A sensitive photometric assay for monoamine oxidase.

A new spectrophotometric assay for the determination of monoamine oxidase activity is described. This simple and sensitive method is based on a coupled indicator reaction measuring the monoamine oxidase-dependent production of hydrogen peroxide. In this reaction the hydrogen peroxide-dependent oxidation of leuco-2′,7′-dichlorofluorescein to 2′,7′-dichlorofluorescein catalyzed by horseradish peroxidase is followed at 502 nm. Using benzylamine and seven biogenic amines as substrates, linear relationships between 2′,7′-dichlorofluorescein formation rate and monoamine oxidase concentration were found. The assay is especially suitable for determining substrate specificities for physiological amines as well as for inhibitor studies with pargyline or the monoamine oxidase A- and B-specific inhibitors clorgyline and deprenyl.