ABSTRACT
Biological membranes contain a large variety of lipid groups, variants within each group, and different molecular species within each class. The phospholipid composition of other rat organs does not differ drastically from that of the liver. Phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and sphingomyelin account for about 90% of the total rat liver phospholipids. The phospholipid composition of nuclear membranes is very similar to that of the endoplasmic reticulum and, in agreement with their endocytic origin, secondary lysosomes have a phospholipid composition similar to that of plasma membranes. In addition to this specific localization of certain phospholipids in a given membrane fraction, it is important to note that plasma membranes contain most of the cellular glycolipids and cholesterol. In addition to the differences in fatty acid composition between the various glycophospholipid classes, there are also marked differences among the different subclasses for a given glycophospholipid.
