Monoamine oxidase activity and enzyme kinetics in three subpopulations of density-fractionated platelets in chronic paranoid schizophrenics.

Platelet monoamine oxidase (MAO) activity was studied in three subpopulations of density-fractionated platelets in 15 unmedicated chronic paranoid schizophrenic patients and contrasted with normal controls. No significant difference in MAO activity was found in any of the three platelet fractions in schizophrenics compared to controls. Enzyme kinetic studies performed on the intermediate-density platelet fraction demonstrated no significant differences in Vmax or Michaelis' constant (Km) between schizophrenics and controls, but showed that the higher platelet MAO activity reported in females compared to male is due to a significantly greater Vmax rather than altered Km. It is suggested that conflicting results reported in the literature regarding platelet MAO in schizophrenia are not related to the platelet subpopulations studied but are largely due to the selected patient populations.