Colorimetric assay for monoamine oxidase in tissues using peroxidase and 2,2'-azinodi(3-ethylbenzthiazoline-6-sulfonic acid) as chromogen.

Monoamine oxidase is assayed in tissue by a colorimetric reaction using horse radish peroxidase and 2,2'-azinodi(ethylbenzthiazoline-6-sulfonic acid to measure H2O2 formed during oxidation of amines. The method has a coefficient of variation of approximately 2.5% and provides results comparable with those of radiometric assay. Monoamine oxidase activities in rat liver mitochondria and crude mitochondrial fraction from brain and with tyramine as a substrate were 18.9 +/- 0.4 and 4.61 +/- 0.15 nmol/min/mg of protein, respectively, using this method. Kinetic parameters of liver and brain monoamine oxidase with various substrates and inhibitors appeared to be the same when determined by either colorimetric or radiometric methods.