Structural features of stomach aldehyde dehydrogenase distinguish dimeric aldehyde dehydrogenase as a 'variable' enzyme. 'Variable' and 'constant' enzymes within the alcohol and aldehyde dehydrogenase families

Medium- and short-chain dehydrogenase/reductase gene and protein families : the MDR superfamily

The MDR superfamily with ~350-residue subunits contains the classical liver alcohol dehydrogenase (ADH), quinone reductase, leukotriene B4 dehydrogenase and many more forms. ADH is a dimeric zinc metalloprotein and occurs as five different classes in humans, resulting from gene duplications during vertebrate evolution, the first one traced to ~500 MYA (million years ago) from an ancestral formaldehyde dehydrogenase line. Like many duplications at that time, it correlates with enzymogenesis of new activities, contributing to conditions for emergence of vertebrate land life from osseous fish. The speed of changes correlates with function, as do differential evolutionary patterns in separate segments. Subsequent recognitions now define at least 40 human MDR members in the Uniprot database (corresponding to 25 genes when excluding close homologues), and in all species at least 10888 entries. Overall, variability is large, but like for many dehydrogenases, subdivided into constant and variable forms, corresponding to household and emerging enzyme activities, respectively. This review covers basic facts and describes eight large MDR families and nine smaller families. Combined, they have specific substrates in metabolic pathways, some with wide substrate specificity, and several with little known functions.

Primary structure of human hepatocellular carcinoma-associated aldehyde dehydrogenase

Tumor-associated aldehyde dehydrogenase (T-ALDH) is strongly expressed in hepatocellular carcinoma (HCC) but undetectable in normal liver. In the present study, this enzyme from human HCC, HCC T-ALDH, was purified and the partial amino acid sequences (384 residues) determined by direct protein sequencing matched the amino acid sequence (453 residues) deduced from cloned HCC T-ALDH cDNAs with an open reading frame. The coding sequences of HCC T-ALDH cDNA, human stomach ALDH3A1 cDNA [Hsu et al., J. Biol. Chem. 267 (1992) 3030-3037] and human squamous cell carcinoma (SCC) T-ALDH cDNA (Schuuring et al., GenBank I.D. M74542) matched one another except for discrepancies at four positions, with consequent P12R, I27F and S134A substitutions. R and A were found in HCC and SCC T-ALDHs, whereas P and S were present in stomach ALDH3A1. To confirm that these discrepancies would have general occurrence, coding sequences of HCC T-ALDH cDNAs from six patients and stomach ALDH3A1 cDNAs from two individuals were examined and all were found to encode ALDH3A1 having R, I and A at protein positions 12, 27 and 134, respectively, indicating HCC T-ALDH to be variant ALDH3A1 which is common in human stomach tissues.

Aldehyde dehydrogenase from rat intestinal mucosa: purification and characterization of an isozyme with high affinity for gamma-aminobutyraldehyde

In rat adrenal gland and gastric mucosa putrescine is efficiently oxidized to GABA via gamma-aminobutyraldehyde (ABAL) by action of diamine oxidase and aldehyde dehydrogenase. Having turned our attention on the rat intestinal mucosa, where putrescine uptake and diamine oxidase are active, we have purified and characterized an aldehyde dehydrogenase optimally active on gamma-aminobutyraldehyde. A dimer with a subunit molecular weight of 52,000, the native enzyme binds ABAL and NAD+ with high affinity: at pH 7.4, Km values are equal to 18 and 14 microM, respectively. Affinity for betaine aldehyde is much lower (Km = 285 microM), but the efficiency is equally good, thanks to a high value of V. Unaffected by disulfiram and Mg2+, the enzyme is activated by high NAD+ concentrations (Vnn = 1.6 x Vn) and is competitively inhibited by NADH. According to the best fitting model, the dimeric enzyme only binds one NADH and the mixed complex enzyme-NAD(+)-NADH is inactive. The increase of activity promoted by NAD+ can therefore be ascribed to an allosteric effect, rather than to the activation of a second reaction center. Highly stable at pH 6.8 in the presence of dithiothreitol and high phosphate concentrations, ABALDH is inactivated by ion-exchange resins and by cationic buffers. Our results show that the enzyme can be effectively involved in the metabolism of biogenic amines and, with a K(m) for ABAL lower than 20 microM, in the synthesis of GABA.

