scholarly journals Hydrogen transfer between ethanol molecules during oxidoreduction in vivo

1985 ◽  
Vol 229 (2) ◽  
pp. 315-322 ◽  
Author(s):  
T Cronholm
Keyword(s):  
Alcohol Dehydrogenase ◽  
Isotope Effect ◽  
Hydrogen Transfer ◽  
Ethanol Oxidation ◽  
Internal Standard ◽  
Ethanol Metabolism ◽  
Acetaldehyde Oxidation ◽  
Extensive Formation ◽  
Rate Limiting

Rates of exchange catalysed by alcohol dehydrogenase were determined in vivo in order to find rate-limiting steps in ethanol metabolism. Mixtures of [1,1-2H2]- and [2,2,2-2H3]ethanol were injected in rats with bile fistulas. The concentrations in bile of ethanols having different numbers of 2H atoms were determined by g.l.c.-m.s. after the addition of [2H6]ethanol as internal standard and formation of the 3,5-dinitrobenzoates. Extensive formation of [2H4]ethanol indicated that acetaldehyde formed from [2,2,2-2H3]ethanol was reduced to ethanol and that NADH used in this reduction was partly derived from oxidation of [1,1-2H2]ethanol. The rate of acetaldehyde reduction, the degree of labelling of bound NADH and the isotope effect on ethanol oxidation were calculated by fitting models to the found concentrations of ethanols labelled with 1-42H atoms. Control experiments with only [2,2,2-2H3]ethanol showed that there was no loss of the C-2 hydrogens by exchange. The isotope effect on ethanol oxidation appeared to be about 3. Experiments with (1S)-[1-2H]- and [2,2,2-2H3]ethanol indicated that the isotope effect on acetaldehyde oxidation was much smaller. The results indicated that both the rate of reduction of acetaldehyde and the rate of association of NADH with alcohol dehydrogenase were nearly as high as or higher than the net ethanol oxidation. Thus, the rate of ethanol oxidation in vivo is determined by the rates of acetaldehyde oxidation, the rate of dissociation of NADH from alcohol dehydrogenase, and by the rate of reoxidation of cytosolic NADH. In cyanamide-treated rats, the elimination of ethanol was slow but the rates in the oxidoreduction were high, indicating more complete rate-limitation by the oxidation of acetaldehyde.

Regulation of ethanol metabolism in the rat

1987 ◽  
Vol 65 (5) ◽  
pp. 458-466 ◽  
Author(s):  
S. Cheema-Dhadli ◽  
F. A. Halperin ◽  
K. Sonnenberg ◽  
V. MacMillan ◽  
M. L. Halperin
Keyword(s):  
Alcohol Dehydrogenase ◽  
Ethanol Oxidation ◽  
Maximum Velocity ◽  
Reducing Power ◽  
Ammonium Bicarbonate ◽  
Ethanol Metabolism ◽  
Urea Synthesis ◽  
Major Pathway ◽  
Nadh Generation

The purpose of these experiments was to examine the factors which regulate ethanol metabolism in vivo. Since the major pathway for ethanol removal requires flux through hepatic alcohol dehydrogenase, the activity of this enzyme was measured and found to be 2.9 μmol/(min∙g liver). Ethanol disappearance was linear for over 120 min in vivo and the blood ethanol fell 0.1 mM/min; this is equivalent to removing 20 μmol ethanol/min and would require that flux through alcohol dehydrogenase be about 60% of its measured maximum velocity. To test whether ethanol metabolism was limited by the rate of removal of one of the end products (NADH) of alcohol dehydrogenase, fluoropyruvate was infused to reoxidize hepatic NADH and to prevent NADH generation via flux through pyruvate dehydrogenase. There was no change in the rate of ethanol clearance when fluoropyruvate was metabolized. Furthermore, enhancing endogenous hepatic NADH oxidation by increasing the rate of urea synthesis (converting ammonium bicarbonate to urea) did not augment the steady-state rate of ethanol oxidation. Hence, transport of cytoplasmic reducing power from NADH into the mitochondria was not rate limiting for ethanol oxidation. In contrast, ethanol oxidation at the earliest time periods could be augmented by increasing hepatic urea synthesis.

scholarly journals ВПЛИВ ЗАМІЩЕННОГО НІКОТИНАМІДУ ТА ЙОГО МОЖЛИВИХ МЕТАБОЛІТІВ НА АКТИВНІСТЬ ФЕРМЕНТІВ ОБМІНУ ЕТАНОЛУ

2020 ◽  
Vol 144 (2) ◽  
pp. 98-104
Author(s):  
О. В. Кислова
Keyword(s):  
Alcohol Dehydrogenase ◽  
Aldehyde Dehydrogenase ◽  
Ethanol Oxidation ◽  
The Body ◽  
Inhibition Constant ◽  
Ethanol Metabolism ◽  
Dehydrogenase Reaction ◽  
Metabolism Enzymes

