cDNA sequence of human class III alcohol dehydrogenase

A human placental cDNA library was screened using oligonucleotide probes based on the peptide sequence of the human class III alcohol dehydrogenase. An incomplete cDNA clone covering most of the coding sequence of class III alcohol dehydrogenase was isolated from a human placental cDNA library. This was subsequently used as a probe to obtain a full-length clone from a human testicular library. The cDNA sequence codes for a protein that is identical to the enzyme purified from human liver. Southern analysis of human genomic DNA suggests that it may contain more than a single copy per haploid genome.     

A human liver alcohol dehydrogenase enzyme-linked immunosorbent assay method specific for class I, II, and III isozymes

A sensitive and convenient method for the quantitative measurement of human alcohol dehydrogenase (ADH) isozymes based on enzyme-linked immunosorbent assay has been devised. The procedure was optimized with respect to antigen coating density, antiserum dilution, and incubation times with rabbit antisera raised against beta 1 beta 1-ADH to achieve a limit of sensitivity of 1 ng/ml for this isozyme when purified. Using the optimal conditions established, quantitative measurement of alpha beta 1, alpha gamma 1, beta 1 gamma 1, pi, and chi-ADH were obtained with antisera raised in rabbits toward these individual isozymes. The incorporation into the procedure of thimerosal (ethyl(4-mercaptobenzoato-S)mercury) or other sulfhydryl specific reagents improved the soluble phase antiserum avidity for all ADH isozymes, thereby increasing the sensitivity. Thimerosal is an absolute requirement for chi-ADH antigen-antibody binding. The polyclonal rabbit antisera elicited by the individual isozymes of the three classes of ADH exhibit a high degree of isozyme class specificity. Cross-reactivity of the antibodies with the beta 1 beta 1, alpha gamma 1, alpha gamma 2, alpha beta 1, beta 1 gamma 1, beta 1 gamma 2, pi and chi isozymes were evaluated. Antisera against the class I isozymes beta 1 beta 1 and beta 1 gamma 1 cross-react with all class I isozymes and with pi-ADH. Antibodies against pi and chi-ADH are selective and specific only for their respective antigens. Neither one cross-reacts with any class I isozyme. Conformational effects resulting from subunit interactions likely account for differences in cross-immunoreactivity between the closely homologous class I isozymes.     

Class III human liver alcohol dehydrogenase: a novel structural type equidistantly related to the class I and class II enzymes

The primary structure of class III alcohol dehydrogenase (dimeric with chi subunits) from human liver has been determined by peptide analyses. The protein chain is a clearly distinct type of subunit distantly related to those of both human class I and class II alcohol dehydrogenases (with alpha, beta, gamma, and pi subunits, respectively). Disregarding a few gaps, residue differences in the chi protein chain with respect to beta 1 and pi occur at 139 and 140 positions, respectively. Compared to class I, the 373-residue chi structure has an extra residue, Cys after position 60, and two missing ones, the first two residues relative to class I, although the N-terminus is acetylated like that for those enzymes. The chi subunit contains two more tryptophan residues than the class I subunits, accounting for the increased absorbance at 280 nm. There are also four additional acidic and two fewer basic side chains than in the class I beta structure, compatible with the markedly different electrophoretic mobility of the class III enzyme. Residue differences between class III and the other classes occur with nearly equal frequency in the coenzyme-binding and catalytic domains. The similarity in the number of exchanges relative to that of the enzymes of the other two classes supports conclusions that the three classes of alcohol dehydrogenase reflect stages in the development of separate enzymes with distinct functional roles. In spite of the many exchanges, the residues critical to basic functional properties are either completely unchanged--all zinc ligands and space-restricted Gly residues--or partly unchanged--residues at the coenzyme-binding pocket.(ABSTRACT TRUNCATED AT 250 WORDS)     

Structural relationships among class I isozymes of human liver alcohol dehydrogenase

The alpha subunit of human liver alcohol dehydrogenase has been submitted to structural analysis. Together with earlier work on the beta and gamma subunits, the results allow conclusions on the relationship of all known forms of the class I type of the enzyme. Two segments of the alpha subunit were determined; one was also reinvestigated in the beta and gamma subunits. The results establish 11 residue replacements among class I subunits in the segments analyzed and show that the alpha, beta, and gamma protein chains each are structurally distinct in the active site regions, where replacements affect positions influencing coenzyme binding (position 47; Gly in alpha, Arg in beta and gamma) and substrate specificity (position 48; Thr in alpha and beta, Ser in gamma). Residue 128, previously not detected in beta and gamma subunits, corresponds to a position of another isozyme difference (Arg in beta and gamma, Ser in alpha). The many amino acid replacements in alcohol dehydrogenases even at their active sites illustrate that in judgements of enzyme functions absolute importance of single residues should not be overemphasized. Available data suggest that alpha and gamma are the more dissimilar forms within the family of the three class I subunits that have resulted from two gene duplications. The class distinction of alcohol dehydrogenases previously suggested from enzymatic, electrophoretic, and immunological properties therefore also holds true in relation to their structures.     

