Mammalian liver alcohol dehydrogenases

Phytophenols in whisky lower blood acetaldehyde level by depressing alcohol metabolism through inhibition of alcohol dehydrogenase 1 (class I) in mice

We recently reported that the maturation of whisky prolongs the exposure of the body to a given dose of alcohol by reducing the rate of alcohol metabolism and thus lowers the blood acetaldehyde level (Alcohol Clin Exp Res. 2007;31:77s-82s). In this study, administration of the nonvolatile fraction of whisky was found to lower the concentration of acetaldehyde in the blood of mice by depressing alcohol metabolism through the inhibition of liver alcohol dehydrogenase (ADH). Four of the 12 phenolic compounds detected in the nonvolatile fraction (caffeic acid, vanillin, syringaldehyde, ellagic acid), the amounts of which increase during the maturation of whisky, were found to strongly inhibit mouse ADH 1 (class I). Their inhibition constant values for ADH 1 were 0.08, 7.9, 15.6, and 22.0 mumol/L, respectively, whereas that for pyrazole, a well-known ADH inhibitor, was 5.1 mumol/L. The 2 phenolic aldehydes and ellagic acid exhibited a mixed type of inhibition, whereas caffeic acid showed the competitive type. When individually administered to mice together with ethanol, each of these phytophenols depressed the elimination of ethanol, thereby lowering the acetaldehyde concentration of blood. Thus, it was demonstrated that the enhanced inhibition of liver ADH 1 due to the increased amounts of these phytophenols in mature whisky caused the depression of alcohol metabolism and a consequent lowering of blood acetaldehyde level. These substances are commonly found in various food plants and act as antioxidants and/or anticarcinogens. Therefore, the intake of foods rich in them together with alcohol may not only diminish the metabolic toxicity of alcohol by reducing both the blood acetaldehyde level and oxidative stress, but also help limit the amount of alcohol a person drinks by depressing alcohol metabolism.

Toc12, a novel subunit of the intermembrane space preprotein translocon of chloroplasts

Translocation of proteins across membranes is essential for the biogenesis of each cell and is achieved by proteinaceous complexes. We analyzed the translocation complex of the intermembrane space from chloroplasts and identified a 12-kDa protein associated with the Toc machinery. Toc12 is an outer envelope protein exposing a soluble domain into the intermembrane space. Toc12 contains a J-domain and stimulates the ATPase activity of DnaK. The conformational stability and the ability to stimulate Hsp70 are dependent on a disulfide bridge within the loop region of the J-domain, suggesting a redox-regulated activation of the chaperone. Toc12 is associated with Toc64 and Tic22. Its J-domain recruits the Hsp70 of outer envelope membrane to the intermembrane space translocon and facilitates its interaction to the preprotein.

In vitro co-metabolism of ethanol and cyclic ketones

The paper presents the results of studies concerning the effects of four cyclic ketones, i.e. cyclopentanone (Pen), cyclohexanone (Hex), cycloheptanone (Hep) and cyclooctanone (Oct) on metabolism of ethanol (EtOH) in vitro. The fraction S9 (supernatant with the removed mitochondria) was used obtained from homogenized rat livers. An increase in reduced nicotinamide adenine dinucleotide (NADH) was examined spectrophotometrically (at 340 nm) while the substrate disappearance and metabolite increase were determined using head-space gas chromatography. The addition of cyclic ketones statistically significantly affected a decrease in the A(340) level, particularly during co-metabolism of EtOH and Hex. The EtOH loss was significantly higher (than the loss observed during metabolism of EtOH alone) only in EtOH-Hex and EtOH-Hep systems, which may be explained by the fact that reoxidation of NADH to NAD+ is quicker in these systems than dissociation of the alcohol dehydrogenase (ADH)-NADH complex.

Oxidation and nitrosation in the nitrogen monoxide/superoxide system

Based on the previous report of McCord and co-workers (Crow, J. P., Beckman, J. S., and McCord, J. M. (1995) Biochemistry 34, 3544-3552), the zinc dithiolate active site of alcohol dehydrogenase (ADH) has been studied as a target for cellular oxidants. In the nitrogen monoxide ((*NO)/superoxide (O(2)) system, an equimolar generation of both radicals under peroxynitrite (PN) formation led to rapid inactivation of ADH activity, whereas hydrogen peroxide and ( small middle dot)NO alone reacted too slowly to be of physiological significance. 3-Morpholino sydnonimine inactivated the enzyme with an IC(50) value of 250 nm; the corresponding values for PN, hydrogen peroxide, and (*NO) were 500 nm, 50 microm, and 200 microm. When superoxide was generated at low fluxes by xanthine oxidase, it was quite effective in ADH inactivation (IC(50) (XO) approximately 1 milliunit/ml). All inactivations were accompanied by zinc release and disulfide formation, although no strict correlation was observed. From the two zinc thiolate centers, only the zinc Cys(2)His center released the metal by oxidants. The zinc Cys(4) center was also oxidized, but no second zinc atom could be found with 4-(2-pyridylazo)resorcinol (PAR) as a chelating agent except under denaturing conditions. Surprisingly, the oxidative actions of PN were abolished by a 2-3-fold excess of (*)NO under generation of a nitrosating species, probably dinitrogen trioxide. We conclude that in cellular systems, low fluxes of (*)NO and O(2) generate peroxynitrite at levels effective for zinc thiolate oxidations, facilitated by the nucleophilic nature of the complexed thiolate group. With an excess of (*)NO, the PN actions are blocked, which may explain the antioxidant properties of (*)NO and the mechanism of cellular S-nitrosations.