To study the influence of N-phenyl-N-(1-cyclopropylethyl)nicotinamide and its possible metabolites: hydrochlorides of N-(1-cyclopropylethyl)amine and N-phenyl-N-(1-cyclopropylethyl)amine - on the activity of  main ethanol oxidation enzymes in vitro and kinetic nature of their interaction. The studies were carried out using alcohol dehydrogenase and aldehyde dehydrogenase of rat liver subcellular fractions, which were obtained by differential centrifugation. The enzyme activity was determined spectrophotometrically. The kinetic nature of alcohol dehydrogenase and isozyme form of aldehyde dehydrogenase  interaction with substituted nicotinamide was investigated in the concentration range of 25-100 μM. The research results were processed by the Lineweaver-Burk method. Studies have shown that N-phenyl-N-(1-cyclopropylethyl)nicotinamide is able to reduce the rate of the reverse alcohol dehydrogenase reaction of acetaldehyde reduction to ethanol in the presence of NADH by 46% with an inhibition constant 53 μM. The activity of soluble mitochondrial aldehyde dehydrogenase was suppressed by 50% with an inhibition constant 108 μM. The kinetic nature of the substituted nicotinamide interaction with enzymes at saturating concentrations of the reaction cofactors NADH and NAD+ is quite complex. Allosteric effects can play a significant role in enzymatic activity. Possible metabolites of the compound - hydrochlorides of N-(1-cyclopropylethyl)- and N-phenyl-N-(1-cyclopropylethyl)amine – didn`t significantly influence on ethanol metabolism enzymes activity. A new inhibitor of the rate of the reverse alcohol dehydrogenase reaction and the activity of soluble mitochondrial isozyme form of aldehyde dehydrogenase, which lead to the accumulation of acetaldehyde in the body, has been discovered. N-phenyl-N-(1-cyclopropylethyl)nicotinamide can be used as a potential antialcohol sensitizing drug after research in vivo.

Ethanol Metabolism in Vivo and the Role of Hepatic Microsomal Ethanol Oxidation

1972 ◽  
Vol 33 (3) ◽  
pp. 751-755 ◽  
Author(s):  
Mary K. Roach ◽  
Myrna Khan ◽  
Marguerite Knapp ◽  
W. N. Reese
Keyword(s):  
Ethanol Oxidation ◽  
Ethanol Metabolism

Ethanol metabolism in vivo by the microsomal ethanol-oxidizing system in deermice lacking alcohol dehydrogenase (ADH)

1984 ◽  
Vol 33 (5) ◽  
pp. 807-814 ◽  
Author(s):  
Yohsuke Shigeta ◽  
Fumio Nomura ◽  
Shinji Iida ◽  
Maria A. Leo ◽  
Michael R. Felder ◽  
...  
Keyword(s):  
Alcohol Dehydrogenase ◽  
Ethanol Metabolism

scholarly journals A study of the kinetics and mechanism of yeast alcohol dehydrogenase with a variety of substrates

1973 ◽  
Vol 131 (2) ◽  
pp. 261-270 ◽  
Author(s):  
F. M. Dickinson ◽  
G. P. Monger
Keyword(s):  
Alcohol Dehydrogenase ◽  
Ethanol Oxidation ◽  
Ternary Complexes ◽  
Kinetics Of Oxidation ◽  
Yeast Alcohol Dehydrogenase ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Binary Complexes ◽  
Rate Limiting ◽  
Kinetics Of

1. The kinetics of oxidation of ethanol, propan-1-ol, butan-1-ol and propan-2-ol by NAD+ and of reduction of acetaldehyde and butyraldehyde by NADH catalysed by yeast alcohol dehydrogenase were studied. 2. Results for the aldehyde–NADH reactions are consistent with a compulsory-order mechanism with the rate-limiting step being the dissociation of the product enzyme–NAD+ complex. In contrast the results for the alcohol–NAD+ reactions indicate that some dissociation of coenzyme from the active enzyme–NAD+–alcohol ternary complexes must occur and that the mechanism is not strictly compulsory-order. The rate-limiting step in ethanol oxidation is the dissociation of the product enzyme–NADH complex but with the other alcohols it is probably the catalytic interconversion of ternary complexes. 3. The rate constants describing the combination of NAD+ and NADH with the enzyme and the dissociations of these coenzymes from binary complexes with the enzyme were measured.

scholarly journals Inhibition of microsomal oxidation of ethanol by pyrazole and 4-methylpyrazole in vitro Increased effectiveness after induction by pyrazole and 4-methylpyrazole

