A simple and sensitive spectrophotometric determination of monoamine oxidase activity.

A simple, sensitive Spectrophotometric determination of monoamine oxidase activity from tissue homogenates is described. This method is based on the high extinction coefficient of 4-hydroxy-3-methoxy-benzaldehyde (vanillin) at 345 nm at pH ~ 11.7. Vanillin is formed by inonoamine oxidase when 4-hydroxy-3-methoxy-benzylamine is used as substrate. The primary oxidation product, 4-hydroxy-3-methoxybenzaldehyde, is not further metabolized by aldehyde reductase or aldehyde dehydrogenase. The apparent Km value of 4-hydroxy-3-methoxy-benzylamine for monoamine oxidase of rat brain is 150 to 180 /^mol/1 (pH 7.0). The pH optimum of the rat brain monoamine oxidase with this substrate was found to be at about 9.0. Inhibition of monoamine oxidase of rat brain after pretreatment of rats with iproniazid, pargyline and tranylcypromine was investigated with this method. The data were analyzed according to LINEWEAVER and BUR .