Structure of betaine aldehyde dehydrogenase at 2.1 A resolution

The three-dimensional structure of betaine aldehyde dehydrogenase, the most abundant aldehyde dehydrogenase (ALDH) of cod liver, has been determined at 2.1 A resolution by the X-ray crystallographic method of molecular replacement. This enzyme represents a novel structure of the highly multiple ALDH, with at least 12 distinct classes in humans. This betaine ALDH of class 9 is different from the two recently determined ALDH structures (classes 2 and 3). Like these, the betaine ALDH structure has three domains, one coenzyme binding domain, one catalytic domain, and one oligomerization domain. Crystals grown in the presence or absence of NAD+ have very similar structures and no significant conformational change occurs upon coenzyme binding. This is probably due to the tight interactions between domains within the subunit and between subunits in the tetramer. The oligomerization domains link the catalytic domains together into two 20-stranded pleated sheet structures. The overall structure is similar to that of the tetrameric bovine class 2 and dimeric rat class 3 ALDH, but the coenzyme binding with the nicotinamide in anti conformation, resembles that of class 2 rather than of class 3.

Class 2 aldehyde dehydrogenase. Characterization of the hamster enzyme, sensitive to daidzin and conserved within the family of multiple forms

Mitochondrial (class 2) hamster aldehyde dehydrogenase has been purified and characterized. Its primary structure has been determined and correlated with the tertiary structure recently established for this class from another species. The protein is found to represent a constant class within a complex family of multiple forms. Variable segments that occur in different species correlate with non-functional segments, in the same manner as in the case of the constant class of alcohol dehydrogenases (class III type) of another protein family, but distinct from the pattern of the corresponding variable enzymes. Hence, in both these protein families, overall variability and segment architectures behave similarly, with at least one 'constant' form in each case, class III in the case of alcohol dehydrogenases, and at least class 2 in the case of aldehyde dehydrogenases.

Fructose-1,6-bisphosphatase. Primary structure of the rabbit liver enzyme. 'Intermediate' variability of an oligomeric protein

The primary structure of rabbit liver fructose-1,6-bisphosphatase was determined by peptide analysis of digests with different proteases. The results establish the primary structure, complete data bank entries, and show that this enzyme variant is indeed homologous with other liver fructose-1,6-bisphosphatases. Residue differences with the enzymes from other mammals are 9-15%, with those from plants and yeasts about 50%, and with those from characterized prokaryotes up to 70%, showing an enzyme variability intermediate between those of 'variable' and 'constant' oligomeric dehydrogenases. Structural relationships, conformations and catalytic mechanisms are consistent within the family of fructose-1,6-bisphosphatases, and the rabbit protein is a typical rather than an aberrant form of the enzyme.

The vertebrate alcohol dehydrogenase system: variable class II type form elucidates separate stages of enzymogenesis

A mixed-class alcohol dehydrogenase has been characterized from avian liver. Its functional properties resemble the classical class I type enzyme in livers of humans and animals by exhibiting low Km and kcat values with alcohols (Km = 0.7 mM with ethanol) and low Ki values with 4-methylpyrazole (4 microM). These values are markedly different from corresponding parameters of class II and III enzymes. In contrast, the primary structure of this avian liver alcohol dehydrogenase reveals an overall relationship closer to class II and to some extent class III (69 and 65% residue identities, respectively) than to class I or the other classes of the human alcohol dehydrogenases (52-61%), the presence of an insertion (four positions in a segment close to position 120) as in class II but in no other class of the human enzymes, and the presence of several active site residues considered typical of the class II enzyme. Hence, the avian enzyme has mixed-class properties, being functionally similar to class I, yet structurally similar to class II, with which it also clusters in phylogenetic trees of characterized vertebrate alcohol dehydrogenases. Comparisons reveal that the class II enzyme is approximately 25% more variable than the "variable" class I enzyme, which itself is more variable than the "constant" class III enzyme. The overall extreme, and the unusual chromatographic behavior may explain why the class II enzyme has previously not been found outside mammals. The properties define a consistent pattern with apparently repeated generation of novel enzyme activities after separate gene duplications.

