Inhibition of Type A and Type B Monoamine Oxidase by Isogentisin and its 3-O-Glucoside

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Abstract
Isogentisin and its 3-O-glucoside were found to inhibit monoamine oxidase (MAO) in rat brain mitochondria in vitro using 5-hydroxytryptamine (5-HT) and (3-phenylethylamine (PEA) as relatively specific substrates for type A and type B MAO, respectively. Isogentisin showed much more potent MAO inhibition than its 3-O-glucoside for both substrates. The inhibition by both compounds was fully competitive for both substrates. Both compounds were found to be almost nonselective inhibitors for type A and type B MAO. popular medicine both in Europe and Asia due to their unique actions on the central nervous system [2]. In our previous preliminary communication [3], we briefly reported that isogentisin and its 3-O-glucoside inhibit monoamine oxidase (MAO) in vitro using kynuramine as substrate. Since mitochondrial MAO is believed to exist in many animal tissues in two functional forms called type A and type B [4-6], in the present paper we have studied MAO inhibition by isogentisin and its 3-O-glucoside using 5-hydroxytryptamine (5-HT) and (3-phenylethylamine (PEA) as relatively specific substrates for type A and type B MAO, respectively.