Enzymatic formation of prostaglandin F2 alpha in human brain

Prostaglandin (PG)E2 9-ketoreductase, which catalyzes the conversion of PGE2 to PGF2 alpha, was purified from human brain to apparent homogeneity. The molecular weight, isoelectric point, optimum pH, Km value for PGE2, and turnover number were 34,000, 8.2, 6.5-7.5, 1.0 mM, and 7.6 min-1, respectively. Among PGs tested, the enzyme also catalyzed the reduction of other PGs such as PGA2, PGE1, and 13,14-dihydro-15-keto PGF2 alpha, but not that of PGD2, 11 beta-PGE2, PGH2, PGJ2, or delta 12-PGJ2. The reaction product formed from PGE2 was identified as PGF2 alpha by TLC combined with HPLC. This enzyme, as is the case for carbonyl reductase, was NADPH-dependent, preferred carbonyl compounds such as 9,10-phenanthrenequinone and menadione as substrates, and was sensitive to indomethacin, ethacrynic acid, and Cibacron blue 3G-A. The reduction of PGE2 was competitively inhibited by 9,10-phenanthrenequinone, which is a good substrate of this enzyme, indicating that the enzyme catalyzed the reduction of both substrates at the same active site. These results suggest that PGE2 9-ketoreductase, which belongs to the family of carbonyl reductases, contributes to the enzymatic formation of PGF2 alpha in human brain.