Requirement for Reduced Diphosphopyridine Nucleotide-Cytochrome b5 Reductase in Stearyl Coenzyme A Desaturation

Abstract

Abstract The stearyl coenzyme A desaturase system of hen liver microsomes has been purified 4-fold by fractionation with deoxycholate. Further fractionation by diethylaminoethyl cellulose column chromatography has yielded a particle (DE fraction) in which DPNH-cytochrome c reductase activity has been enriched 10-fold but desaturase activity has been completely lost. Treatment of the purified desaturase with N-ethylmaleimide has yielded a particle (N fraction) with neither desaturase nor DPNH-cytochrome c reductase activity present. Combination of the N fraction with the DE fraction has restored the stearyl-CoA desaturase activity. The DE fraction can be completely replaced by the soluble, highly purified DPNH-cytochrome b5 reductase. These observations strongly suggest that DPNH-cytochrome b5 reductase is an integral part of the stearyl-CoA desaturase system.