NADH-dependent polyvanadate reduction by microsomes.

NADH-dependent reduction of polyvanadate was observed by using rat liver microsomes as the enzyme source. The reduced vanadate form obtained was blue in color with a broad absorption maximum in the red region around 650 nm. Microsomes and phosphate anions were found to be essential for polyvanadate reduction. The rate and the extent of formation of blue color compound was dependent on the amount of vanadate present. Cytochrome b5 was found to be involved in this SOD-insensitive reaction. The rate of disappearance of the blue-colored compound was dependent on concentration of NADH and was found to be sensitive to SOD. Catalase and Mn2+, which inhibit oxygen consumption accompanying NADH oxidation, increased both the rate and extent of the blue color compound formed. The results suggest that vanadate acts as an electron acceptor.