[Effect of solubilization by methylethylketone of rat liver mitochondrial monoamine oxidase on inhibition by clorgyline and deprenyl of the enzyme activity].

A comparative study of the inhibitory effect of clorgyline and deprenyl on serotonin, beta-phenylethylamine and tyramine deamination by intact mitochondria as well as by solubilized with methylethylketone and partially purified monoamine oxidase (MAO) from rat liver was carried out. The effect of 4-ethylpyridine on this process was investigated. After solubilization of MAO by methylethylketone 7% of mitochondrial activity passes into solution and the rate of deamination of serotonin, tyramine and beta-phenylethylamine by soluble MAO preparation is selectively decreased. The corresponding residual activities are equal to 29, 63, 86 and 92%. The inhibitory effect of clorgyline on serotonin deamination by soluble MAO preparations is considerably lower than that by mitochondrial suspensions at the concentrations of the inhibitor from 1 x 10(-4) to 1 x 10(-7) M, while the inhibitory action of clorgyline on tyramine deamination after MAO solubilization by methylethylketone is increased at 10(-4) and 10(-5) M, but decreased insignificantly at 10(-6) and 10(-7) M. When solubilized MAO preparations are used, 4-ethylpyridine introduced into the sample before or after preincubation of the enzyme with clorgyline (30 min, 23 degrees) eliminates the inhibitory action of the latter on serotonin and tyramine deamination, thus suggesting the reversibility of the inhibitory effect of clorgyline. In similar experiments with mitochondrial suspensions the inhibition by clorgyline of deamination of these amines is irreversible. Similar experiments on mitochondrial suspensions showed that clorgyline irreversibly inhibits the deamination of these amines. The rate of inhibition by deprenyl of beta-phenylethylamine oxidation due to MAO solubilization by methylethylketone is not changed. 4-Ethylpyridine added to the samples before or after preincubation of deprenyl with the enzyme (30 min, 23 degrees) abolishes the inhibiting effect of the former both in soluble MOA and in mitochondrial suspensions. This suggests that under the given experimental conditions the inhibiting effect of deprenyl is reversible. Possible nature of MAO forms A and B is discussed.