A CONVENIENT SPECTROPHOTOMETRIC ASSAY FOR MONOAMINE OXIDASE

A rapid, convenient, and sensitive assay of monoamine oxidase activity in whole homogenates and partially purified preparations of monoamine oxidase has been developed. The assay depends upon the production of p-dimethylaminobenzaldehyde (ε{lunate} = 2.77 × 104 at 355 mμ) from p-dimethylaminobenzylamine. Although the substrate is oxidized at a lower rate than benzylamine, the high extinction coefficient of the product at 355mμ makes the assay useful. The product of the reaction, p-dimethylaminobenzaldehyde, is not further metabolized, probably because it is a poor substrate for aldehyde and alcohol dehydrogenases. Thus, the assay can be carried out even in whole liver homogenates that are known to contain large amounts of enzymes that might be expected to interfere. © 1969.