Radiochemical Assay of Monoamine Oxidase Activity

The activity of monoamine oxidase enzymes may be quantified by measuring the conversion of a radiolabeled amine substrate to a radiolabeled product that occurs during incubation of the substrate with the enzyme in an aqueous buffer. Described herein is an established discontinuous procedure in which separation of the substrate and product is achieved by extracting uncharged aldehydes into an organic solvent, while cationic amines remain in an acidified aqueous layer. Under assay conditions designed to ensure a pseudo-linear catalytic rate for the duration of the incubation, determination of radioactivity in the organic solvent by liquid scintillation counting facilitates estimation of an initial rate for amine turnover.