Comparison of the Properties of Semipurified Mitochondrial and Cytosolic Monoamine Oxidases from Rat Brain

Abstract: Mitochondrial and cytosolic monoamine oxidases were purified 220‐ and 129‐fold, respectively, from rat brain. The purification procedure involved extraction (without the use of detergents for mitochondrial monoamine oxidase), ammonium sulfate precipitation, and chromatography on Sephadex G‐25 and a DEAE‐cellulose column. The properties of both enzymes with kynuramine as substrate, including K_m values and pH optima at different kynuramine concentrations; the R_f values on polyacrylamide gel electrophoresis; and the thermal in‐activation patterns were different. 2‐Mercaptoethanol, together with heat treatment, released the flavin and decreased the enzyme activity differentially for the two enzymes. The absorption spectrum showed a “Red shift” in the absorption maxima when the spectra of the non‐Triton‐treated purified preparations were compared with those of the Triton‐treated ones, thus possibly revealing that the mitochondrial and the cytosolic monoamine oxidases may be two different enzyme entities.