Purification and characterization of prostaglandin F synthase from bovine liver

Prostaglandin D2 11-ketoreductase activity of bovine liver was purified 340-fold to apparent homogeneity. The purified enzyme was a monomeric protein with a molecular weight of about 36 kDa, and had a broad substrate specificity for porstaglandins D1, D2, D3, and H2, and various carbonyl compounds (e.g., phenanthrenequinone and nitrobenzaldehyde, etc.). Prostaglandin D2 was reduced to 9 alpha,11 beta-prostaglandin F2 and prostaglandin H2 to prostaglandin F2 alpha with NADPH as a cofactor. Phenanthrenequinone competitively inhibited the reduction of prostaglandin D2, while it did not inhibit that of prostaglandin H2. Moreover, chloride ion stimulated the reduction of prostaglandin D2 and carbonyl compounds, while it had no effect on that of prostaglandin H2. Besides, the enzyme was inhibited by flavonoids (e.g., quercetin) that inhibit carbonyl reductase, but was not inhibited by barbital and sorbinil, which are the inhibitors of aldehyde and aldose reductases, respectively. These results indicate that the bovine liver enzyme has two different active sites, i.e., one for prostaglandin D2 and carbonyl compounds and the other for prostaglandin H2, and appears to be a kind of carbonyl reductase like bovine lung prostaglandin F synthase (Watanabe, K., Yoshida, R., Shimizu, T., and Hayaishi, O., 1985, J. Biol. Chem. 260, 7035-7041). However, the bovine liver enzyme was different from prostaglandin F synthase of bovine lung with regard to the Km value for prostaglandin D2 (10 microM for the liver enzyme and 120 microM for the lung enzyme), the sensitivity to chloride ion (threefold greater activation for the liver enzyme) and the inhibition by CuSO4 and HgCl2 (two orders of magnitude more resistant in the case of the liver enzyme). These results suggest that the bovine liver enzyme is a subtype of bovine lung prostaglandin F synthase.