Abstract
Treatment of rat liver microsomes with cathepsin D [EC 3. 4. 4. 23] resulted in the selective solubilization of NADH-cytochrome b5 reductase [EC 1. 6. 2. 2.], leaving other electron transferring components such as cytochrome b5, NADPH-cytochrome c re-ductase [EC 1. 6. 2. 4] and cytochrome P-450 still attached to the membrane. The rate and the extent of reduction of membrane-bound cytochrome b5 by NADH were studied with digested microsomal samples containing different amounts of the cyto-chrome b5 reductase. The analysis of the reduction kinetics of the cytochrome b5 suggested the presence of the assemblies of cytochrome b5 and its reductase in the original microsomal membrane. An assembly seems to contain about five molecules of NADH cytochrome b5 reductase and about fifty molecules of cytochrome bs gath-ered togather in the membrane.
