Electron microscopic localization of monoamine oxidase in the rat liver

Summary Two methods have been employed to localize monoamine oxidase activity in the cells of rat liver, using either 2-(2′-benzothiazolyl)-5-stryl-3-(4′-phtalhydrazidyl) tetrazolium chloride (BSPT) or ferricyanide as electron acceptor. With both methods monoamine oxidase activity was found both in the inner and the outer mitochondral membrane, although the outer membrane appeared the most probable location. In addition the BSPT method but not the ferricyanide method, revealed monoamine oxidase activity in the endoplasmatic reticulum. The results obtained by the two methods have been compared and are discussed in view of available biochemical data on monoamine oxidase. Supported by research grants from the National Research Council of Canada (A 3651), The Swedish Medical Research Council (4145) and M. Bergwall's Foundation, Stockholm.