Activation of monoamine oxidase by high molecular weight fractions of human plasma.

The activation of human platelet monoamine oxidase (MAO) and rat brain mitochondrial MAO ( RBM -MAO) by human plasma were studied. The deamination of two different substrates, tyramine and phenethylamine (PEA) was investigated. The increase in MAO activity in the presence of human plasma can be explained by the observed decrease in the apparent Km for the amine (tyramine, PEA). This activation pattern was the same both for human platelet MAO and RBM -MAO. The activating properties of human plasma were recovered in high molecular weight fractions after gel filtration.