Phospholipid class and fatty acid composition of golgi apparatus isolated from rat liver and comparison with other cell fractions.

Rough endoplasmic reticulum, Golgi apparatus, and plasma membrane rich cell fractions were isolated from livers of rats under similar conditions of age and diet for analysis of phospholipid classes and fatty acid composition. Phosphatidylcholine was the major phospholipid of all membrane types. Golgi apparatus was intermediate between endoplasmic reticulum and plasma membrane with respect to levels of phosphatidylcholine and sphingomyelin. Endoplasmic reticulum was highest in phosphatidylcholine and lowest in sphingomyelin. Levels of lysophosphatidylcholine, phosphatidylserine, phosphatidylinositol, and phosphatidylethanolamine were relatively constant comparing endoplasmic reticulum, Golgi apparatus, and plasma membrane. Lysophosphatidylethanolamine was detected in Golgi apparatus and plasma membrane but not in endoplasmic reticulum. Neutral lipids represented 15 x of the total extractable lipids of endoplasmic reticulum, 38 of the total extractable lipids of plasma membrane, and 46 x of the total extractable lipids of Golgi apparatus. Neutral lipid fractions were composed mainly of cholesterol, free fatty acids, and triglycerides with P recise knowledge on the composition of components comprising the cytoplasmic membrane system of mammalian cells (nuclear envelope, endoplasmic reticulum, Golgi apparatus, secretory vesicles, and plasma membranes) is limited. However, during the last decade development of suitable methods for isolation have permitted detailed characterization of lipids from rat liver plasma membranes (Emmelot et al., 1964; Takeuchi an;d Terayama, 1965; Skipski et al., 1965; Ashworth and Green, 1966; Dod and Grey, 1968; Pfleger et al., 1968) and rough endoplasmic reticulum membranes (Dallner et al., 1966; Glauman and Dallner, 1968). More recently, methods for the reproducible isolation of a highly purified Golgi apparatus fraction of useful quantity have become available (MorrC et al., 1969b), and it is now possible to make detailed comparisons of the lipid composition of Golgi apparatus with those of rough endoplasmic reticulum and plasma membranes as a first step in relating morphological differences among these cell components (Sjostrand, 1963,1968) to differences in membrane constituents. Such comparisons are of importance not only in view of the essential role played by lipids in the structure and function of membranes (Green and Tzagoloff, 1966) but also from the standpoint of clarification of the pro-