STEREOSELECTIVE CONJUGATION OF PROSTAGLANDIN A(2) AND PROSTAGLANDIN J(2) WITH GLUTATHIONE, CATALYZED BY THE HUMAN GLUTATHIONE S-TRANSFERASES A1-1, A2-2, M1A-1A, AND P1-1

Prostaglandins containing an alpha,beta-unsaturated keto group, such a s prostaglandin A(2) (PGA(2)) and prostaglandin J(2) (PGJ(2)), inhibit cell proliferation. These cyclopentenone prostaglandins may be conjug ated with GSH chemically or enzymatically via glutathione S-transferas es, and this has been suggested to result in inhibition of the antipro liferative mode of action. In the present study, the role of the major human GSTs in the conjugation of PGA(2) and PGJ(2) with GSH was inves tigated with purified enzymes, i.e., the Alpha-class enzymes GST A1-1 and GST A2-2, the Mu-class enzyme GST M1a-1a, and the Pi-class enzyme GST P1-1. The GSH conjugates were separated from the parent compound b y HPLC and identified by fast atom bombardment mass spectrometry and H -1-NMR. Two GSH conjugates were found for both PGA(2) and PGJ(2), the R- and S-GSH conjugates of both prostaglandins. Incubation experiments with PGA(2) and PGJ(2) (70-600 mu M) clearly showed the role of indiv idual GSTs in the conjugation of PGA(2) and PGJ(2). Compared to the ch emical reaction, enzyme activities towards PGA(2) were up to 5.4 times as high (GSTA1-1) at the lowest concentration (70 mu M), while at the highest concentration (600 mu M) enzyme activities were up to 3.0 tim es as high (GST P1-1). For PGJ(2), enzyme activities were Up to 4.3 (G STM1a-1a, 70 mu M) and up to 3.1 (GSTM1a-1a, 600 mu M) times as high. As expected, similar amounts of the R- and S-conjugates of both prosta glandins were found in the chemical reaction. Striking stereoselectivi ties in conjugating activities were observed for GST A1-1 and GST P1-1 . GST A1-1 favors the formation of the R-GSH conjugates of both prosta glandins. GST P1-1 showed a clear selectivity with regard to the forma tion of the S-GSH conjugate of PGA(2). However, this selectivity was n ot found for the formation of the S-GSH conjugate of PGJ(2). GSTM1a-1a showed no stereoselectivity with regard to the GSH conjugation of bot h PGA(2) and PGJ(2). GSTA2-2 only showed some minor formation of the R -GSH conjugate of PGJ(2). The possible implications of the observed st ereoselectivity on the effects of PGA(2) and PGJ(2) are discussed.