Release of rat liver endoplasmic reticulum membrane proteins into the cytosol

A membrane-free supernatant is prepared from rat liver cell homogenate by centrifugation at 230,000 x g. AMPase, NADH- and NADPH-cytochrome c reductase activities are demonstrated in the supernatant. These enzymes can be released from rough microsomal membranes by incubation in 0.25 M sucrose at 37 degrees C for 30 minutes. This release is time and temperature dependent and decreases in presence of phospholipase inhibitors. These results indicate that transfer of membrane enzymes from membranes to the cytosol may take place also in vivo. The process seems to be due to an enzymatic digestion of membranes and may be a mechanism for membrane turnover in addition to autophagocytosis.