Estrogen synthetase in the horse. Comparison of equine placental and rat liver NADPH-cytrochrome c (P-450) reductase activities.

NADPH-cytochrome c (P-450) reductases from horse placenta and rat liver were purified and their biological activities compared using cytochrome c as substrate. Rat liver reductase was purified to electrophoretic homogeneity in one chromatographic step on 2',5'-ADP agarose, and had a relative mass of 85,000 Da as estimated by SDS-PAGE. Equine placental reductase was separated from cytochrome P-450 on aminohexyl-Sepharose 4B and further purified on 2',5-ADP agarose; this preparation exhibited two bands, one of 85,000 and one of 80,000 Da, on SDS-PAGE. The lower molecular weight form was assumed to be a proteolytic product of the higher molecular weight form. A high retention of activity was obtained in both preparations. Equine placenta and rat liver enzymes were found to exhibit very similar Vmax and Km, suggesting that they are not species specific.