Transbilayer distribution of phospholipid synthesizing enzymes in the sarcoplasmic reticulum membrane

Abstract

The topology of enzymes involved in phospholipid synthesis in the membrane of sarcoplasmic reticulum vesicles was investigated by means of limited proteolysis. The digestion of sarcoplasmic reticulum proteins with different proteases caused the considerable decrease of the activities of choline- and ethanolaminephosphotransferases without significant inactivation of glycerophosphate and lysophosphatidylcholine acyltransferases. On the basis of these results we concluded that the active sites of phosphotransferases are located on the cytoplasmic side, whereas the active sites of acyltransferase are present either on the extracytoplasmic side or burried into the sarcoplasmic reticulum membrane.