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Dimethylnitrosamine demethylation by reconstituted liver microsomal cytochrome P-450 enzyme system.

ABSTRACT: Oxidative demethylation of dimethylnitosamine was studied with both reconstituted and unresolved liver microsomal cytochrome P-450 enzyme systems from rats and hamsters. Proteinase treatment of liver microsomal preparations yielded cytochrome P-450 particulate fractions. Both cytochrome P-450 and NADPH- cytochrome c reductase fractions were required for optimum demethylation activity. Particulate cytochrome P-450 fractions were more effecient than either Triton X-100- or cholatesolubilized preparations of these particles in demethylation activity with rat and hamster liver preparations appear to be due to differences in specificity in their cytochrome P-450 fractions.

SUBMITTER: Lotlikar PD

PROVIDER: S-EPMC1172528 | biostudies-other | 1975 Dec

REPOSITORIES: biostudies-other

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Phospholipid requirement for dimethylnitrosamine demethylation by hamster hepatic microsomal cytochrome P-450 enzyme system.

Project description:Extraction with butan-1-ol of freeze-dried microsomal fractions from livers of 3-methyl-cholarthrene-pre-treated hamsters removed about 90% of the total lipid content, but the lipid remaining proved sufficient for the cytochrome P-450 enzyme system to retain about 15-40% of its original catalytic activity for dimethylnitrosamine demethylation. Addition of butan-1-ol-extracted total phospholipid or phosphatidylcholine could not restore any activity, whereas the addition of the synthetic phospholipid dilauroyl phosphatidylcholine was able to restore almost complete activity. Synthetic dipalmitoyl or distearoyl phosphatidylcholine was ineffective in restoring the activity in this reconstituted system.

| S-EPMC1164247 | biostudies-other

Ring-andN-hydroxylation of 2-acetamidofluorene by rat liver reconstituted cytochrome P-450 enzyme system.

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Phospholipid requirement for 2-acetamidofluorene N-and ring-hydroxylation by hamster liver microsomal cytochrome P-450 enzyme system.

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Studies on the mechanism of hepatic microsomal N-oxide formation. N-oxidation of NN-dimethylaniline by a reconstituted rabbit liver microsomal cytochrome P-448 enzyme system.

Project description:The N-oxidation of NN-dimethylaniline was studied by using a reconstituted rabbit liver microsomal enzyme system consisting of highly purified cytochrome P-448, NADPH-cytochrome c reductase and lipid factor. Both cytochrome P-448 and NADPH-cytochrome c reductase were required for optimum N-oxygenating activity; the catalytic capacity of the reductase fraction for supporting N-oxide formation varied with the isolation procedure applied. Addition of microsomal lipids to the assay media stimulated N-oxidation of the arylamine. N-Oxide formation appeared to be not generally controlled by electron transfer from cytochrome b5 to cytochrome P-448. The present work confirms that cytochrome P-448 can mediate about 44% of the rabbit liver microsomal N-oxidation of NN-dimethylaniline, thus reinforcing the existence of at least two distinct tertiary amine N-oxidases, i.e. haemoprotein and flavoprotein oxidase, in liver microsomal fractions.

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| S-EPMC1161830 | biostudies-other

Histidine residues in rabbit liver microsomal cytochrome P-450 2B4 control electron transfer from NADPH-cytochrome P-450 reductase and cytochrome b5.

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| S-EPMC1217696 | biostudies-other

Characterization of a phenobarbital-inducible cytochrome P-450, NADPH-cytochrome P-450 reductase and reconstituted cytochrome P-450 mono-oxygenase system from rat brain. Evidence for constitutive presence in rat and human brain.

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Alterations in microsomal electron transport, oxidative N-demethylation and azo-dye cleavage in carbon tetrachloride and dimethylnitrosamine-induced liver injury.

Project description:The effect of administration of carbon tetrachloride and dimethylnitrosamine in vivo on hepatic microsomal function related to drug metabolism was measured. It was found that the capacity of isolated microsomes to demethylate dimethylaniline was diminished during the first hour after carbon tetrachloride poisoning and during the second hour after dimethylnitrosamine poisoning. Thereafter the microsomes from carbon tetrachloride-poisoned livers showed a continuous decline in activity so that at 24hr. there was little residual capacity to undertake demethylation. Microsomes from dimethylnitrosamine-poisoned animals were not different from controls at 24hr. During the first 3hr. there was a transient rise in the accumulation of the N-oxide intermediate in carbon tetrachloride-poisoned livers, with a subsequent fall to below control values. In dimethylnitrosamine poisoning there was a parallel decrease in N-oxide accumulation with decreased demethylation. In the latter part of the first 24hr. the ratio of N-oxide accumulation to demethylation was increased in both instances. At 2hr. after poisoning with either compound there was no evidence of altered NADPH(2)-dependent neotetrazolium reduction or lipid peroxidation. NADPH(2)-dependent azo-dye cleavage was decreased. There was no difference in microsomal cytochrome b(5) content, but there was a decrease in the amount of cytochrome P-450. This latter change was correlated with the decreased capacity for NADPH(2)-dependent oxidative demethylation. It is suggested that dimethylnitrosamine is associated with a defect in microsomal NADPH(2)-dependent electron transport at the level of cytochrome P-450. In addition to affecting cytochrome P-450, carbon tetrachloride is associated with a second severe block involving the release of formaldehyde from the N-oxide intermediate.

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An enzyme-linked immunoadsorbent assay for measuring cytochrome b5 and NADPH-cytochrome P-450 reductase in rat liver microsomal fractions. Evidence for functionally inactive protein.

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| S-EPMC1153262 | biostudies-other

Alcohol Metabolizing Enzymes, Microsomal Ethanol Oxidizing System, Cytochrome P450 2E1, Catalase, and Aldehyde Dehydrogenase in Alcohol-Associated Liver Disease.

Project description:Once ingested, most of the alcohol is metabolized in the liver by alcohol dehydrogenase to acetaldehyde. Two additional pathways of acetaldehyde generation are by microsomal ethanol oxidizing system (cytochrome P450 2E1) and catalase. Acetaldehyde can form adducts which can interfere with cellular function, leading to alcohol-induced liver injury. The variants of alcohol metabolizing genes encode enzymes with varied kinetic properties and result in the different rate of alcohol elimination and acetaldehyde generation. Allelic variants of these genes with higher enzymatic activity are believed to be able to modify susceptibility to alcohol-induced liver injury; however, the human studies on the association of these variants and alcohol-associated liver disease are inconclusive. In addition to acetaldehyde, the shift in the redox state during alcohol elimination may also link to other pathways resulting in activation of downstream signaling leading to liver injury.

| S-EPMC7148483 | biostudies-literature

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