Overexpression, purification, and characterization of S-adenosylhomocysteine hydrolase from Leishmania donovani

The gene encoding S-adenosylhomocysteine (AdoHcy) hydrolase in Leishmania donovani was subcloned into an expression vector (pPROK-1) and expressed in Escherichia coli. Recombinant L. donovani AdoHcy hydrolase was then purified from cell-free extracts of E. coli using three chromatographic steps (DEAE-cellulose chromatofocusing, Sephacryl S-300 gel filtration, and Q-Sepharose ion exchange). The purified recombinant L. donovani enzyme exists as a tetramer with a molecular weight of approximately 48 kDa for each subunit. Unlike recombinant human AdoHcy hydrolase, the catalytic activity of the recombinant L. donovani enzyme was shown to be dependent on the concentration of NAD+ in the incubation medium. The dissociation constant (Kd) for NAD+ with the L. donovani enzyme was estimated to be 2.1 +/- 0.2 microM. The Km values for the natural substrates of the enzyme, AdoHcy, Ado, and Hcy, were determined to be 21 +/- 3, 8 +/- 2, and 82 +/- 5 microM, respectively. Several nucleosides and carbocyclic nucleosides were tested for their inhibitory effects on this parasitic enzyme, and the results suggested that L. donovani AdoHcy hydrolase has structural requirements for binding inhibitors different than those of the human enzyme. Thus, it may be possible to eventually exploit these differences to design specific inhibitors of this parasitic enzyme as potential antiparasitic agents.

Inhibition of canine and feline alcohol dehydrogenase activity by fomepizole

OBJECTIVE

To determine and compare substrate specificity and kinetic rate constants of feline and canine alcohol dehydrogenase (ADH) with ethanol (EtOH) and ethylene glycol (EG) as substrates in vitro, with and without fomepizole.

SAMPLE POPULATION

Livers from 3 dogs and 3 cats.

PROCEDURE

Canine and feline ADH activity, in cytosolic fractions of homogenized liver, was determined by use of various concentrations of nicotinamide adenine dinucleotide (NAD), EtOH, or EG as substrates. Initial reaction velocities were calculated, and kinetic inhibition rate constants (Ki) for fomepizole were determined.

RESULTS

Substrate specificity of canine and feline ADH for EtOH or EG was not significantly different. A 2-fold difference was detected in the maximal velocity of canine, compared with feline, ADH, using either substrate. Fomepizole Ki in feline hepatic homogenates was significantly greater than Ki in canine hepatic homogenates when either EtOH or EG was used as substrate (10- and 30-fold, respectively). A 6-fold increase in the concentration of fomepizole was required to achieve ADH inhibition, with feline homogenates equivalent to those of canine homogenates.

CONCLUSIONS AND CLINICAL RELEVANCE

Feline ADH has lower enzymatic capacity for turnover or is less concentrated in liver than canine ADH with regard to EtOH and EG catalysis. Canine ADH was more effectively inhibited by fomepizole than feline ADH. Results suggest that higher dosages of fomepizole may be more effective to treat cats with EG intoxication than dosages reported to treat dogs.

Hydroperoxidic inhibitor of horse liver alcohol dehydrogenase activity, tightly bound to the enzyme-NAD+ complex, characteristically degrades the coenzyme

The strong inhibition of horse liver alcohol dehydrogenase (HLAD) by p-methylbenzyl hydroperoxide (XyHP) is only transient, XyHP behaves also as a pseudo-substrate of the enzyme and in the presence of NAD+, is degraded by HLAD to (as yet unidentified) non-inhibiting products while the NAD+ is converted to a derivative similar to the "NADX", originally observed in an analogous reaction of HLAD with hydrogen peroxide. The apparent KM for XyHP is approximately 10(4) times smaller than that for H2O2. The catalytic constant kcat for HLAD degradation of XyHP is two orders of magnitude less than that for ethanol dehydrogenation. XyHP inhibits both directions of the alcohol-aldehyde interconversion with equal potency. The first step of the inhibition mechanism is a tight binding of XyHP to the binary HLAD-NAD+ complex.

