodimers and heterodimers of unmodified and modified subunits, suggesting that the class-III multiplicity derives from modification of a type common to lines as divergent as mammals and cyclostomes. Third, the human enzyme can form cross-species hybrid dimers in vitro with the cod and hagfish or Drosophila class-III enzymes (positional identity with the human form of 82, 76 and 70%, respectively). Hence, the results provide experimental evidence for little class-III divergence in the segments of subunit interactions. The extent of conservation of residues directly involved in the formation of the subunit interface also reveals a clearly different pattern between classes I and III. This highlights separation of divergent forms in an enzyme system, with the constant form (class III) resembling house-keeping enzymes, and exhibiting a correlation between subunit-interacting and substrate-interacting segments.

Diversity of vertebrate class I alcohol dehydrogenase. Mammalian and non-mammalian enzyme functions correlated through the structure of a ratite enzyme

Class I alcohol dehydrogenase has been characterized from ostrich liver in order to evaluate enzyme variability between two independent lines, mammalian forms of class I alcohol dehydrogenase as a group, and a sufficient number of the enzyme from the most recent animal class (Aves, birds) as another. Between the two enzyme groups, patterns are consistent and mutually similar. This indicates conserved metabolic and catalytic properties of class I alcohol dehydrogenase, suggesting its metabolic role to be distinct, in spite of its protein variability. The new structure has a microheterogeneity (position 112, Arg/Cys) in a variable Zn-binding loop. In addition, it also establishes further native variants at active-site positions, including one thus far unique residue at the inner part of the substrate-binding pocket (Ala141), and a replacement at position 271 (giving His271), which is also the site of a human alcohol dehydrogenase gamma 1/gamma 2 isozyme variability. The data correlate with functional differences in catalytic properties, the ostrich enzyme having a comparatively high Km for ethanol (5.9 mM at pH 10), and emphasize the importance of single positions in substrate and coenzyme binding, paralleling isozyme variability with protein variability within the class I enzymes.

Origin of the human alcohol dehydrogenase system: implications from the structure and properties of the octopus protein

In contrast to the multiplicity of alcohol dehydrogenase in vertebrates, a class III type of the enzyme [i.e., a glutathione-dependent formaldehyde dehydrogenase; formaldehyde; NAD+ oxidoreductase (glutathione-formylating), EC 1.2.1.1.] is the only form detectable in appreciable yield in octopus. It is enzymatically and structurally highly similar to the human class III enzyme, with limited overall residue differences (26%) and only a few conservative residue exchanges at the substrate and coenzyme pockets, reflecting "constant" characteristics of this class over wide time periods. It is distinct from the ethanol-active "variable" class I type of the enzyme (i.e., classical liver alcohol dehydrogenase; alcohol:NAD+ oxidoreductase, EC 1.1.1.1). The residue conservation of class III is also spaced differently from that of class I but is typical of that of proteins in general, emphasizing that class I, with divergence at three functional segments, is the form with deviating properties. In spite of the conservation in class III, surface charges differ considerably. The apparent absence of a class I enzyme in octopus and the constant nature of the class III enzyme support the concept of a duplicative origin of the class I line from the ancient class III form. Still more distant relationships define further enzyme lines that have subunits with other properties.

Basic features of class-I alcohol dehydrogenase: variable and constant segments coordinated by inter-class and intra-class variability. Conclusions from characterization of the alligator enzyme

The enzymatic and structural properties of alligator liver alcohol dehydrogenase have been determined. Aliphatic and alicyclic alcohols serve as substrates for this first reptilian form of the enzyme characterized, with Km values decreasing rapidly from methanol to hexanol, as for the human class I enzymes, and a Km of 1.2 mM for ethanol at pH 9.9. The N-terminus of the 374-residue protein chain is acetyl-blocked. The enzyme is related in descending order to class I > III > V > II of the structurally characterized mammalian alcohol dehydrogenases. This observation is compatible with the presence of a I/III ancestral line. Differences of the enzyme classes exceed those of the species, suggesting an early origin of the classes. Within its enzyme class, the reptilian protein is most closely related to the avian form (82% residue identities), and is closer to the human than to the amphibian form (76%, versus 69%, respectively). This establishes class I alcohol dehydrogenase as an enzyme having fairly constant rate of change during much of vertebrate evolution, approximately 10% residue differences/100 million years of separation between pairs compared. Residues interacting with the substrate and coenzyme are largely conserved. In the alligator enzyme, there are only four replacements in the substrate pocket compared with the human class I gamma subunit, and those are not known to have functional roles. These properties account for the kinetic parameters, and suggest distinct metabolic functions for the class I enzyme in vertebrates. Comparisons of the enzymes of the different vertebrate lines reveal that segment patterns are characteristic features of the class I enzymes. Three segments are 'variable', while two are 'constant', and both these types of segment are identical with those of the classes. There is extensive variability in close proximity to the active site of the enzyme and this appears to constitute a fundamental property of class I liver alcohol dehydrogenases in general.

