NADH-dependent polyvanadate reduction by microsomes

NADH-dependent redn. of polyvanadate was obsd. by using rat liver microsomes as the enzyme source. The reduced vanadate obtained was blue in color, with a broad absorption max. in the red region at .apprx.650 nm. Microsomes and phosphate anions were essential for polyvanadate redn. The rate and the extent of formation of the blue-colored compd. depended on the amt. of vanadate present. Cytochrome b5 was involved in this superoxide dismutase-insensitive reaction. The rate of disappearance of the blue-colored compd. was dependent on the concn. of NADH and was sensitive to SOD. Catalase and $Mn^{2+}$, which inhibit the O consumption accompanying NADH oxidn., increased both the rate and extent of the blue-colored compd. formed. Vanadate apparently acts an electron acceptor