Abstract

The extraction of lipids from rat liver mitochondrial membranes by 2-butanone treatment inhibited the activity of membrane-bound monoamine oxidase -A but not -B. For the -B form, the apparent Michaelis constants of the enzyme towards oxygen and the maximum molecular turnover numbers obtained when beta-phenethylamine and benzylamine were used as substrates were not significantly changed by the lipid-depletion procedure, but the values of the Michaelis constant towards benzylamine was significantly increased after lipid-depletion. The differential sensitivity of beta-phenethylamine and benzylamine oxidation to inhibition by Tris-HCl was not changed after lipid-depletion. The results are consistent with the hypothesis that the mitochondrial membrane lipids, while essential for the activity of the -A form of the enzyme in rat liver, play a more subtle modulatory role in the activity of the -B form.

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