Abstract
Prostaglandin D 2 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 prostaglandins D 1, D 2, D 3 and H 2 and various carbonyl compounds (e.g., phenanthrenequinone and nitrobenzaldehyde, etc.). Prostaglandin D 2 was reduced to 9α,11β-prostaglandin F 2 and prostaglandin H 2 to prostaglandin F 2α with NADPH as a cofactor. Phenanthrenequinone competitively inhibited the reduction of prostaglandin D 2, while it did not inhibit that of prostaglandin H 2. Moreover, chloride ion stimulated the reduction of prostaglandin D 2 and carbonyl compounds, while it had no effect on that of prostaglandin H 2. 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 D 2 and carbonyl compounds and the other for prostaglandin H 2, 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 K m value for prostaglandin D 2 (10 μ m for the liver enzyme and 120 μ m for the lung enzyme), the sensitivity to chloride ion (threefold greater activation for the liver enzyme) and the inhibition by CuSO 4 and HgCl 2 (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.
Published Version
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