REDUCTION OF PROSTAGLANDIN D-2 TO 9-ALPHA,11-BETA-PROSTAGLANDIN F2 BY A HUMAN LIVER 3-ALPHA-HYDROXYSTEROID DIHYDRODIOL DEHYDROGENASE ISOZYME

Prostaglandin (PG) specificity of two 3 alpha-hydroxysteroid/dihydrodiol dehydrogenase isozymes, DD2 and DD4, of human liver was examined. DD2 exhibited NADPH-linked reductase activity for 9-,11- and 15-ketoprostaglandins at a pH optimum of 6.0, whereas DD4 reduced only 15-ketoprostaglandin F-2 alpha. DD2 showed the highest V-max/K-m value for PGD(2) of the PG substrates, and the reduced product of PGD(2) was identified to 9 alpha,11 beta-PGF(2) by gas chromatography-mass spectrometry. In the reverse reaction with NADP(+) as a cofactor, the two enzymes slowly oxidized several PGs with 9-, 11- and/or 15-hydroxy groups, except that DD2 showed high activity for 9 alpha,11 beta-PGF(2) at a pH optimum of 10.0. The K-m and V-max values of DD2 for PGD(2) were 57 mu M and 250 nmol/min per mg, respectively, at pH 7.0 and 37 degrees C, and the respective values for 9 alpha,11 beta-PGF(2) were 72 mu M and 10 Mmol/min per mg. PGD(2) 11-ketoreductase activity in human liver cytosol was recovered in 30-75% saturated ammonium sulfate fraction. More than 77% of the PGD, 11-ketoreductase activity in the ammonium sulfate fraction was immunoprecipitated by antibodies against DD2, and inhibited by known inhibitors of the enzyme. These results suggest that DD2 is a major soluble PGD(2), 11-ketoreductase species in human liver.