Purification and kinetic characterization of gamma-aminobutyraldehyde dehydrogenase from rat liver

Oxidative deamination of putrescine, the precursor of polyamines, gives rise to gamma-aminobutyraldehyde (ABAL). In this study an aldehyde dehydrogenase, active on ABAL, has been purified to electrophoretic homogeneity from rat liver cytoplasm and its kinetic behaviour investigated. The enzyme is a dimer with a subunit molecular weight of 51,000. It is NAD(+)-dependent, active only in the presence of sulphhydryl compounds and has a pH optimum in the range 7.3-8.4. Temperatures higher than 28 degrees C promote slow activation and the process is favoured by the presence of at least one substrate. Km for aliphatic aldehydes decreases from 110 microM for ABAL and acetaldehyde to 2-3 microM for capronaldehyde. The highest relative V-values have been observed with ABAL (100) and isobutyraldehyde (64), and the lowest with acetaldehyde (14). Affinity for NAD+ is affected by the aldehyde present at the active site: Km for NAD+ is approximately 70 microM with ABAL, approximately 200 microM with isobutyraldehyde and capronaldehyde, and > 800 microM with acetaldehyde. The kinetic behaviour at 37 degrees C is quite complex; according to enzymatic models, NAD+ activates the enzyme (Kact approximately 500 microM) while NADH competes for the regulatory site (Kin approximately 70 microM). In the presence of high NAD+ concentrations (4 mM), ABAL promotes further activation by binding to a low-affinity regulatory site (Kact approximately 10 mM). The data show that the enzyme is probably an E3 aldehyde dehydrogenase, and suggest that it can effectively metabolize aldehydes arising from biogenic amines.

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.

Mammalian class IV alcohol dehydrogenase (stomach alcohol dehydrogenase): structure, origin, and correlation with enzymology

The structure of a mammalian class IV alcohol dehydrogenase has been determined by peptide analysis of the protein isolated from rat stomach. The structure indicates that the enzyme constitutes a separate alcohol dehydrogenase class, in agreement with the distinct enzymatic properties; the class IV enzyme is somewhat closer to class I (the "classical" liver alcohol dehydrogenase; approximately 68% residue identities) than to the other classes (II, III, and V; approximately 60% residue identities), suggesting that class IV might have originated through duplication of an early vertebrate class I gene. The activity of the class IV protein toward ethanol is even higher than that of the classical liver enzyme. Both Km and kcat values are high, the latter being the highest of any class characterized so far. Structurally, these properties are correlated with replacements at the active site, affecting both substrate and coenzyme binding. In particular, Ala-294 (instead of valine) results in increased space in the middle section of the substrate cleft, Gly-47 (instead of a basic residue) results in decreased charge interactions with the coenzyme pyrophosphate, and Tyr-363 (instead of a basic residue) may also affect coenzyme binding. In combination, these exchanges are compatible with a promotion of the off dissociation and an increased turnover rate. In contrast, residues at the inner part of the substrate cleft are bulky, accounting for low activity toward secondary alcohols and cyclohexanol. Exchanges at positions 259-261 involve minor shifts in glycine residues at a reverse turn in the coenzyme-binding fold. Clearly, class IV is distinct in structure, ethanol turnover, stomach expression, and possible emergence from class I.

