Abstract

The interaction between clorgyline and the Type-A monoamine oxidase (MAO-A) in homogenates and mitochondrial fractions of the rat heart appears to take place almost entirely at specific binding sites. After an initial reversible interaction, the inhibition of enzyme activity becomes irreversible in the presence of concentrations of clorgyline of the same order as that of the enzyme. Use has been made of this relationship (1) to determine the molecular turnover numbers of the enzyme toward three substrates for the A-form: serotonin, tyramine and β-phenethylamine and (2) to determine the concentration of enzyme active centers in homogenates and mitochondrial fractions of rat hearts. As the rats grew older, both the specific activity of MAO-A, and the concentration of clorgyline/(mg protein) required to cause inhibition of the enzyme activity increased in a parallel fashion. It was concluded that the concentration of active centers of the MAO-A also increased with age. The usefulness of this method of determining the concentration of MAO-A is discussed.