Molecular Pharmacology, Vol 7, 26-32, Copyright © 1971 by the American Society for Pharmacology and Experimental Therapeutics

Effects of Extraction with Isooctane upon the Properties of Liver Microsomes

¹ Department of Pharmacology and Therapeutics, University of Florida Medical School, Gainesville, Florida 32601, and Department of Biochemistry, University of Texas Southwestern Medical School, Dallas, Texas 75235

When rat liver microsomes were extracted with isooctane (2,2,4-trimethylpentane), the resultant preparation was essentially devoid of the ability to produce a type I difference spectrum upon addition of hexobarbital. At high concentrations of hexobarbital, a type II spectral change was obtained with the extracted microsomes. The type II interaction of aniline with isooctane-extracted microsomes was not enhanced in the presence of hexobarbital, as it was in the case of untreated microsomes. Hexobarbital binding to cytochrome P-450 of untreated microsomes was inhibited in the presence of isooctane, but the amount of residual isooctane in the extracted microsomes was not sufficient to explain the loss of hexobarbital-binding activity. The isooctane extracts contained phosphatidylcholine and phosphatidylethanolamine. The results are discussed in terms of a model in which the type I binding form of cytochrome P-450 involves an association of hemoprotein with a phospholipid, or with some other microsomal constituent in an interaction involving phosphatides.