Glutathione conjugation of the carcinogenic and mutagenic electrophile (±)-7β,8α-dihydroxy-9α,10α-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 (±)-7β,8α-dihydroxy-9α,10α-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 μM), 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.