Nuclear membranes and plasma membranes from hen erythrocytes. 3. Localization of activities incorporating fatty acids into phospholipids.

Nuclear membranes and plasma membranes isolated from mature hen erythrocytes differ widely in their phospholipid, cholesterol, and cholesterol ester composition. The plasma membranes contain relatively high amounts of sphingomyelin and cholesterol, as is known for plasma membranes from other cell types. The molar ratios of cholesterol to phospholipid are 1.04 for plasma membranes and 0.42 for nuclear membranes, whereas the molar ratios of cholesterol to sphingomyelin are nearly identical to both membranes (3.39 and 3.23, respectively). Appreciable amounts of alk-1-enyl-acyl and alkyl-acyl analogues of phosphoglycerides are present in both membranes. The individual phosphoglycerides show distinct patterns of ether analogues. The proportion of ether analogues is not different in nuclear membranes and plasma membranes. Similar characteristics are found in the fatty acid residues of the phosphoglycerides. Quantitative evaluation of the lipid data for whole cells, nuclear membranes, and plasma membranes is in correspondence with the 1: 1 surface ratio of both membrane classes in this cell.