INTERACTION BETWEEN HUMAN-PLATELET MONO-AMINE OXIDASE, ITS MONO-AMINE SUBSTRATES AND OXYGEN

The interaction of human platelet MAO-B with three substrates (β-phenethylamine, tryptamine and benzylamine) has been investigated in an attempt to determine whether or not there exists heterogeneity of this enzyme form. Treatment with pargyline, thermal denaturation and 2-butanone affected the enzyme activity to the same degree, regardless of the amine substrate used. Mixed substrate experiments indicated that the substrates inhibited each other in a competitive manner with Ki values close to their Km values. The activity of MAO-B was increased in an uncompetitive manner as the oxygen concentration was raised. However, the degree of this increase was dependent upon the amine substrate used to assay for activity. These results are consistent for an enzyme with a single binding site for amine substrates and a possible multiplicity of binding sites for oxygen. © 1979.