Effects of ethanol administration on rat liver plasma membrane-bound enzymes.

Changes in the properties of rat liver plasma membranes were examined in studies designed to differentiate between direct and metabolic effects of acute and chronic ethanol ingestion. One hour after a single dose of ethanol (3 g/kg body weight) there were increases in Na+,K+-ATPase (32%) and 5'-nucleotidase (36%), and hepatic concentrations of ethanol and acetaldehyde were approximately 23 mM and 50 microM, respectively. Na+,K+-ATPase and 5'-nucleotidase activities in liver plasma membranes from control rats were not significantly changed by in vitro addition of 30 microM acetaldehyde or 50 mM ethanol. Increases in Na+,K+-ATPase (approximately 20%) and 5'-nucleotidase (approximately 30%) were also observed in liver plasma membranes isolated from rats 16 hr after feeding ethanol or sucrose supplements for 17 days. The intake of calories from dietary protein and lipid was decreased by about 25% in both the ethanol and sucrose-fed animals. Na+,K+-ATPase activities in liver plasma membranes isolated from control rats were inhibited (approximately 20%) by 100 mM ethanol in vitro, whereas no inhibition was observed using membrane preparations from rats fed ethanol or sucrose supplements. Our results show that changes in liver plasma membrane enzyme activities associated with a single dose of ethanol are not a direct effect correlated with blood, hepatic or plasma membrane concentrations of ethanol or acetaldehyde. Chronic ingestion of ethanol or sucrose supplements had similar effects on liver plasma membrane enzyme characteristics and parallel changes in nutrient intake may be a more feasible explanation of these results than any analogous direct effects of the two compounds.

A study of the oxidation of butan-1-ol and propan-2-ol by nicotinamide-adenine dinucleotide catalysed by yeast alcohol dehydrogenase.

1. The kinetics of oxidation of butan-1-ol and propan-2-ol by NAD+, catalysed by yeast alcohol dehydrogenase, were studied at 25 degrees C from pH 5.5 to 10, and at pH 7.05 from 14 degrees to 44 degrees C, 2. Under all conditions studied the results are consistent with a mechanism whereby some dissociation of coenzyme from the active enzyme-NAD+-alcohol ternary complexes occurs, and the mechanism is therefore not strictly compulsory order. 3. A primary 2H isotopic effect on the maximum rates of oxidation of [1-2H2]butan-1-ol and [2H7]propan-2-ol was found at 25 degrees C over the pH range 5.5-10. Further, in stopped-flow experiments at pH 7.05 and 25 degrees C, there was no transient formation of NADH in the oxidation of butan-1-ol and propan-2-ol. The principal rate-limiting step in the oxidation of dependence on pH of the maximum rates of oxidation of butan-1-ol and propan-2-ol is consisten with the possibility that histidine and cysteine residues may affect or control catalysis.

The role of an essential histidine residue of yeast alcohol dehydrogenase.

1. Inactivation of yeast alcohol dehydrogenase for diethyl pyrocarbonate indicates that one histidine residue per enzyme subunit is necessary for enzymic activity. The inactivated enzyme regains its activity over a period of days. 2. Enzyme modified by diethyl pyrocarbonate can form the binary enzyme - NADH complex with the same maximum NADH-binding capacity as that of native enzyme. Modified enzyme cannot form normal ternary complexes of the type enzyme - NADH - acetamide and enzyme - NAD+ - pyrazole, which are characteristic of native enzyme. 3. The rate constant for the reaction of enzyme with diethyl pyrocarbonate has been determined over the pH range 5.5--9. The histidine residue involved has approximately the same pKa as free histidine, but is 10-fold more reactive than free histidine.

A study of the pH- and temperature-dependence of the reactions of yeast alcohol dehydrogenase with ethanol, acetaldehyde and butyraldehyde as substrates.