Tissue- and species-specific expression patterns of class I,III, and IV Adh and Aldh1 mRNAs in rodent embryos

Alcohol and aldehyde dehydrogenases (ADHs and ALDHs) may be of interest in the pathology of Parkinson's disease (PD) because of their role in protection against toxins and in retinoid metabolism, which is required for growth and development of the mesencephalic dopamine system. In the present study, the spatial and temporal expression patterns of Adh1, Adh3, Adh4, and Aldh1 mRNAs in embryonic C57BL/6 mice (E9.5-E19.5) and Sprague-Dawley rats (E12.5-P0) have been investigated by using radioactive oligonucleotide in situ hybridization. High expression of Aldh1 mRNA was found in the developing mesencephalic dopamine neurons of both mice and rats. Expression of Adh1 and Adh4 mRNAs was observed in adrenal cortex and olfactory epithelium in mice. Additionally, Adh1 was expressed in epidermis, liver, conjunctival, and intestinal epithelium. In rat embryos, expression was less extensive, with Adh1 mRNA being found in liver and intestines. Adh3 expression was ubiquitous in both mouse and rat embryos, suggesting a housekeeping function of the gene. Consistent with previous studies in adult rats and mice, our data suggest that Adh3 is the only ADH class present in rodent brain. Adh and Aldh gene activity in mouse and rat embryos indicate the possible involvement of the respective enzymes in retinoid metabolism and participation in defense against toxic insults, including those that may be involved in the pathogenesis of PD. This work was supported by grants from the Swedish Research Council, the Swedish Parkinson Foundation, the Swedish Brain Foundation, Karolinska Institutet funds, AstraZeneca, and the US Public Health Service.     

In vitro dissociation and reassociation of human alcohol dehydrogenase class I isozymes

Freezing (-78 degrees C) and thawing (25 degrees C) a heterodimeric human alcohol dehydrogenase class I isozyme in the presence of 0.1 M sodium phosphate/0.1 mM DTT, pH 7.0, and the subsequent separation of the scrambled isozymes by HPLC are used to prepare homodimers from heterodimers, with recovery of enzyme activity ranging from 80 to 95%. The ratio of the three isozymes obtained from a heterodimer follows the binomial distribution of 1:2:1, indicating random reassociation of the two subunits. The physical and enzymatic properties of the reassociated isozymes are the same as those obtained directly from human liver preparations. The nature of subunit-subunit interactions of human ADH class I isozymes is examined by optimizing the conditions required for the formation of the new dimers "in vitro". The effect of a number of reagents previously used in the reversible dissociation of dehydrogenases is investigated. The coenzyme NAD+ is a potent inhibitor of the dissociation of dimers during the freeze/thaw procedure. The presence of sodium phosphate in the enzyme solution is essential during the freezing and thawing experiment. No appreciable dissociation/reassociation occurs in TES, HEPES, or even potassium phosphate. The reversible dissociation is due primarily to the decrease in pH because of the low solubility of Na2HPO4 at low temperatures. The reassociation occurs after thawing in a temperature-dependent process. There is no reactivation if the enzyme is incubated at 0 degrees C after thawing, while at 25 degrees C high recovery in activity is achieved in a time period ranging from 15 to 90 min.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunocytochemical and biochemical demonstration of formaldhyde dehydrogenase (class III alcohol dehydrogenase) in the nucleus.