Purification and partial amino acid sequence of a high-activity human stomach alcohol dehydrogenase

To understand the relative importance of alcohol dehydrogenase (ADH) isoenzymes in gastric ethanol metabolism, a stomach-specific ADH (sigma-ADH) was purified to homogeneity from human transplant donor and surgical tissues, and its activity for ethanol oxidation was examined. The enzyme from these tissues had a specific activity at pH 10 of approximately 70 units/mg, about 10 times that reported by Moreno and Parés (J. Biol. Chem. 266:1128-1133, 1991). The enzyme exhibited a high Km for ethanol at pH 7.5 and 10 (29 and 5.2 mM, respectively). This high-activity sigma-ADH isoenzyme migrated on starch and isoelectric focusing gels to a position slightly anodic to the liver pi pi isoenzyme. It was subjected to digestion by endoproteinases, and approximately 40% of the protein was sequenced. The sigma-ADH exhibited 75%, 68%, and 62% sequence identity to the human class I (beta 1), II (pi), and III (chi) isoenzymes, respectively, and 61% identity to the deduced ADH6 amino acid sequence. Phylogenetic analysis indicated that precursors to this high-activity sigma-ADH and the class I isoenzymes diverged more recently than precursors to the class II and III isoenzymes, after reptilian and avian divergence. The high-activity sigma-ADH isoenzyme therefore represents a distinct class of ADH (class IV), more closely related in evolution to the class I isoenzymes than to the other known human isoenzymes.

Mutation of Arg-115 of human class III alcohol dehydrogenase: a binding site required for formaldehyde dehydrogenase activity and fatty acid activation

The origin of the fatty acid activation and formaldehyde dehydrogenase activity that distinguishes human class III alcohol dehydrogenase (alcohol:NAD+ oxidoreductase, EC 1.1.1.1) from all other alcohol dehydrogenases has been examined by site-directed mutagenesis of its Arg-115 residue. The Ala- and Asp-115 mutant proteins were expressed in Escherichia coli and purified by affinity chromatography and ion-exchange HPLC. The activities of the recombinant native and mutant enzymes toward ethanol are essentially identical, but mutagenesis greatly decreases the kcat/Km values for glutathione-dependent formaldehyde oxidation. The catalytic efficiency for the Asp variant is < 0.1% that of the unmutated enzyme, due to both a higher Km and a lower kcat value. As with the native enzyme, neither mutant can oxidize methanol, be saturated by ethanol, or be inhibited by 4-methylpyrazole; i.e., they retain these class III characteristics. In contrast, however, their activation by fatty acids, another characteristic unique to class III alcohol dehydrogenase, is markedly attenuated. The Ala mutant is activated only slightly, but the Asp mutant is not activated at all. The results strongly indicate that Arg-115 in class III alcohol dehydrogenase is a component of the binding site for activating fatty acids and is critical for the binding of S-hydroxymethylglutathione in glutathione-dependent formaldehyde dehydrogenase activity.