The kinetics of ethanol oxidation by NAD+, and acetaldehyde and butyraldehyde reduction by NADH, catalysed by yeast alcohol dehydrogenase, were studied in the pH range 4.9--9.9 at 25 degrees C and in the temperature range 14.8--43.5 degrees C at pH 7.05. The kinetics of reduction of acetaldehyde by [4A-2H]NADH at pH 7.05 and pH 8.9 at 25 degrees C were also studied. The results of the kinetic experiments indicate that the mechanism of catalysis, previously proposed on the basis of studies at pH 7.05 and 25 degrees C (Dickinson & Monger, 1973), applies over the wide range of conditions now tested. Values of some of the initial-rate parameters obtained were used to deduce information about the pH- and temperature-dependence of the specific rates of combination of enzyme and coenzymes and of the dissociation of the enzyme--coenzyme compounds. Primary and secondary plots of initial-rate data are deposited as Supplementary Publication SUP 50043 (20 pages) with the British Library (Lending Division), Boston Spa, Wetherby, Yorks. LS23 7BQ, U.K., from whom copies may be obtained under the terms indicated in Biochem. J. (1975) 145, 5.

Inhibition by ethanol, acetaldehyde and trifluoroethanol of reactions catalysed by yeast and horse liver alcohol dehydrogenases.

1. Produced inhibition by ethanol of the acetaldehyde-NADH reaction, catalysed by the alcohol dehydrogenases from yeast and horse liver, was studied at 25 degrees C and pH 6-9. 2. The results with yeast alcohol dehydrogenase are generally consistent with the preferred-pathway mechanism proposed previously [Dickenson & Dickinson (1975) Biochem. J. 147, 303-311]. The observed hyperbolic inhibition by ethanol of the maximum rate of acetaldehyde reduction confirms the existence of the alternative pathway involving an enzyme-ethanol complex. 3. The maximum rate of acetaldehyde reduction with horse liver alcohol dehydrogenase is also subject to hyperbolic inhibition by ethanol. 4. The measured inhibition constants for ethanol provide some of the information required in the determination of the dissociation constant for ethanol from the active ternary complex. 5. Product inhibition by acetaldehyde of the ethanol-NAD+ reaction with yeast alcohol dehydrogenase was examined briefly. The results are consistent with the proposed mechanism. However, the nature of the inhibition of the maximum rate cannot be determined within the accessible range of experimental conditions. 6. Inhibition of yeast alcohol dehydrogenase by trifluoroethanol was studied at 25 degrees C and pH 6-10. The inhibition was competitive with respect to ethanol in the ethanol-NAD+ reaction. Estimates were made of the dissociation constant for trifluoroethanol from the enzyme-NAD+-trifluoroethanol complex in the range pH6-10.

Estimation of rate and dissociation constants involving ternary complexes in reactions catalysed by yeast alcohol dehydrogenase.

Stopped-flow studies of oxidation of butan-1-ol and propan-2-ol by NAD(+) in the presence of Phenol Red and large concentrations of yeast alcohol dehydrogenase give no evidence for the participation of a group of pK(a) approx. 7.6 in alcohol binding. Such a group has been implicated in ethanol binding to horse liver alcohol dehydrogenase [Shore, Gutfreund, Brooks, Santiago & Santiago (1974) Biochemistry13, 4185-4190]. The present result supports previous findings based on steady-state kinetic studies with the yeast enzyme. Stopped-flow studies of the yeast alcohol dehydrogenase-catalysed reduction of acetaldehyde by NADH in the presence of ethanol as product inhibitor indicate that the rate-limiting step is NAD(+) release from the enzyme-NAD(+)-ethanol product complex. This finding permits calculation of K(3), the dissociation constant for ethanol from the enzyme-NAD(+)-ethanol complex, by using the product-inhibition data of Dickenson & Dickinson (1978) (Biochem. J.171, 613-627). The calculations show that K(3) varies very little with pH in the range 5.95-8.9, and this agrees with the findings of the stopped-flow experiments described above. Absorption and fluorescence measurements on mixtures of substrates and coenzymes in the presence of high concentrations of alcohol dehydrogenase have been used to estimate values for the ratio [enzyme-NADH-acetaldehyde]/ [enzyme-NAD(+)-ethanol] at equilibrium. The values obtained were in the range 0.11+/-0.04, and this value together with estimates of K(3) was used to provide estimates of values for rate constants and dissociation constants for steps within the catalytic mechanism.

A study of the ionic properties of the essential histidine residue of yeast alcohol dehydrogenase in complexes of the enzyme with its coenzymes and substrates.

