Ether phospholipids are lipids containing an alkyl group, rather than an acyl group, linked to one of the oxygen atoms of glycerol (see here). Metabolic pathways leading to ether phospholipids are shown in Figure 19.11 and Figure 19.12.
Plasmalogens (vinyl ethers) are phospholipids containing an alkenyl ether at position sn-1 of glycerol. They are synthesized in peroxisomes (Figure 19.12) and constitute 50% of all choline phospholipids in heart tissue. Nevertheless, they are virtually undetectable elsewhere in the body. Individuals deficient in plasmalogen synthesis (such as those with Zellweger syndrome) suffer damage to brain, liver, and kidney before reaching an early death.
Platelet-activating factor (structure) is a glycerol ether with potent physiological properties. At concentrations as low as 1 picomolar, it stimulates of blood platelet aggregation, reduction of blood pressure, activation of several white blood cell classes, decreased cardiac output, glycogenolysis, uterine contraction.
Ether phospholipids are abundant in halophilic ("salt loving") microorganisms. These are bacteria and protozoa that grow in media with NaCl concentrations as high as 4M. The stability of alkyl ethers against hydrolysis, compared to acyl esters, may be the reason.