Effect of perchlorate treatment on mitochondrial MAO-A and -B activities

Rat liver mitochondrial monoamine oxidase-A (MAO-A) and -B (MAO-B) were solubilized and isolated by procedures that included two cycles of treatment with a non-ionic detergent, Triton X-100, and then treatment with sodium perchlorate. After the treatment cycles with Triton X-100 about 23 and 36% of the original mitochondrial MAO-A and MAO-B activity, respectively, towards 0.1 mM serotonin and benzylamine remained in the residue. Of those activities, virtually no (2%) MAO-A activity, but appreciable (28%) MAO-B activity survived in the soluble state after the subsequent perchlorate treatment. The Km value and molecular turnover number of the soluble MAO-B, for benzylamine, were similar to those of the original activity in mitochondria, suggesting that this form of MAO has not undergone any qualitative change. After selective labelling of either form of MAO in mitochondria with 3H-pargyline and application of the isolation procedures, similar amounts of labelled MAO-A and -B were found in a soluble state, indicating that both forms of the enzyme were solubilized by the perchlorate treatment but that MAO-A was present in an inactivated state.