Kinetic properties of membrane-bound and Triton X-100-solubilized human brain monoamine oxidase

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Abstract

The kinetic properties of membrane-bound and Triton X-100-solubilized human brain mitochondrial type A and B monoamine oxidase were examined. These studies reveal that the Km values for phenylethylamine and benzylamine, type B monoamine oxidase substrates, were only slightly increased by the solubilization procedure. The Km value for 5-hydroxytryptamine, a type A monoamine oxidase substrate, was similarly increased by treatment with Triton X-100. The Km values for oxygen with all three amine substrates were unaffected by solubilization of the oxidase. Similarly, the optimum pH for deamination of substrates for the B isoenzyme was essentially unaltered in the solubilized preparation as compared to the membrane-bound enzyme whereas that for 5-hydroxytryptamine metabolism was decreased from pH 8.5 to approximately 7.75 on solubilization. The energy of activation with all three substrates was altered on solubilization of the oxidases with Triton X-100. The energy of activation for the B monoamine oxidase substrates increased whereas that for 5-hydroxytryptamine decreased. These data support the contention that the lipid environment surrounding the two forms of monoamine oxidase controls, in part, the activity and kinetic properties of the enzymes.

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This work was supported by grants from Public Health Service Grants #MH 29387 and HD 12044.

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