Density gradient fractionation of digitonin-treated rat liver plasma membranes and subcellular localization of NADH-oxidoreductase and B-type cytochromes.

Plasma membranes, contaminated very little by endoplasmic reticulum elements, were isolated from rat liver. Activities of NADH-oxidoreductase and b-type cytochromes were higher than expected from this contamination. Between 50 and 80% of these activities were endogenous to plasma membrane. A similar result was obtained after refractionation of digitonin-treated plasma membranes on a sucrose density gradient. This is further evidence for the localization of NADH-ferricyanide reductase, NADH-cytochrome c reductase, and cytochromes b5, P450 and P420 in liver cell membranes.