Clorgyline and deprenyl insensitive monoamine oxidase in rat brain soluble fraction.

A substantial percentage of monoamine oxidase activity was found in the soluble fraction of rat brain homogenates. The enzyme was not inhibited in vivo by high doses of clorgyline and deprenyl (12 mg/kg for 2 hr). Monoamine oxidase activity associated with the soluble fraction did not show the usual biphasic dose-response kinetics with clorgyline when kynuramine was used as the substrate. The present data show that there may be a new form of monoamine oxidase associated with the soluble fraction of the cell which has properties different from the two well-known monoamine oxidases A and B.