Dataset Information

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

ABSTRACT: 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.

SUBMITTER: Handler JA

PROVIDER: S-EPMC1148557 | biostudies-other | 1987 Dec

REPOSITORIES: biostudies-other

ACCESS DATA

Similar Datasets

Project description:Lanthanides are utilized by microbial methanol dehydrogenases, and it has been proposed that lanthanides may be important for other type I alcohol dehydrogenases. A triple mutant strain (mxaF xoxF1 xoxF2; named MDH-3), deficient in the three known methanol dehydrogenases of the model methylotroph Methylobacterium extorquens AM1, is able to grow poorly with methanol if exogenous lanthanides are added to the growth medium. When the gene encoding a putative quinoprotein ethanol dehydrogenase, exaF, was mutated in the MDH-3 background, the quadruple mutant strain could no longer grow on methanol in minimal medium with added lanthanum (La3+). ExaF was purified from cells grown with both calcium (Ca2+) and La3+ and with Ca2+ only, and the protein species were studied biochemically. Purified ExaF is a 126-kDa homodimer that preferentially binds La3+ over Ca2+ in the active site. UV-visible spectroscopy indicates the presence of pyrroloquinoline quinone (PQQ) as a cofactor. ExaF purified from the Ca2+-plus-La3+ condition readily oxidizes ethanol and has secondary activities with formaldehyde, acetaldehyde, and methanol, whereas ExaF purified from the Ca2+-only condition has minimal activity with ethanol as the substrate and activity with methanol is not detectable. The exaF mutant is not affected for growth with ethanol; however, kinetic and in vivo data show that ExaF contributes to ethanol metabolism when La3+ is present, expanding the role of lanthanides to multicarbon metabolism.ImportanceExaF is the most efficient PQQ-dependent ethanol dehydrogenase reported to date and, to our knowledge, the first non-XoxF-type alcohol oxidation system reported to use lanthanides as a cofactor, expanding the importance of lanthanides in biochemistry and bacterial metabolism beyond methanol dehydrogenases to multicarbon metabolism. These results support an earlier proposal that an aspartate residue near the catalytic aspartate residue may be an indicator of rare-earth element utilization by type I alcohol dehydrogenases.

Dataset Information

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

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets