Phospholipids

Abstract

Phospholipids (PL) are amphiphilic molecules with lipophilic acyl chains and a hydrophilic head. Gene-rally, two main types of phospholipids can be found in living tissues. A first group, the glycerophospholipids, consist of a glycerol backbone with two fatty acids esterified at position sn-1 or sn-2. On the third hydroxyl, a phosphate residue is bound on to which different organic bases or other complex organic groups may be linked.Generally, the fatty acid chain on the sn-1 position is more saturated compared to the one at the sn-2 position on the glycerol moiety. Lysophospholipids (LPC, LPE, etc.) contain only one acyl group, which is predominantly esterified at the sn-1 position. Apart from diacyl forms, some phospholipid species from animal and microbial origin have an ether or vinyl ether linkage at the sn-1 position, and are denoted as alkylacyl-and alkenylacyl-glycerophospholipids, respectively. The latter form is also known as plasma-logen. The polar organicbase on the phosphate determines the type of phospholipid. Phosphatidic acid (PA) is an important intermediate in the biosynthesis of triglycerides and phospholipids; however, it is only present in very small amounts in living tissue.The concentration of this acidic phospholipid is often overestimated due to enzymatic hydrolysis of other phospholipids by phospholipase D. Phosphatidylgly-cerol (PG) is present in the mitochondria of bacteria and in chloroplasts of plants. In animal tissues it serves.