Inhibitory effect of NAD(P)H:quinone oxidoreductase on autoxidation of 6-hydroxydopa and 6-hydroxydopamine

6-Hydroxydopa and 6-hydroxydopamine undergo autoxidation in the presence of molecular oxygen giving rise to the corresponding p-quinones. NAD(P)H:quinone oxidoreductase (QR) purified from Glycine max showed that it inhibited autoxidation of 6-hydroxydopa and 6-hydroxydopamine. The inhibition of autoxidation of 6-hydroxydopa was greater than B-hydroxydopamine. QR had a potentiated effect in preventing 6-hydroxydopa oxidation in the presence of catalase and superoxide dismutase. Reduced glutathione increased protective effect when incubated with QR on both 6-hydroxydopa and B-hydroxydopamine. Homogenized tissues from rat brain also showed to inhibit 6-hydroxydopa autoxidation. Our observations suggest a possible role for brain NAD(P)H:quinone oxidoreductase in protection of neurons from the toxic effect of quinones.