[Determination of monoamine oxidase and catechol-O-methyltransferase in human blood components: methodical aspects (author's transl)].

Controversal findings are reported with respect to alternations in activity of monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) in psychoses. Initially we determined the interindividual differences of some biochemical properties of the two enzymes in normal control subjects. Platelet rich plasma and lysate of red blood cells, respectively, were used for assay. Enzyme activity was referred to mg of protein or mg hemoglobin and number of platelets, respectively. Substrates used for COMT assay were: 3,4-dihydroxybenzaldehyde and 3,4-dihydroxybenzoic acid; for MAO determination: tyramine, tryptamine and phenylethylamine. Interindividual as well as intraindividual differences in the biochemical characteristics (apparent Km, Vmax, IC50, meta/para ratio of O-methylation in vitro) were remarkably low, the coefficient of variation was in the range of 30%.