Alcohol dehydrogenase (ADH), the major enzyme catalyzing the biological oxidation of ethanol in mammals, includes four classes with very different capacities for ethanol oxidation. Class III ADH is present in all the tissues and is well conserved throughout evolution. This enzyme has a low activity with ethanol, is specific for the glutathione-dependent oxidation of formaldehyde, and is therefore a formaldehyde dehydrogenase (FALDH). Until now there have been few and conflicting studies concerning its intracellular distribution, which is important for the understanding of its role in cell function. In the present work we used biochemical and immunocytochemical methods to assess the distribution of FALDH in rat hepatocytes and astroglial cells. With the glutathione-dependent formaldehyde dehydrogenase assay, we found the highest activity in the cytosol of hepatocytes and brain cells (12 and 2.6 mU/mg protein, respectively), but nuclei also exhibited significant activity (1.16 and 2.1 mU/mg protein, respectively). The immunocytochemical results showed the presence of FALDH binding sites in both the cytoplasm and the nucleus of the different cell types studied. Whereas no specific gold particle labeling was seen associated with any cytoplasmic component, in the nucleus the particles were found mainly over condensed chromatin and interchromatin regions. Finally, the gold particle density over both the nucleus and cytoplasm was greater in differentiated than in proliferating astrocytes in primary culture. In contrast, class I ADH, primarily responsible for ethanol metabolism, was found only in the cytoplasm of hepatocytes. We propose that one of the functions of FALDH is to protect cell structures, including DNA, from the toxic effects of endogenous formaldehyde, which is an intermediate in many metabolic process.     

Evidence for the identity of glutathione-dependent formaldehyde dehydrogenase and class III alcohol dehydrogenase

Formaldehyde dehydrogenase (EC 1.2.1.1) is a widely occurring enzyme which catalyzes the oxidation of S-hydroxymethylglutathione, formed from formaldehyde and glutathione, into S-formyglutathione in the presence of NAD. We determined the amino acid sequences for 5 tryptic peptides (containing altogether 57 amino acids) from electrophoretically homogeneous rat liver formaldehyde dehydrogenase and found that they all were exactly homologous to the sequence of rat liver class III alcohol dehydrogenase (ADH-2). Formaldehyde dehydrogenase was found to be able at high pH values to catalyze the NAD-dependent oxidation of long-chain aliphatic alcohols like n-octanol and 12-hydroxydodecanoate but ethanol was used only at very high substrate concentrations and pyrazole was not inhibitory. The amino acid sequence homology and identical structural and kinetic properties indicate that formaldehyde dehydrogenase and the mammalian class III alcohol dehydrogenases are identical enzymes.     

Distribution of laminin and types IV and III collagen in fetal,infant and adult human spleens

Summary The immunohistochemical distribution of the basement membrane (BM) proteins, laminin and type IV collagen, and interstitial type III collagen was investigated in 12 fetal spleens at the 15th–38th gestational weeks (g.w.) and in spleens of 8 infants from term to 4 years. The results were compared with the distribution of the same proteins in adult human spleen. BM proteins were found to be abundantly present in the red pulp of all spleens during the whole of development. The content of type III collagen gradually decreased with advancing age and, in adult spleen, there were only occasional positively staining fibers in Billroth's cords. This finding indicates that the composition of reticular fibers in the red pulp of spleen is different from the reticular fibers elsewhere in lymphoreticular tissue. Early signs of ring fiber formation in the walls of venous sinuses were detectable at the 15th–19th g.w., although their more complete development occurred relatively late from the 36th g.w. onwards. Ring fibers contained both laminin and type IV collagen in all the investigated spleens. They never stained for type III collagen. The developing white pulp was positive for BM proteins, but showed no staining for type III collagen at the 15th g.w. At later ages, the white pulp stained similarly for both BM proteins and type III collagen.     

Distribution of alcohol dehydrogenase mRNA in the rat central nervous system. Consequences for brain ethanol and retinoid metabolism.

The localization of alcohol dehydrogenase (ADH) in brain regions would demonstrate active ethanol metabolism in brain during alcohol consumption, which would be a new basis to explain the effects of ethanol in the central nervous system. Tissue sections from several regions of adult rat brain were examined by in situ hybridization to detect the expression of genes encoding ADH1 and ADH4, enzymes highly active with ethanol and retinol. ADH1 mRNA was found in the granular and Purkinje cell layers of cerebellum, in the pyramidal and granule cells of the hippocampal formation and in some cell types of cerebral cortex. ADH4 expression was detected in the Purkinje cells, in the pyramidal and granule cells of the hippocampal formation and in the pyramidal cells of cerebral cortex. High levels of ADH1 and ADH4 mRNAs were detected in the CNS epithelial and vascular tissues: leptomeninges, choroid plexus, ependymocytes of ventricle walls, and endothelium of brain vessels. Histochemical methods detected ADH activity in rodent cerebellar slices, while Western-blot analysis showed ADH4 protein in homogenates from several brain regions. In consequence, small but significant levels of ethanol metabolism can take place in distinct areas of the CNS following alcohol consumption, which could be related to brain damage caused by a local accumulation of acetaldehyde. Moreover, the involvement of ADH in the synthesis of retinoic acid suggests a role for the enzyme in the regulation of adult brain functions. The impairment of retinol oxidation by competitive inhibition of ADH in the presence of ethanol may be an additional origin of CNS abnormalities caused by ethanol.     

