title: The enzymatic conjugation of glutathione with bay-region diol-epoxides of benzo[a]pyrene, benz[a]anthracene and chrysene.
abstract: The kinetics of the enzymatic conjugation of glutathione (GSH) with the anti-diastereoisomers of trans-7,8-dihydroxy-9,10-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene (BPDE), trans-3,4-dihydroxy-1,2-epoxy-1,2,3, 4-tetrahydrobenz[a]anthracene (BADE) and trans-1,2- dihydroxy-3,4-epoxy-1,2,3,4-tetrahydrochrysene (CDE) catalyzed by transferase 4-4 from rat liver have been compared. When the concentration of these diol-epoxides was varied (using 2 mM GSH) the apparent Vmax values were 560, 2100 and 1500 nmol/mg/min for (+/-)-anti-BPDE, (+/-)-anti-BADE and (+/-)-anti-CDE, respectively, with corresponding apparent Km values of 11, 125 and 105 microM. The catalytic efficiency of transferase 4-4 in the GSH conjugation of (+/-)-anti-BADE and (+/-)-anti-CDE is thus approximately one-third of (+/-)-anti-BPDE (0.014 and 0.012 s-1 microM-1 respectively versus 0.042 s-1 microM-1). Similar non-linear Lineweaver-Burk plots were obtained with each diol-epoxide when the concentration of GSH was varied, and two apparent Km values of 0.02-0.04 and 0.4-0.9 mM GSH were estimated. The GSH-conjugates formed with the individual enantiomers of the racemic substrates used were resolved by h.p.l.c. The data indicate that with each diol-epoxide transferase 4-4 is highly selective (greater than or equal to 95%) towards the biologically most active (+)-enantiomer.
mesh_terms: D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide / Q000378:metabolism*; D000818:Animals; D001551:Benz(a)Anthracenes / Q000378:metabolism*; D001665:Binding Sites; D002911:Chrysenes / Q000378:metabolism*; D004101:Dihydroxydihydrobenzopyrenes / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D010616:Phenanthrenes / Q000378:metabolism*; D051381:Rats
chemical_list: D001551:Benz(a)Anthracenes; D002911:Chrysenes; D004101:Dihydroxydihydrobenzopyrenes; D010616:Phenanthrenes; D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; C026832:3,4-dihydroxy-1,2-epoxy-1,2,3,4-tetrahydrobenz(a)anthracene; C021977:chrysene,2-diol-3,4-epoxide-1; D005982:Glutathione Transferase; D005978:Glutathione