Inhibitory effects of Triton X-100 and some other detergents on a new type, distinct from type A and B, of monoamine oxidase in carp liver mitochondria.

Abstract

We examined the inhibitory effects of Triton X-100 and some other detergents on a new type of MAO, distinct from both MAO-A and MAO-B, in carp liver mitochondria. SDS, octyl-β-D-glucopyranoside, sodium cholate and Triton X-100, at relatively low concentrations, caused strong inhibition of activity towards tyramine, but digitonin caused only weak inhibition. SDS, octyl-β-D-glucopyranoside and cholate caused almost complete inhibition of activity at the concentrations tested. The extent of inhibition by Triton X-100 was greater after preincubation at 37°C for 30 min than that without preincubation; but with or without preincubation, the inhibition was not substrate-selective and was not complete at 2% of detergent. Without preincubation, the mode of inhibition by Triton X-100 was competitive and reversible with respect to the oxidations of 5-HT, tyramine and β-phenylethylamine; but after preincubation, it became non-competitive and irreversible, depending on the concentration of detergent used. These findings support our previous conclusion on the homogeneity of carp liver MAO and suggest that Triton X-100 acts differently upon the enzyme, depending on both preincubation and the concentration of detergent used.