Molecular evolution of mammalian class I alcohol dehydrogenase

Phylogenetic relationship and the rates of evolution of mammalian alcohol dehydrogenases (ADHs) have been studied by using the amino acid sequences from the human (ADH alpha, ADH beta, and ADH gamma), rat, mouse, and horse (ADH E and ADH S). With the maize ADH1 and ADH2 used as references, the patterns of the amino acid replacements in the beta-sheets, alpha-helices, and random coils in each of the catalytic and coenzyme-binding domains were analyzed separately. The phylogenetic trees based on the different sets of amino acid substitutions consistently showed that (1) multiple ADHs in human and horse have arisen after mammalian radiation, (2) the common ancestor of human ADHs alpha and beta diverged from the ancestor of ADH gamma first and the former two ADHs diverged from each other more recently, and (3) the human ADHs are more closely related to the rodent ADHs than to the horse ADHs. Furthermore, the estimated branch lengths showed that the rodent ADHs are evolving faster than the other ADHs. This difference in evolutionary rate between the two groups of organisms is explainable either in terms of the difference in the number of cell generations per year or in terms of reduction of functional constraints.     

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)     

Rat liver alcohol dehydrogenase of class III. Primary structure, functional consequences and relationships to other alcohol dehydrogenases

The amino acid sequence of alcohol dehydrogenase of class III from rat liver (the enzyme ADH-2) has been determined. This type of structure is quite different from those of both the class I and the class II alcohol dehydrogenases. The rat class III structure differs from the rat and human class I structures by 133-138 residues (exact value depending on species and isozyme type); and from that of human class II by 132 residues. In contrast, the rat/human species difference within the class III enzymes is only 21 residues. The protein was carboxymethylated with iodo[2(14)C]acetate, and cleaved with CNBr and proteolytic enzymes. Peptides purified by exclusion chromatography and reverse-phase high-performance liquid chromatography were analyzed by degradation with a gas-phase sequencer and with the manual 4-N,N-dimethylaminoazobenzene-4'-isothiocyanate double-coupling method. The protein chain has 373 residues with a blocked N terminus. No evidence was obtained for heterogeneity. The rat ADH-2 enzyme of class III contains an insertion of Cys at position 60 in relation to the class I enzymes, while the latter alcohol dehydrogenase in rat (ADH-3) has another Cys insertion (at position 111) relative to ADH-2. The structure deduced explains the characteristic differences of the class III alcohol dehydrogenase in relation to the other classes of alcohol dehydrogenase, including a high absorbance, an anodic electrophoretic mobility and special kinetic properties. The main amino acid substitutions are found in the catalytic domain and in the subunit interacting segments of the coenzyme-binding domain, the latter explaining the lack of hybrid dimers between subunits of different classes. Several substitutions provide an enlarged and more hydrophilic substrate-binding pocket, which appears compatible with a higher water content in the pocket and hence could possibly explain the higher Km for all substrates as compared with the corresponding values for the class I enzymes. Finally the class III structure supports evolutionary relationships suggesting that the three classes constitute clearly separate enzymes within the group of mammalian zinc-containing alcohol dehydrogenases.     

Purification, characterization, and partial sequence of the glutathione-dependent formaldehyde dehydrogenase from Escherichia coli: a class III alcohol dehydrogenase.

The glutathione-dependent formaldehyde dehydrogenase from Escherichia coli has been purified to homogeneity and characterized. It is a 83,000-kDa homodimer containing 4 g-atom of zinc per dimer with a specific activity of 60 units/mg toward S-(hydroxymethyl)glutathione and NAD+ as substrates. Its isoelectric point, 4.4, is consistent with both its amino acid composition and chromatographic behavior on DEAE HPLC. The N-terminus is unblocked, and 47 residues from the N-terminus were sequenced. A computer search of the Swiss-Prot protein sequence data bank shows that the N-terminal sequence, [sequence; see text], is homologous with the mammalian class III alcohol dehydrogenases with 27 identities when compared to the human enzyme. Like the human, rat, and rabbit enzymes, it has high formaldehyde dehydrogenase activity in the presence of glutathione and catalyzes the oxidation of normal alcohols (ethanol, octanol, 12-hydroxydodecanoate) in a reaction that is not GSH-dependent. In addition, hemithiolacetals other than those formed from GSH, including omega-thiol fatty acids, also are substrates. The wide distribution and high degree of similarity of this enzyme to the plant and animal alcohol dehydrogenases suggest that the E. coli enzyme is closely related to the ancestor of the plant and animal dimeric zinc alcohol dehydrogenases.