Variability patterns of dehydrogenases versus peptide hormones and proteases/antiproteases

Comparisons of human/rat species variants of 23 dehydrogenases versus 41 entries for peptide hormones and 41 for proteases/antiproteases reveal characteristic patterns. Dehydrogenases are 'constant' (2-8% residue differences between homologues) or 'variable' (12-40% differences). Peptide hormones exhibit a wider range, with many 'strictly conserved' and others spreading upscale, while proteases/antiproteases are overall shifted upscale, with few 'constant' and many 'variable'. Overall, the influence of polypeptide size and function is confirmed, while for the dehydrogenases, the data highlight the 'constant' pattern as the one with high frequency values and suggest for classic liver alcohol dehydrogenase the 'variable' pattern to correlate with emerging functions.

Cephalopod alcohol dehydrogenase: purification and enzymatic characterization

Octopus, squid and cuttle-fish organs were examined for alcohol dehydrogenase activity. Only one form was detectable, with properties typical of mammalian class III alcohol dehydrogenase. The corresponding protein was purified from octopus and enzymatically characterized. Ion-exchange and affinity chromatography produced a pure protein in excellent yield (73%) after 1600-fold purification. Enzymatic parameters with several substrates were similar to those for the human class III alcohol dehydrogenase, demonstrating a largely conserved function of the enzyme through wide lines of divergence covering vertebrates, cephalopods and bacteria. The results establish the universal occurrence of class III alcohol dehydrogenase and its strictly conserved functional properties in separate living forms. The absence of other alcohol dehydrogenases in cephalopods is compatible with the emergence of the ethanol-active class I type at a later stage, in lineages leading to vertebrates.

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.

Regulation by progesterone and pregnenolone of dimeric aldehyde dehydrogenase from rat testis cytoplasm

1. Aldehyde dehydrogenase from rat testis cytosol has been purified to electrophoretic homogeneity. With an isoelectric point of 9.5, the enzyme appears a dimer with a subunit molecular weight of 52,500. 2. The influence of pregnenolone and progesterone on the kinetic behaviour has been investigated using valeraldehyde as substrate. 3. The kinetic data were fitted to a modified version of the Monod-Wyman-Changeux model and the fitting procedure resulted in a good correspondence between theoretical and experimental reaction rates over a wide range of valeraldehyde concentrations. 4. According to the model, the dimeric enzyme is in equilibrium between two conformational states R and T. The R state displays higher affinity for valeraldehyde, but lower catalytic power. In the absence of substrates and effectors the [T]/[R] ratio is near to 1. 5. Pregnenolone and progesterone activate the enzyme by stabilizing the more active state T and by increasing the catalytic power of the R state. The increase of activity is counteracted by the inhibition exerted by both steroids on the T state.

Dual relationships of xylitol and alcohol dehydrogenases in families of two protein types

Xylitol dehydrogenase encoded by gene XYL2 from Pichia stipitis is a member of the medium-chain alcohol dehydrogenase family, as evidenced by the domain organization and a distant homology (24% residue identity with the human class I gamma 1 alcohol dehydrogenase). Much of a loop structure is missing, like in mammalian sorbitol and prokaryotic threonine dehydrogenases, many additional differences occur, and relationships are closest with the sorbitol dehydrogenase, the equivalence of which in P. stipitis may actually be the xylitol dehydrogenase. A second P. stipitis gene, also cloned and corresponding to a xylitol dehydrogenase, is highly different from XYL2, but encodes an enzyme with structural properties typical of the short-chain dehydrogenase family, which also contains an alcohol dehydrogenase (from Drosophila). Thus, yeast xylitol dehydrogenases, like alcohol and polyol dehydrogenases from other sources, have dual derivations, combining similar enzyme activities in separate protein families. In contrast to the situation with the other enzymes, both forms of xylitol dehydrogenase are present in one organism.

Zeta-crystallin versus other members of the alcohol dehydrogenase super-family. Variability as a functional characteristic

Species variability of the lens protein zeta-crystallin was correlated with those of alcohol dehydrogenases of classes I and III and sorbitol dehydrogenase in the same protein family. The extent of overall variability, nature of residues conserved, and patterns of segment variability, all fall within the limits typical of the 'variable' group of medium-chain alcohol dehydrogenases. This shows that zeta-crystallin is subject to restrictions similar to those of classical liver alcohol dehydrogenase and therefore derived from a metabolically active enzyme like other enzyme crystallins. Special residues at the active site, however, differ substantially, including an apparent lack of a zinc-binding site. This is compatible with altered functional properties and makes the spread within this medium-chain dehydrogenase family resemble the wide spread within the short-chain dehydrogenases. Schematic plotting is useful for illustrating the differences between 'variable' and 'constant' enzymes.

