title: Effects of molecular substitution patterns on the cytochrome P-450-dependent metabolism of 2,2',3,5,5',6- and 2,2',3,4,4',6-hexachlorobiphenyl by rat liver microsomal monooxygenases.
abstract: The metabolism by rat hepatic microsomal cytochrome P-450-dependent monooxygenases of several model substrates that are specific for individual isoforms of cytochrome P-450 and the metabolism by these monooxygenases of two structurally related isomers of hexachlorobiphenyl was studied. The most striking result was that 2,2',3,5,5',6-hexachlorobiphenyl was metabolised in vitro at the rate of 4.5 pmol/mg microsomal protein per min, whereas the other isomer 2,2',3,4,4',6-hexachlorobiphenyl was not metabolised at detectable rates. This finding provides strong evidence for a regioselective oxidative attack by cytochrome P-450-dependent monooxygenase with preferential insertion of oxygen at meta-para unsubstituted carbon atoms. Investigations into the mechanism of this oxidative attack suggest that the ortho hydrogen atom at carbon atom C-6' of 2,2',3,4,4',6-hexachlorobiphenyl was associated with a lower charge (0.075 e) compared with the meta or para hydrogen atoms at carbon atom C-3' and C-4' of 2,2',3,5,5',6-hexachlorobiphenyl (0.086 e). In addition, measurement of the main C-C bond length using MOPAC calculations and X-ray crystalographic data suggests significant differences in the bond-length distance, with the main bond lengths of 1.390, 1.385 and 1.374 A, respectively, for bridgehead to ortho (C1-C2), for ortho to meta (C2-C3), and for meta to para bonds. These results provide evidence that the preferential meta-para oxidative attack is linked to a shorter carbon-carbon bond length and a more positive charge distribution of the corresponding hydrogen atoms.
authors: Department of Biochemistry and Physiology, University of Reading, U.K.
authors: J T
authors: JT
authors: Borlakoglu
authors: M G
authors: MG
authors: Drew
authors: J P
authors: JP
authors: Wilkins
authors: R R
authors: RR
authors: Dils
mesh_terms: D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry* / Q000378:metabolism; D005260:Female; D007536:Isomerism; D008862:Microsomes, Liver / Q000201:enzymology*; D010100:Oxygen / Q000378:metabolism; D010105:Oxygenases / Q000737:chemistry* / Q000378:metabolism; D011078:Polychlorinated Biphenyls / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013379:Substrate Specificity; D014961:X-Ray Diffraction
chemical_list: C066675:2,2',3,5,5',6-hexachlorobiphenyl; C059158:2,2',3,4,4',6-hexachlorobiphenyl; D003577:Cytochrome P-450 Enzyme System; D011078:Polychlorinated Biphenyls; D010105:Oxygenases; D010100:Oxygen