Vanadate Enhancement of the Oxidation of NADH by O2(-): Effects of Phosphate and Chelating Agents

摘要

Vanadate markedly stimulated the oxidation of NADH by plasma membranes from liver or erythrocytes and this effect was eliminated by superoxide dismutase (SOD)3. It appeared possible that he plasma membranes were generating O2(-) in the presence of NAD(P)H and that vanadate might catalyze the oxidation of NAD(P)H yb O2(-), and by showing that either vanadate or molybdate would enhance the oxidation of NAD(P)H and that SOD, but not catalase, eliminated this effect. Vanadate markedly stimulated the oxidation of NADH by O2(-). Both phosphate and Tris are inhibitory, but phosphate diminishes the greater inhibitory effect of Tris and thus gives the appearance of stimulating when added to Tris-buffered reaction mixtures. Chelating agents moderately increased the oxidation of NADH but eliminated the much grater catalytic effect of vanadate. Desferal was the most effective of the chelating agents, and could be used to titrate vanadate spectrophtometrically or in terms of the diminution of its catalytic activity. This permitted the demonstration that metavanadate or orthovanadate was the catalytically active species.