1986 ◽  
Vol 239 (3) ◽  
pp. 671-677 ◽  
Author(s):  
D E Feierman ◽  
A I Cederbaum
Keyword(s):  
Alcohol Dehydrogenase ◽  
Ethanol Oxidation ◽  
Liver Microsomes ◽  
Chronic Ethanol ◽  
Ethanol Metabolism ◽  
Ethanol Treatment ◽  
Previously Treated ◽  
Kinetics Of ◽  
Oxidation Of Ethanol

Pyrazole and 4-methylpyrazole, which are inhibitors of alcohol dehydrogenase, were also found to be effective inhibitors of the oxidation of ethanol by liver microsomes (microsomal fractions) in vitro. Ethanol oxidation by microsomes from rats previously treated for 2 or 3 days with either pyrazole or 4-methylpyrazole appeared to be especially sensitive to inhibition in vitro by pyrazole or 4-methylpyrazole. The kinetics of inhibition by pyrazole or 4-methylpyrazole in all microsomal preparations were mixed, as the Km for ethanol was elevated while Vmax was lowered. However, Ki values for pyrazole (about 0.35 mM) and especially 4-methylpyrazole (about 0.03-0.10 mM) were much lower than those found with the saline controls (about 0.7-1.1 mM). In contrast, Ki values for dimethyl sulphoxide as an inhibitor of microsomal ethanol oxidation were similar in all microsomal preparations. Pyrazole and 4-methylpyrazole reacted with microsomes to produce type II spectral changes whose magnitude increased after treatment with either pyrazole or 4-methylpyrazole. Thus the increased inhibitory effectiveness of pyrazole and 4-methylpyrazole appears to be associated with increased interactions with the cytochrome P-450 isoenzyme(s) induced by these compounds. These isoenzymes have properties similar to those of the isoenzyme induced by chronic ethanol treatment. Therefore, caution is needed in the use of pyrazole or 4-methylpyrazole to assess pathways of ethanol metabolism, especially after chronic ethanol treatment, since these agents, besides inhibiting alcohol dehydrogenase, are also effective inhibitors of microsomal ethanol oxidation.

scholarly journals Inhibition of catalase-dependent ethanol metabolism in alcohol dehydrogenase-deficient deermice by fructose

1987 ◽  
Vol 248 (2) ◽  
pp. 415-421 ◽  
Author(s):  
J A Handler ◽  
B U Bradford ◽  
E B Glassman ◽  
D T Forman ◽  
R G Thurman
Keyword(s):  
Alcohol Dehydrogenase ◽  
Ethanol Metabolism ◽  
Beta Oxidation ◽  
Low Concentrations ◽  
H2o2 Generation ◽  
Order Of Magnitude ◽  
Rate Limiting ◽  
Cytochrome P 450 ◽  
Generating System ◽  
Stimulation Of

Hepatic microsomal fractions from ADH (alcohol dehydrogenase)-negative deermice incubated with an NADPH-generating system metabolized butanol and ethanol at rates around 10 nmol/min per mg. In contrast, cytosolic catalase from ADH-negative deermouse liver oxidized ethanol, but not butanol, when incubated with an H2O2-generating system. Thus butanol is oxidized by cytochrome P-450 in microsomal fractions, but not by cytosolic catalase, in tissues from ADH-negative deermice. In perfused livers from ADH-negative deermice, rates of ethanol uptake at low concentrations of ethanol (1.5 mM) were about 60 mumol/h per g, yet butanol (1.5 mM) uptake was undetectable (less than 4 mumol/h per g). At higher concentrations of alcohol (25-30 mM), rates of ethanol uptake were about 80 mumol/h per g, whereas rates of butanol uptake were only about 9 mumol/h per g. Because rates of butanol metabolism via cytochrome P-450 in deermice were more than an order of magnitude lower than rates of ethanol uptake in livers from ADH-negative deermice, it is concluded that ethanol uptake by perfused livers from ADH-negative deermice is catalysed predominantly via catalase-H2O2. In support of this conclusion, rates of H2O2 generation, which are rate-limiting for the peroxidation of ethanol by catalase, were about 65 mumol/h per g in livers from ADH-negative deermice, values similar to rates of ethanol uptake of about 60 mumol/h per g measured under identical conditions. Rates of ethanol uptake by perfused livers from ADH-positive, but not from ADH-negative, deermice were increased by about 50% by infusion of fructose. Thus it is concluded that the stimulation of hepatic ethanol uptake by fructose is dependent on the presence of ADH. Unexpectedly, fructose decreased rates of ethanol metabolism and H2O2 generation by about 60% in perfused livers from ADH-negative deermice, probably by decreasing activation of fatty acids and thus diminishing rates of peroxisomal beta-oxidation.

Sign in / Sign up

Export Citation Format

Share Document