Phospholipids typical total composition

The correct ratio of lipid constituents is important to form stable liposomes. For instance, a reliable liposomal composition for encapsulating aqueous substances may contain molar ratios of lecithin cholesterol negatively charged phospholipid (e.g., phosphatidyl glycerol (PG)) of 0.9 1 0.1. A composition that is typical when an activated phosphatidylethanolamine (PE) derivative is included may contain molar ratios of phosphatidylcholine (PC) cholesterol PG derivatized PE of 8 10 1 1. Another typical composition using a maleimide derivative of PE without PG is PC male-imide-PE cholesterol of 85 15 50 (Friede et al., 1993). In general, to maintain membrane stability, the PE derivative should not exceed a concentration ratio of about l-10mol PE per lOOmol of total lipid. 

Thus, the fat globules are surrounded, at least initially, by a membrane typical of eukaryotic cells. Membranes are a conspicuous feature of all cells and may represent 80% of the dry weight of some cells. They serve as barriers separating aqueous compartments with different solute composition and as the structural base on which many enzymes and transport systems are located. Although there is considerable variation, the typical composition of membranes is about 40% lipid and 60% protein. The lipids are mostly polar (nearly all the polar lipids in cells are located in the membranes), principally phospholipids and cholesterol in varying proportions. Membranes contain several proteins, perhaps up to 100 in complex membranes. Some of the proteins, referred to as extrinsic or peripheral, are loosely attached to the membrane surface and are easily removed by mild extraction procedures. The intrinsic or integral proteins, about 70% of the total protein, are tightly bound to the lipid portion and are removed only by severe treatment, e.g. by SDS or urea. 

All eukaryotic and prokaryotic cell membranes contain PS and PE. In mammalian cells PE is typically the second most abundant phospholipid, comprising -20% of total phospholipids. Different organelles — plasma membrane, ER, lysosomes, and mitochondria — have distinct phospholipid compositions. The PE content of mitochondria is higher than... 

A typical fish polar lipid fraction contains about 60% phosphatidylcholine (PC), 20% phosphatidylethanolamine (PE), and several percent phosphatidylserine and sphingomyelin, while the remainder is composed of other minor phospholipids, hi fish, the phospholipid PC PE ratio is generally 2-3 1. The PC PE ratio in phospholipids of bream, a freshwater fish (total lipid content of 4 to 6% w/w), was as low as 1.3 to 1.9 1 (Kolakowska et al., 1993, 2000a). A PC PE ratio of approximately 2 1 was recorded in phospholipids of the light and dark muscle of trout (Ingemansson et al., 1991). Various cod tissues were found to differ in their phospholipid composition. The PC PE ratios of white and dark muscle of the cod were 3.5 1 and 2.7 1, respectively (Lie and Lambertsen, 1991b). Invertebrate phospholipids contain less PC than those from vertebrates. As shown by a study conducted over two annual... 

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