THE INTERACTIONS OF MILACEMIDE WITH MONOAMINE-OXIDASE

The interactions of the anticonvulsant drug milacemide (2-n-pentylamin oacetamide) with rat liver mitochondrial monoamine oxidases-A and -B h ave been studied. The compound acts as a substrate for the B-form of t he enzyme, with an apparent K-m value of 49 +/- 4.7 mu M and a V-max v alue of 1.1 +/- 0.2 nmol/min/mg. It is also a time-dependent irreversi ble inhibitor of that enzyme. Any activity of monoamine oxidase-A towa rds this substrate was too low to allow accurate determinations to be made by either luminometric determination of H2O2 formation or spectro photometric coupling of aldehyde formation to NAD(+) reduction in the presence of aldehyde dehydrogenase. Milacemide was a reversible compet itive inhibitor towards monoamine oxidase-A. The inhibitor constant (K -i) was 115 a 35 mu M indicating a higher affinity than that towards m onoamine oxidase-B, which was also competitively inhibited in the abse nce of enzyme-inhibitor preincubation (K-i = 331 +/- 185 mu M). Determ ination of the formation of H2O2 and the aldehyde product of the oxida tive cleavage of milacemide by purified monoamine oxidase-B from ox li ver indicated that cleavage resulted solely in the formation of pentan al and glycinamide. There was no evidence for alternative cleavage to pentylamine and oxamaldehyde.