title: Reduction of benzyl halides by liver microsomes. Formation of 478 NM-absorbing sigma-alkyl-ferric cytochrome P-450 complexes.
abstract: The benzyl halides benzyl bromide and 4-nitrobenzyl chloride are reduced anaerobically by NADPH and rat liver microsomes to yield toluene and 4-nitrotoluene, respectively. These reductions and cytochrome P-450-dependent since they are inhibited by CO and metyrapone, and are increased after pretreatment of rats by phenobarbital and 3-methylcholanthrene. During benzyl halide reduction, cytochrome P-450 complexes, which are very unstable to O2 and characterized by a Soret peak at 478 nm, are formed in steady-state concentrations. These concentrations are very dependent on pretreatment of rats and on the nature of the reducing agent (NADPH or dithionite) and the benzyl halide:4-methylbenzyl bromide and benzyl bromide lead to 478 nm absorbing complexes in the presence of NADPH whereas 4-nitrobenzyl chloride and benzyl chloride lead to such completes only in the presence of dithionite. Microsomal reductions of 4-nitrobenzyl chloride and benzyl bromide in D2O lead to partially deuterated 4-nitrotoluene and toluene. From these results, we propose a mechanism for anaerobic microsomal reduction of benzyl halides involving the intermediate formation of sigma-alkyl cytochrome P-450-Fe(III)-CH2Ar complexes which exhibit red-shifted Soret peaks around 478 nm. Toluenes, ArCH3, are formed either by protonation of the sigma-alkyl complexes or by hydrogen abstraction by the intermediate free radical ArCH2.
mesh_terms: D000818:Animals; D001593:Benzyl Compounds / Q000378:metabolism; D002849:Chromatography, Gas; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D006846:Hydrocarbons, Halogenated / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D009578:Nitrobenzenes / Q000378:metabolism; D010084:Oxidation-Reduction; D051381:Rats; D011919:Rats, Inbred Strains; D013053:Spectrophotometry; D013056:Spectrophotometry, Ultraviolet
chemical_list: D001593:Benzyl Compounds; D006846:Hydrocarbons, Halogenated; D009578:Nitrobenzenes; C027562:4-nitrobenzyl chloride; D009249:NADP; D003577:Cytochrome P-450 Enzyme System; C038682:benzyl bromide