Alcohol dehydrogenase isozymes in baboons: tissue distribution, catalytic properties, and variant phenotypes in liver, kidney, stomach, and testis

Isoelectric focusing and cellulose acetate electrophoresis were used to examine the multiplicity, tissue distribution, and variability of alcohol dehydrogenase (ADH) among baboons, a primate species used as a model for research on alcohol metabolism and alcohol-induced liver pathology. Five major ADH isozymes were resolved and distinguished on the basis of their isoelectric points, tissue distributions, relative activities with alcohol substrates, and sensitivities to inhibition with 4-methyl pyrazole. ADH-1 and ADH-2 exhibited class I kinetic properties and were observed in high activity in kidney and liver extracts, respectively. ADH-3 showed class II kinetic properties, exhibiting high activity in stomach extracts, and was widely distributed in extracts of other baboon tissues, including kidney, esophagus, heart, testis, brain, and male sex accessory tissues. ADH-4 also showed class II ADH properties but was found only in liver (similar to human "pi-ADH"). ADH-5 exhibited class III ADH kinetic properties, being inactive with ethanol up to 0.5 M (similar to human "chi-ADH") and was distributed widely in baboon tissue extracts. Major activity variation was observed for liver ADH-4 between different animals. An electrophoretic variant for ADH-3 was observed for the enzyme in stomach, kidney, and testis extracts, and activity variation existed for this isozyme in kidney extracts. It is apparent that baboon ADH shares a number of features with the human ADH phenotype; however, several species-specific differences were observed, particularly for the liver and kidney class I isozymes and for stomach ADH.

Alcohol dehydrogenase activity and isoenzyme distribution in the organs of cow, pig and sheep

The highest specific activities and the most complex isoenzyme patterns were found in livers of these species, characteristic isoenzymes were observed also in the core of adrenal glands. In spite of a general resemblance the isoenzyme patterns of liver alcohol dehydrogenase are specific for the species tested; the activities in most organs (and blood sera) increase in the sequence cow, pig and sheep. The activities in foetal bovine organs are substantially lower than those in organs of adult cows, the most pronounced increase in activities during the intrauteral development was observed in liver.

The polymorphisms of alcohol and aldehyde dehydrogenase and their significance for acetaldehyde toxicity

Evidence is growing that acetaldehyde is responsible for some toxic effects after ethanol intake. Large individual and racial differences in blood and breath acetaldehyde concentrations are observed after alcohol consumption. In many Orientals but few Caucasians extremely high blood acetaldehyde levels occur leading to an acute aldehyde syndrome also observed after treatment with aldehyde dehydrogenase inhibitors. Individuals suffering from the aversive symptoms of that syndrome will be protected from excessive drinking and the related problems. In chronic aldehydism slightly elevated aldehyde concentrations are observed possibly leading to organic injury due to the cytotoxic action of acetaldehyde. Sites exhibiting high alcohol dehydrogenase activity may specifically be affected in alcoholics.

Hypothesis: metabolic activity of the colonic bacteria influences organ injury from ethanol

Incubation of human fecal homogenates with ethanol (0.078 gm per dl) resulted in accumulation of increased quantities of higher alcohols and other unidentified metabolites when compared with homogenates incubated without ethanol. Studies in rats demonstrated nearly perfect equilibration between blood and colonic luminal ethanol suggesting that the colonic flora in alcoholics is chronically exposed to ethanol concentrations in the range used in the homogenate experiments. The higher alcohols produced by the homogenates were rapidly absorbed from the colon. We hypothesize that, when exposed to ethanol, the colonic flora produced toxic compounds which are absorbed and influence the body's response to ingested ethanol. Individual differences in this bacterial metabolism may account for the wide individual differences in susceptibility to ethanol-related organ injury.

Metabolism of tiaramide in vitro. II. Oxidation of piperazineethanol group in tiaramide by 105 000 g supernatants from monkey and rat liver

1. The piperazineethanol group in tiaramide was metabolized to the corresponding piperazineacetic acid group by monkey- and rat-liver preparations. 2. Formation of the piperazineacetic acid by soluble fractions from monkey and rat livers was faster with NAD+ than with NADP+ and was inhibited by pyrazole and disulfiram. 3. Tiaramide treatment did not impair ethanol elimination from blood of rats, but pyrazole pretreatment caused a drastic decrease of the piperazineacetic acid metabolite in the liver and serum of rats treated with tiaramide. 4. These results, and studies on partially purified liver enzymes, indicate that in monkey and rat liver, oxidation of the piperazineethanol moiety in tiaramide to piperazineacetic acid is catalysed by alcohol and aldehyde dehydrogenase.

