Lipid Organization in Biological Membranes

Abstract

Extensive studies on the lipid composition of many biological membranes have revealed that each membrane contains a, more or less specific, wide collection of different lipid species. Variations are found both in the polar head group and the apolar side chains of the lipids. If one considers only the phospholipids, more than 400 different species can be found in nature (Fig.1). An example of the diversity in lipid composition of membranes from various origins is given in Table 1. The human erythrocyte membrane is characterized by its high content of sphingomyelin, phosphatidylcholine, and phosphatidylethanolamine and furthermore by a substantial amount of unsaturated fatty acids that are predominantly esterified to the C-2 position of the phospholipids (for a review see Ref. 1). The major phospholipid in Escherichia coli is phosphatidylethanolamine, containing considerable amounts of cyclopropane fatty acids (2). The third organism that will be discussed in this paper is Acholeplasma laidlawii. The plasma membrane of this organism contains only one diacylglycero-3-phosphate derivative: phosphatidyl- glycerol, which amounts for 30% of the total membrane lipid content. All other lipids are glucosylated derivatives of diglycerides.