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

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 enzymically into the more cytotoxic species, 1,2(N)-dimethyl-6,7-dihydroxyiso-quinolinium ion, using enzyme sample prepared from human brain cortex. The values of the Michaelis constant and of the maximum velocity were 912 mu M and 1368 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.