Deamination of 5‐Hydroxytryptamine by Both Forms of Monoamine Oxidase in the Rat Brain

Abstract
K m and Vmax values of monoamine oxidase (MAO) A and B towards 5-hydroxytryptamine were determined for rat brain homogenates after the in vitro inhibition of one of the two forms by the selective inhibitors clorgyline and l-deprenyl. Km values of 178 and 1170μm, and Vmax values of 0.73 and 0.09 nmol·mg protein−1·min−1 towards 5-hydroxytryptamine were found for MAO-A and -B, respectively. The K1 for 5-hydroxytryptamine as a competitive inhibitor of β-phenethylamine oxidation by MAO-B was found to be 1400 μm. The significance of these findings is discussed.