Human Plasma Monoamine Oxidase

Although this human plasma enzyme was shown (1) to have certain characteristics in common with plasma amine oxidases from other mammals (2-6), it could be distinguished from these other plasma enzymes by its substrate specificity. During studies relating to the substrate specificity of the human enzyme, the oxidation of aliphatic amines was noted to have a number of distinctive kinetic features. These consist chiefly of inhibition at high substrate concentration, strict dependence of apparent Michaelis and inhibitor constants upon pH, and contributions of nonpolar residues of substrates to their affinities for the enzyme. None of these features appears to have been recognized in previous studies with other plasma amine oxidases. These findings indicate certain characteristics of the active center of the human plasma enzyme.