Genetic regulation and development of alcohol dehydrogenases in the mouse

Alcohol dehydrogenase (ADH) of mouse tissues was investigated using electrophoretic zymogram methods. ADH activity is widely distributed in mouse tissues and exists as at least two genetic isozymes, designated A2 and C2, which are predominantly localised in liver and stomach respectively. Electrophoretic and activity variants of ADH-C2 among inbred strains of mice have been used to localise the gene encoding this enzyme (Adh-3) and a closely linked temporal locus (Adh-3-t) on chromosome 3 of this organism. Recent developmental studies on ADH isozymes in the mouse have been reviewed.

Genetics and ontogeny of alcohol dehydrogenase isozymes in the mouse: evidence for a cis-acting regulator gene (Adt-i) controlling C2 isozyme expression in reproductive tissues and close linkage of Adh-3 and Adt-i on chromosome 3

An electrophoretic variant previously reported for the stomach isozyme of alcohol dehydrogenase (ADH-C2) in inbred strains of Mus musculus (Holmes, 1977) has been used to localize the gene encoding this enzyme (Adh-3) on chromosome 3 near Va (varitint) (9.6 +/- 3.6% recombinants). Genetic variation of ADH-C2 activity in male and female reproductive tissues among inbred strains and Harwell linkage testing stocks was also observed. Reproductive tissue ADH-C2 phenotypes were inherited in a normal Mendelian fashion among F2 progeny of an F1 (LII x C57BL/Go) x C57BL/Go backcross as though controlled by a single cis-acting regulator locus (designated Adt-1) with two alleles: Adt-1a (presence of ADH-C2) and Adt-1b (absence or low activity of ADH-C2). No recombinants were observed among 73 progeny or among 13 inbred strains and six Harwell linkage testing stocks of mice, indicating that Adh-3 and Adt-1 are closely linked or identical genes. A single recombinant phenotype was observed in Peru-Coppock mice, suggesting that they are separate genes. Ontogenetic analyses demonstrated that ADH-B2 is present throughout development from late fetal stages in stomach, liver, and kidney; similar results were found for ADH-C2 in developing kidney and stomach extracts, whereas ADH-A2 exhibited high activity in liver extracts after 3 weeks of age in both sexes and in male kidney extracts after 6 weeks.

Electrophoretic analyses of alcohol dehydrogenase, aldehyde dehydrogenase, aldehyde oxidase, sorbitol dehydrogenase and xanthine oxidase from mouse tissues

1. Cellulose acetate zymograms of alcohol dehydrogenase (ADH), aldehyde dehydrogenase, sorbitol dehydrogenase, aldehyde oxidase, "phenazine" oxidase and xanthine oxidase extracted from tissues of inbred mice were examined. 2. ADH isozymes were differentially distributed in mouse tissues: A2--liver, kidney, adrenals and intestine; B2--all tissues examined; C2--stomach, adrenals, epididymis, ovary, uterus, lung. 3. Two NAD+-specific aldehyde dehydrogenase isozymes were observed in liver and kidney and differentially distributed in other tissues. Alcohol dehydrogenase, aldehyde oxidase, "phenazine" oxidase and xanthine oxidase were also stained when aldehyde dehydrogenase was being examined. 4. Two aldehyde oxidase isozymes exhibited highest activities in liver. 5. "Phenazine oxidase" was widely distributed in mouse tissues whereas xanthine oxidase exhibited highest activity in intestine and liver extracts. 6. Genetic variants for ADH-C2 established its identity with a second form of sorbitol dehydrogenase observed in stomach and other tissues. The major sorbitol dehydrogenase was found in high activity in liver, kidney, pancreas and male reproductive tissues.

Kinetics of native and activated isozymes of horse liver alcohol dehydrogenase

The major isozymes of horse liver alcohol dehydrogenase (EC 1.1.1.1), EE, ES, and SS, have been separated by chromatography on phosphocellulose. Product inhibition studies showed that the kinetic behavior of EE and SS isozymes was consistent with the ordered BiBi mechanism. The different primary structures of the E and S subunits were expressed with higher Michaelis constants for ethanol and acetaldehyde and lower activity for the SS isozyme when compared with the EE isozyme. The differences for SS isozyme are reflections of slower rates of association and dissociation of coenzymes and slower rates of hydrogen transfer, not of affinities for the substrates. The contributions of each subunit in ES isozyme to the kinetic constants were not additive, indicating that the subunits may not act independently. Activation of the isozymes by amidination and alkylation suggested that lysine residues were present at the active sites of both E and S subunits. Kinetic studies indicated that isonicotinimidylation increased enzyme activity of the three isozymes by increasing the rates of dissociation of the enzyme-coenzyme complexes.