Glutathione conjugation of the carcinogenic and mutagenic electrophile (+/-)-7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-oxy-7,8,9,10-tetra hydrobenzo[a]pyrene catalyzed by purified rat liver glutathione transferases

Abstract

The kinetics of the enzyme-catalyzed conjugation of (+/-)-7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-oxy-7,8,9,10-tetrahydrobenzo[a]-pyrene [(+/-)-anti-BPDE] with glutathione (GSH) by the following purified soluble rat liver GSH transferases: 1-1, 1-2, 2-2, 3-3, 3-4 and 4-4 have been studied. When BPDE concentration was varied while GSH concentration remained constant (1 mM), linear Lineweaver-Burk plots were obtained: maximum rates of conjugation mediated by GSH transferases 1-1, 1-2, 2-2, 3-3, 3-4 and 4-4 were 105, 72, 83, 35, 179 and 357 nmol/min/mg protein, respectively. When GSH concentration was varied while BPDE concentration remained constant (40 microM), biphasic Lineweaver-Burk plots were obtained in each case with a break point of 0.2 mM GSH below which the affinity of these enzymes for GSH was apparently greater. These results are discussed with respect to the detoxication of benzo[a]pyrene (BP) in vivo.