Platelet monoamine oxidase activity in schizophrenics -Kinetic aspects-

The present study was undertaken to study the relationship between changes in platelet monoamine oxidase (MAO) activity and schizophrenia. In addition, some biochemical characteristics of human platelet MAO were examined. The results are as follows; 1) There was no evidence to suggest that differences in methods used in the determination of platelet MAO activity caused the conflicting results in the literature. 2) It was confirmed from a kinetic study that MAO reaction in platelets proceeded via a ping-pong mechanism as previously reported in brain and liver. 3) The frequency distribution for the Michaelis constant (Km) and maximal velocity (Vmax) in apparently healthy subjects exhibited a skewed unimodal pattern. The mean of the Vmax value for females was significantly higher than the corresponding value for males. 4) Platelet MAO activity was determined in 8 schizophrenics and non-schizophrenic members from a North-Swedish pedigree with a high frequency of schizophrenia. There were no statistically significant differeneces in apparent Km and Vmax values between schizophrenics and their non-schizophrenic relatives, although a tendency to lowered Vmax and increased Km values was observed among the schizophrenic subjects. 5) MAO activity was assayed in platelets from 22 (8 monozygotic and 14 dizygotic) twin pairs. At least one twin (proband) of each pair suffered from serious psychiatric disorders including schizophrenia. The correlation between proband and control twins was high for both apparent Km and Vmax. No differences in kinetic properties were found between schizophrenic and non-schizophrenic twins. The monozygotic twin pairs showed very high correlations (Km; r=0.93, Vmax; r=0.86) as compared to dizygotic twins (Km; r=0.81, Vmax; r=0.50) and apparently healthy subjects (Km; r=0.46, Vmax; r=0.33).