Alcohol and aldehyde dehydrogenases in human esophagus: comparison with the stomach enzyme activities

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) isoenzymes from surgical esophageal and gastric mucosa were compared by agarose isoelectric focusing. Two prominent ADH forms, designated mu 1 (equivalent to the recently reported mu-form) and mu 2, were expressed in all the 15 esophagus specimens studied, whereas only four of seven examined gastric specimens exhibited a weak to moderately strong mu 1-ADH activity band on the isoelectric focusing gels. pI values of the esophageal mu 1-ADH and mu 2-ADH, and the liver pi-ADH were determined to be 8.61, 8.13, and 8.90, respectively. mu-ADHs exhibited high Km for ethanol (12 mM) and low sensitivity to 4-methylpyrazole inhibition. ALDH3 (BB form) and ALDH1 were the major high- and low-Km aldehyde dehydrogenase in the esophagus, respectively. The ADH and ALDH activities were determined at pH 7.5 to be 751 +/- 78 and 29.9 +/- 3.0 nmol/min/g tissue, respectively (measured at 500 mM ethanol or at 200 microM acetaldehyde; mean +/- SEM; N = 15). The esophageal ADH activity was approximately 4-fold and the ALDH activity 20% that of the stomach enzyme. Because the presence of high activity and high Km mu-ADHs as well as low-activity ALDH1 were found in human esophageal mucosa, it is suggested that there may exist an accumulation of intracellular acetaldehyde during alcohol ingestion. This reactive and toxic metabolite may be involved in the pathogenesis of alcohol-induced esophageal disorders.

Isozyme developments in mammalian class-I alcohol dehydrogenase. cDNA cloning, functional correlations, and lack of evidence for genetic isozymes in rabbit

Isozyme patterns differ widely among the classical type (class I) of mammalian alcohol dehydrogenases. For the rabbit enzyme, the possibility of isozymes has been reported but structural evidence is lacking. This system was now studied at both the mRNA/cDNA and protein levels. Ten cDNA clones, coding for class-I alcohol dehydrogenase, were isolated from a rabbit liver cDNA library using a human DNA fragment as probe. The cDNA spanned 1296 bp, including the entire coding region. All clones coded for the same polypeptide and Northern blots identified a single mRNA corresponding to about 1.5 kb. Comparison of two protein forms (CC and BC) by HPLC peptide fingerprinting and structural analysis revealed peptide segments identical in amino acid sequence. Consequently, direct protein analyses and Northern blots show the presence of only one primary translation product. The data suggest that lagomorphic alcohol dehydrogenase, like the rodent enzyme, is not as isozyme rich as it may appear superficially, and that secondary modifications contribute substantially to mammalian alcohol dehydrogenase multiplicity. The active center of the rabbit enzyme suggests similarities to the horse S, human gamma, and rat enzyme structures, compatible with a steroid dehydrogenase activity shown experimentally. Typical class-I properties were established by direct analysis and confirmed by structural properties (Km for cyclohexanol 0.8-1.1 mM, for ethanol 1.6-1.9 mM). The isozyme versus species differences mark the variability of class-I alcohol dehydrogenase versus class III and suggest a parallelism between rapid mutational differences and frequent duplicatory events.

