Kinetic analysis of platelet monoamine oxidase in chronic schizophrenia

Km and Vmax values for platelet monoamine oxidase (MAO) were determined in 16 chronic schizophrenics and 18 controls utilizing three substrates, tyramine (TYR), benzylamine (BZ), and phenylethylamine (PEA). In the chronic schizophrenics decreased Km and Vmax values were found for TYR and BZ but not PEA. When prior neuroleptic drug exposure was considered, a trend toward lower kinetic parameters was found in schizophrenics with a history of prior neuroleptic usage. We conclude that platelet MAO activity is, in chronic schizophrenics, both quantitatively reduced and qualitatively different from control enzyme. We suggest that the measurement of Km in addition to the measurement of Vmax may be a useful biological marker for chronic schizophrenia providing that the appropriate substrates are employed.