Purification of endogenous modulators of monoamine oxidase from plasma

A partial purification of endogenous modulators of monoamine oxidase-A (MAO-A) and MAO-B from human plasma has been achieved through Sephadex, ion-exchange and affinity chromatography. The MAO-A modulator had a molecular weight of about 4,000, was acidic or neutral, and did not contain the carbohydrate moiety mannose. It was thermostable but sensitive to trypsin treatment. It inhibited MAO-A activity in a sonically disrupted mitochondrial preparation prepared from bovine striatum in a dose-dependent manner and altered the kinetic parameters of MAO-A by increasing the K m and decreasing the V max. The concentration of the MAO-A modulator was higher than that of the MAO-B modulators, which had molecular weights of about 7,000, 14,000 and > 30,000 respectively. The MAO-B modulators increased the K m for tryptamine without changing the V max. These data indicate that human plasma contains peptides that may function as endogenous regulations of platelet MAO. The significance of this finding in relation to psychiatric disorders is discussed.