Comparison of biochemical properties of platelet monoamine oxidase in mentally disordered and healthy individuals.

We have investigated some biochemical properties of platelet monoamine oxidase (MAO) isolated from chronic schizophrenic and agoraphobic patients, nonschizophrenic institutional controls, and healthy volunteers. The enzyme activity level in the healthy population was reasonably constant over at least a 6-week period. High correlations were found between MAO activity assessed for different substrates (p-tyramine, beta-phenylethylamine, and tryptamine). Some heterogeneity of the platelet MAO may exist, however, at least in some of the chronic schizophrenics, since the substrate specificities were changed and the Km values reduced. The half-life of the enzyme at 58 degrees C was 2-3 minutes and the transition temperature derived from Arrhenius plots was 16-17 degrees C with respect to beta-phenylethylamine. Platelet MAO from chronic schizophrenics was not significantly different from control values with respect to temperature effects. SDS-polyacrylamide gel electrophoresis of the 3H-pargyline-MAO adduct revealed that the subunit of platelet MAO is a single band protein with a molar individuals. The adjacent structure of the flavine site of the platelet MAO was chromatographically identical to the penta-peptide isolated from MAOs from other tissues. The response of platelet MAO to thimerosal, a new differential type A MAO inhibitor, could be distinguished not only from type A MAO isolated from human placenta, but also from type B MAO isolated from bovine liver.