A unique phospholipid organization in bovine erythrocyte membranes

Ruminant erythrocytes are remarkable for their choline-phospholipid anomali es; namely, low or absent phosphatidylcholine (PC) along with high sphingom yelin levels. Here, we report another anomaly in bovine erythrocytes that a ffects aminophospholipids: phosphatidylethanolamine (PE) shows an extreme a symmetry, with only 2% of the total present in the outer leaflet. Furthermo re, we found that phospholipase A(2), an enzyme located on the external sur f ace of the erythrocytes, shows higher activity against PC than against PE . In addition, we observed that acylation of PE is by far the most importan t biosynthetic event in this system. We propose that deacylation of PE and PC by phospholipase A2 to generate lysocompounds, followed by selective rea cylation of lyso-PE in the inner leaflet, can account for the compositional and architectural peculiarities of bovine erythrocyte membranes.