NAD-linked, factor-dependent formaldehyde dehydrogenase or trimeric, zinc-containing, long-chain alcohol dehydrogenase from Amycolatopsis methanolica

NAD-linked, factor-dependent formaldehyde dehydrogenase (FD-FA1DH) of the Gram-positive methylotrophic bacterium, Amycolatopsis methanolica, was purified to homogeneity. It is a trimeric enzyme with identical subunits (molecular mass 40 kDa) containing 6 atoms Zn/enzyme molecule. The factor is a heat-stable, low-molecular-mass compound, which showed retention on an Aminex HPX-87H column. Inactivation of the factor occurred during manipulation, but activity could be restored by incubation with dithiothreitol. The identity of the factor is still unknown. It could not be replaced by thiol compounds or cofactors known to be involved in metabolism of C1 compounds. Of the aldehydes tested, only formaldehyde was a substrate. However, the enzyme showed also activity with higher aliphatic alcohols and the presence of the factor was not required for this reaction. Methanol was not a substrate, but high concentrations of it could replace the factor in the conversion of formaldehyde. Presumably, a hemiacetal of formaldehyde is the genuine substrate, which, in the case of methanol, acts as a factor leading to methylformate as the product. This view is supported by the fact that formate could only be detected in the reaction mixture after acidification. Inhibition studies revealed that the enzyme contains a reactive thiol group, being protected by the binding of NAD against attack by heavy-metal ions and aldehydes. Studies on the effect of the order of addition of coenzyme and substrate suggested that optimal catalysis required NAD as the first binding component. Substrate specificity and the induction pattern clearly indicate a role of the enzyme in formaldehyde oxidation. However, since FD-FA1DH was also found in A. methanolica grown on n-butanol, but not on ethanol, it may have a role in the oxidation of higher aliphatic alcohols as well. FD-FA1DH and the factor from A. methanolica are very similar to a combination already described for Rhodococcus erythropolis [Eggeling, L. & Sahm, H. (1985) Eur. J. Biochem. 150, 129-134]. NAD-linked, glutathione-dependent formaldehyde dehydrogenase (GD-FA1DH) resembles FD-FA1DH in many respects. Since glutathione has so far not been detected in Gram-positive bacteria, FD-FA1DH could be the counterpart of this enzyme in Gram-positive bacteria. Alignment of the N-terminal sequence (31 residues) of FD-FA1DH with that of GD-FA1DH from rat liver indeed showed similarity (30% identical positions). However, comparable similarity was found with class I alcohol dehydrogenase from this organism and with cytosolic alcohol dehydrogenase from Saccharomyces cerevisiae, isozyme 1.(ABSTRACT TRUNCATED AT 400 WORDS)

Class IV alcohol dehydrogenase (the gastric enzyme). Structural analysis of human sigma sigma-ADH reveals class IV to be variable and confirms the presence of a fifth mammalian alcohol dehydrogenase class

Human gastric alcohol dehydrogenase (sigma sigma-ADH) was submitted to peptide analysis at picomole scale. A total of 72 positions were determined in the protein chain, providing information on three aspects of alcohol dehydrogenase structures in general. First, the data establish the presence of a unique class of the enzyme, now confirmed as class IV, expressed in gastric tissue and separate from another novel class, now termed class V. Second, the class IV gastric enzyme has active site relationships compatible with an ethanol-active, zinc-containing alcohol dehydrogenase. Third, this enzyme class is of the variable type, like that for the 'variable', classical liver alcohol dehydrogenase of class I, and in contrast to that for the 'constant' class III enzyme. Known human alcohol dehydrogenase structures now prove the presence of at least seven human genes for the enzyme and nine for the whole protein family.

Taxon-specific recruitment of enzymes as major soluble proteins in the corneal epithelium of three mammals, chicken, and squid

Studies of others have shown that class 3 aldehyde dehydrogenase is a major component of the epithelial cells of the mammalian cornea. Here we demonstrate by peptide sequencing that other major proteins of the corneal epithelium are also identical or related to enzymes in the human, mouse, kangaroo, chicken, and squid. Aldehyde dehydrogenase class 3 was found to be the major protein of human, mouse, and kangaroo corneal epithelial cells. Peptidyl prolyl cis-trans isomerase (cyclophilin) or a homologue thereof is strikingly abundant in the corneal epithelial cells of chicken, but not mammals, and appears to be absent from the cornea of squid. By contrast, enolase or its homologue is relatively abundant in both the mammalian and chicken corneal epithelial cells. In some instances, abundant enzymes are common to cornea and lens in the same species--for example, arginino-succinate lyase/delta 1-crystallin in the chicken and glutathione S-transferase-like protein in the squid; in other cases, the abundant proteins in the cornea have not been found as lens crystallins in any species--for example, aldehyde dehydrogenase class 3 and cyclophilin. These data suggest that enzymes and certain enzyme-crystallins have been recruited as major corneal proteins in a taxon-specific manner and may serve structural rather than, or as well as, enzymatic roles in corneal epithelial cells.