Progressive sequence alignment and molecular evolution of the Zn-containing alcohol dehydrogenase family

Sequences of 47 members of the Zn-containing alcohol dehydrogenase (ADH) family were aligned progressively, and an evolutionary tree with detailed branch order and branch lengths was produced. The alignment shows that only 9 amino acid residues (of 374 in the horse liver ADH sequence) are conserved in this family; these include eight Gly and one Val with structural roles. Three residues that bind the catalytic Zn and modulate its electrostatic environment are conserved in 45 members. Asp 223, which determines specificity for NAD, is found in all but the two NADP-dependent enzymes, which have Gly or Ala. Ser or Thr 48, which makes a hydrogen bond to the substrate, is present in 46 members. The four Cys ligands for the structural zinc are conserved except in zeta-crystallin, the sorbitol dehydrogenases, and two bacterial enzymes. Analysis of the evolutionary tree gives estimates of the times of divergence for different animal ADHs. The human class II (pi) and class III (chi) ADHs probably diverged about 630 million years ago, and the newly identified human ADH6 appeared about 520 million years ago, implying that these classes of enzymes may exist or have existed in all vertebrates. The human class I ADH isoenzymes (alpha, beta, and gamma) diverged about 80 million years ago, suggesting that these isoenzymes may exist or have existed in all primates. Analysis of branch lengths shows that these plant ADHs are more conserved than the animal ones and that class III ADHs are more conserved than class I ADHs. The rate of acceptance of point mutations (PAM units) shows that selection pressure has existed for ADHs, implying that these enzymes play definite metabolic roles.

Estrogen induction of alcohol dehydrogenase in the uropygial gland of mallard ducks

Treatment of mallard ducks with estradiol, or a combination of estradiol and thyroxine, has been shown to result in the proliferation of peroxisomes and production of diesters of 3-hydroxy fatty acids, the female pheromones, in the uropygial gland of male and female mallard ducks. Such a treatment results in the induction of a unique set of proteins. A cDNA library enriched in hormone-induced transcripts was subjected to differential screening. The nucleotide sequence of one of the two unique cDNA clones, DGH1, had high similarity to the Human class I alcohol dehydrogenase (ADH) gamma subunit and represented the carboxy-terminus of the protein from amino acid 190-374. SDS/PAGE and Western blot analysis of the proteins indicated that the level of a 38-kDa protein that cross-reacted with antibodies prepared against the chicken ADH was increased 5-7-fold by hormone treatment. Assays for ADH activity in the uropygial gland extracts of male mallards showed a 5-7-fold induction of the enzyme by hormone treatment. The 1.9-kb ADH mRNA levels were increased 12-14-fold under these conditions. Of all the tissues tested, the uropygial gland had the highest levels of ADH mRNA. Induction of ADH by estradiol treatment occurred only in this tissue. Elevated levels of ADH were also observed in the glands of male mallards in eclipse, the post-nuptial condition when the hormonal balance is shifted to higher estrogen levels, suggesting that this enzyme is regulated by estrogens in this period. Estradiol treatment caused an 80% decrease in the NAD+/NADH ratio in the uropygial gland and a twofold increase in the fatty alcohol oxidation rate catalyzed by the gland extract. These observations could help explain how increased levels of ADH could contribute to the production of the diesters.

Amphibian alcohol dehydrogenase, the major frog liver enzyme. Relationships to other forms and assessment of an early gene duplication separating vertebrate class I and class III alcohol dehydrogenases

Submammalian alcohol dehydrogenase structures can be used to evaluate the origins and functions of the different types of the mammalian enzyme. Two avian forms were recently reported, and we now define the major amphibian alcohol dehydrogenase. The enzyme from the liver of the Green frog Rana perezi was purified, carboxymethylated, and submitted to amino acid sequence determination by peptide analysis of six different digests. The protein has a 375-residue subunit and is a class I alcohol dehydrogenase, bridging the gap toward the original separation of the classes that are observable in the human alcohol dehydrogenase system. In relation to the human class I enzyme, the amphibian protein has residue identities exactly halfway (68%) between those for the corresponding avian enzyme (74%) and the human class III enzyme (62%), suggesting an origin of the alcohol dehydrogenase classes very early in or close to the evolution of the vertebrate line. This conclusion suggests that these enzyme classes are more universal among animals than previously realized and constitutes the first real assessment of the origin of the duplications leading to the alcohol dehydrogenase classes. Functionally, the amphibian enzyme exhibits properties typical for class I but has an unusually low Km for ethanol (0.09 mM) and Ki for pyrazole (0.15 microM) at pH 10.0. This correlates with a strictly hydrophobic substrate pocket and one amino acid difference toward the human class I enzyme at the inner part of the pocket. Coenzyme binding is highly similar, while subunit-interacting residues, as in other alcohol dehydrogenases, exhibit several differences.(ABSTRACT TRUNCATED AT 250 WORDS)