Enzymatic oxidation of the dopaminergic neurotoxin, 1(R), 2(N)-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, into 1,2(N)-dimethyl-6,7-dihydroxyisoquinolinium ion

Abstract

The dopamine-derived alkaloid, 1(R),2(N)-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline [N-methyl(R)salsolinol] was found to be oxidized enzymatically into the more cytotoxic species, 1,2(N)-dimethyl-6,7-dihydroxyisoquinolinium ion, using enzyme sample prepared from human brain cortex. The values of the Michaelis constant and of the maximum velocity were 912 microM and 1,368 pmol/min/mg protein, respectively. The enzyme was not inhibited by inhibitors of monoamine oxidase, but was sensitive to semicarbazide. The oxidation is discussed in relation to the dopaminergic neurotoxicity of N-methyl-(R)salsolinol.