Evidence has been presented that there are at least three forms of mitochondrial MAO in the mouse capable of deaminating kynuramine. These forms can be divided into two groups: one of these groups is inhibited by harmine but is relatively resistant to pargyline, while the other is resistant to harmine but is inhibited by low concentrations of pargyline. The harmine resistant group consists of two major forms with relatively short half-lives of 50°. The harmine sensitive fraction is apparently homogeneous with respect to thermal stability and has a significantly longer half-life than the harmine resistant forms. The relative proportions of these three forms vary greatly from one organ to another. It is suggested that some of the pharmacological effects of the MAO inhibitors may depend on specific inhibition of single forms.
