REDUCTION OF DIHYDROXYPHENYLACETIC ACID BY A NOVEL ENZYME IN THE RAT-BRAIN

A novel enzyme that converts dihydroxyphenylacetic acid (DOPAC) to dihydroxyphenylethanol (DOPET) was found to be present in the microdialysate of the rat brain. :The enzyme, named DOPAC reductase, was inhibited by EDTA and stimulated by divalent cations like Zn2+ Mn2+, Co2+ and Cu2+. Its K-m, pH optimum and temperature optimum were found to be 32 +/- 2 mu M, 7.5 and 40 degrees, respectively. The equivalent acid metabolite of noradrenaline, 3, 4-dihydroxymandelic acid, and the methoxylated acids of both noradrenaline and dopamine, 3-methoxy-4-hydroxymandelic acid and 3-methoxy-4-hydroxyphenylacetic acid, were found not to be substrates of DOPAC reductase. Thus, DOPAC reductase may be an enzyme that is specifically involved in the one-step conversion of DOPAC to DOPET in the central metabolism of dopamine.