Monkey platelet monoamine oxidase (MAO) was preferentially found as the B-form of the enzyme as observed from differences in substrate specificities, as well as liver MAO. The isoelectric points and molecular weights of platelet MAO subunits were compared with those of monkey liver using sodium dodecyl sulfate-disc polyacrylamide gel electrophoresis and isoelectric focusing-disc gel electrophoresis. The pI value of monkey liver was a single peak at 6.5, but the pI values of monkey platelets were triple peaks at 5.5, 6.5 and 7.0. The molecular weight of MAO subunits in monkey platelets was similar to that of liver, and was found to be about 60,000. These results indicate that MAO-B of monkey platelets differs from MAO-B of the liver, and that it has different electrophoretic properties.