Reptilian alcohol dehydrogenase. Heterogeneity relevant to class multiplicity of the mammalian enzyme

Liver alcohol dehydrogenase of the ethanol-active type ('class I enzyme') from the lizard, Uromastix hardwickii, was purified and screened for relationships with other vertebrate forms of the enzyme. Two different acetylated N-termini (acetyl-Gly and acetyl-Ser) and further positional differences already in the N-terminal segments establish the presence of two types of protein chain. The multiplicity is different from that hitherto detected within vertebrate class I alcohol dehydrogenase isozymes but typical of that which would be expected for subunits of different classes. In particular, relationships to class II or to class II-related forms appear likely. This may indicate yet further vertebrate alcohol dehydrogenase multiplicity or discovery of a class II non-mammalian enzyme. The results give prospects of defining gene duplications corresponding to more than one alcohol dehydrogenase class split to at an early vertebrate stage.

Aldehyde dehydrogenases and their role in carcinogenesis

Aldehydes are highly reactive molecules that may have a variety of effects on biological systems. They can be generated from a virtually limitless number of endogenous and exogenous sources. Although some aldehyde-mediated effects such as vision are beneficial, many effects are deleterious, including cytotoxicity, mutagenicity, and carcinogenicity. A variety of enzymes have evolved to metabolize aldehydes to less reactive forms. Among the most effective pathways for aldehyde metabolism is their oxidation to carboxylic acids by aldehyde dehydrogenases (ALDHs). ALDHs are a family of NADP-dependent enzymes with common structural and functional features that catalyze the oxidation of a broad spectrum of aliphatic and aromatic aldehydes. Based on primary sequence analysis, three major classes of mammalian ALDHs--1, 2, and 3--have been identified. Classes 1 and 3 contain both constitutively expressed and inducible cytosolic forms. Class 2 consists of constitutive mitochondrial enzymes. Each class appears to oxidize a variety of substrates that may be derived either from endogenous sources such as amino acid, biogenic amine, or lipid metabolism or from exogenous sources, including aldehydes derived from xenobiotic metabolism. Changes in ALDH activity have been observed during experimental liver and urinary bladder carcinogenesis and in a number of human tumors, including some liver, colon, and mammary cancers. Changes in ALDH define at least one population of preneoplastic cells having a high probability of progressing to overt neoplasms. The most common change is the appearance of class 3 ALDH dehydrogenase activity in tumors arising in tissues that normally do not express this form. The changes in enzyme activity occur early in tumorigenesis and are the result of permanent changes in ALDH gene expression. This review discusses several aspects of ALDH expression during carcinogenesis. A brief introduction examines the variety of sources of aldehydes. This is followed by a discussion of the mammalian ALDHs. Because the ALDHs are a relatively understudied family of enzymes, this section presents what is currently known about the general structural and functional properties of the enzymes and the interrelationships of the various forms. The remainder of the review discusses various aspects of the ALDHs in relation to tumorigenesis. The expression of ALDH during experimental carcinogenesis and what is known about the molecular mechanisms underlying those changes are discussed. This is followed by an extended discussion of the potential roles for ALDH in tumorigenesis. The role of ALDH in the metabolism of cyclophosphamidelike chemotherapeutic agents is described. This work suggests that modulation of ALDH activity may an important determinant of the effectiveness of certain chemotherapeutic agents.(ABSTRACT TRUNCATED AT 400 WORDS)