Inhibition of type A monoamine oxidase by coptisine in mouse brain

The inhibitory effects of coptisine, a protoberberine isoquinoline alkaloid, on type A and type B monoamine oxidase (MAO-A and MAO-B) activities in mouse brain were investigated. Coptisine showed an inhibitory effect on MAO-A activity in a concentration-dependent manner using a substrate kynuramine, but coptisine did not inhibit MAO-B activity. Coptisine exhibited 54.3% inhibition of MAO-A activity at 2 microM. The values of Km and Vmax of MAO-A were 151.9 +/- 0.6 microM and 0.40 +/- 0.03 nmol/min/mg protein, respectively (n=5). Coptisine competitively inhibited MAO-A activity with kynuramine. The Ki value of coptisine was 3.3 microM. The inhibition of MAO-A by coptisine was found to be reversible by dialysis of the incubation mixture. These results suggest that coptisine is a potent reversible inhibitor of MAO-A, and that coptisine functions to regulate the catecholamine content.