1. Initial-rate studies of the reduction of acetaldehyde by NADH, catalysed by yeast alcohol dehydrogenase, were performed at pH 4.9 and 9.9, in various buffers, at 25 degrees C. The results are discussed in terms of the mechanism previously proposed for the pH range 5.9-8.9 [Dickenson & Dickinson (1975) Biochem. J. 147, 303-311]. 2. Acetaldehyde forms a u.v.-absorbing complex with glycine. This was shown not to affect the results of kinetic experiments under the conditions used in this and earlier work. 3. The variation with pH of the dissociation constant for the enzyme-NADH complex, calculated from the initial-rate data, indicates that the enzyme possesses a group with pK7.1 in the free enzyme and pK8.7 in the complex. 4. The pH-dependences of the second-order rate constants for inactivation of the enzyme by diethyl pyrocarbonate were determined for the free enzymes (pK7.1), the enzyme-NAD+ complex (pK approx. 7.1) and the enzyme-NADH complex (pK approx. 8.4). The essential histidine residue may therefore be the group involved in formation and dissociation of the enzyme-NADH complex. 5. Estimates of the rate constant for reaction of acetaldehyde with the enzyme-NADH complex indicate that acetaldehyde may combine only when the essential histidine residue is protonated. The dissociation constants for butan-1-ol and propan-2-ol, calculated on the basis of earlier kinetic data, are, however, independent of pH. 6. The results obtained are discussed in relation to the role of the essential histidine residue in the mechanism of formation of binary and ternary complexes of the enzyme with its coenzymes and substrates.

Some properties of an alcohol dehydrogenase partially purified from baker's yeast grown without added zinc.

Alcohol dehydrogenase was partially purified from yeast (Saccharomyces cerevisiae) grown in the presence of 20 muM-MnSO4 without added Zn2+ and from yeast grown in the presence of 1.8 muM-MnSO4. The enzyme from yeast grown with added Zn2+ has the same properties as the crystalline enzyme from commercial supplies of baker's yeast. The enzyme from yeast grown without added An2+ has quite different properties. It has a mol.wt. in the region of 72000 and an S 20 w of 5.8S. The values can be compared with a mol.wt. of 141000 and an S 20 w of 7.6S for the crystalline enzyme. ADP-ribose, a common impurity in commercial samples of NAD+, is a potent competitive inhibitor of the new enzyme (K1 = 0.5 muM), but is not so for the crystalline enzyme. The observed maximum rate of ethanol oxidation at pH 7.05 and 25 degrees C was decreased 12-fold by the presence of 0.06 mol of inhibitor/mol of NAD+ when using the enzyme from Zn2+-deficient yeast, but with crystalline enzyme the maximum rate was essentially unchanged by this concentration of inhibitor. The kinetic characteristics for the two enzymes with ethanol, butan-1-ol, acetaldehyde and butyraldehyde as substrates are markedly different. These kinetic differences are discussed in relation to the mechanism of catalysis for the enzyme from Zn2+-deficient yeast.

Blood concentrations of acetaldehyde during chlorpropamide-alcohol flush.

To test the suggestion that chlorpropamide-alcohol flushing (CPAF) resembles the disulfiram effect and might be mediated by acetaldehyde, the initial metabolite of alcohol, blood concentrations of acetaldehyde were measured after a drink of alcohol in controls and diabetics positive and negative for CPAF. The CPAF-positive diabetics had significantly greater blood acetaldehyde concentrations after alcohol than the CPAF-negative diabetics both with a single dose of chlorpropamide and after two weeks' chlorpropamide treatment. Concentrations in the CPAF-positive group after chlorpropamide were also significantly greater than after a placebo tablet. There was also a clear separation in the increase in facial temperature after two weeks of chlorpropamide between the CPAF-positive and CPAF-negative groups (although there was some overlap after a single tablet). There was no difference in plasma chlorpropamide or alcohol concentrations between CPAF-positive and CPAF-negative diabetics. These findings show that CPAF is distinct from alcohol flushing and that the acetaldehyde concentration in the blood provides an objective measure of CPAF. The difference between flushing and non-flushing diabetics cannot be accounted for by differences in blood concentrations of chlorpropamide or alcohol.