Reconstitution of the microsomal ethanol-oxidizing system. Qualitative and quantitative changes of cytochrome P-450 after chronic ethanol consumption.

Abstract

An ethanol-oxidizing system was reconstituted with cytochrome P-450, NADPH-cytochrome r reductase, and phospholipid.This system also metabolized propanol, butanol, and benzphetamine.Neither catalase nor alcohol dehydrogenase plays a role in this system.Characteristics of this system are similar to those of the microsomal ethanoloxidizing system.Chronic ethanol feeding of either male or female rats for 4 to 12 weeks resulted in significant quantitative and qualitative changes in hepatic cytochrome P-450.The absorption maximum of CO-difference spectrum of cytochrome P-450 shifted to higher wavelength.Three hemoproteins were resolved by continuous buffer sodium dodecyl sulfate-polyacrylamide gel electrophoresis of rat liver microsomes.Two of these increased after chronic ethanol feeding.One of these hemoproteins is distinct from those induced by phenobarbital or Y-methylcholanthrene treatment.On discontinuous buffer sodium dodecyl sulfate-polyacrylamide gel electrophoresis there was a preferential increase of two proteins with apparent molecular weights of 53,400 and 52,000, respectively.These two proteins probably represent the apoproteins of the two hemoproteins increased after chronic ethanol feeding.The partially purified cytochrome P-450 from ethanol-fed rats was more active for alcohol (ethanol, propanol, butanol) oxidation than the control preparation in the presence of excess NADPH-cytochrome c reductase and L-cY-dioleoyl lecithin.There was no significant difference in the capacity of partially purified NADPHcytochrome r reductase from either ethanol-fed rats or controls to promote alcohol oxidation in the presence of cytochrome P-450 and L-cu-dioleoyl lecithin.Thus, the adaptive increase of the microsomal ethanol-oxidizing system activity after chronic ethanol consumption can be attrib-