Alpha-methyl derivatives of biogenic amines as inhibitors of monoamin oxidase

The values of Km app and Vmax for three natural substrates of monoamine oxidase have been determined at various stages in the isolation of the enzyme from rat liver tissue. The results are consistent with the presence in the enzyme preparation of at least two distinct molecular forms of the enzyme. Using the alpha-methyl derivatives of the natural substrates as inhibitors of the enzyme, the substrate dependence of Ki further substantiates this view. In addition, the kinetics of the inhibition suggest that the value of Km app may not for all substrates, necessarily be a measure of the affinity of the substrate for the enzyme.