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Wade H. Berrettini, MD; Walter Prozialeck, PhD; Wolfgang H. Vogel, PhD

Arch Gen Psychiatry. 1978;35(5):600-605.

Abstract
• Platelet monoamine oxidase (MAO) was kinetically evaluated in chronic schizophrenics and matched controls, using substrates of major physiologic importance and substrates of particular interest in the study of schizophrenia, such as serotonin (5-HT),N,N-dimethyltryptamine(DMT), 5-methoxytryptamine (5-MT), and dopamine (DA). Substrates were measured at six concentrations; values for maximal velocity (V_max) and Michaelis constant (K_m) were obtained by using Lineweaver-Burk plots.

The _Vmax was decreased for all substrates in chronic schizophrenia and the K_m was decreased for DA, 5-HT, and DMT, but remained unchanged for 5-MT. The value of K_m/V_max was similar for schizophrenics and normal persons when DA, 5-HT, and DMT were used as substrates, which may indicate that "uncompetitive" inhibition is responsible for the observed decrease in activity among chronic schizophrenics. The finding of a decreased V_max but unchanged K_m with 5-MT would be consistent with noncompetitive inhibition.

Author Affiliations
From the Departments of Psychiatry (Dr Berrettini) and Pharmacology (Drs Prozialeck and Vogel), and the Schizophrenia Research and Treatment Center (Drs Berrettini and Vogel), Jefferson Medical College, Philadelphia.

Footnotes
Accepted for publication Feb 22, 1978.

Reprint requests to Department of Pharmacology, Jefferson Medical College, 1020 Locust St, Philadelphia, PA 19107 (Dr Berrettini).

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