chapter  12
Pages 34

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 phos-

phate 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 organic base on the phosphate

determines the type of phospholipid. Phosphatidic

acid (PA) is an important intermediate in the biosynth-

esis 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