Chapter 9 Ether-linked lipids and their bioactive species

Abstract

Ether-linked lipids occur throughout the animal kingdom and are even found as minor components in several higher plants. This chapter describes the historical highlights of ether-linked lipids, their natural occurrence, their physical properties, biologically active ether lipids, enzymes involved in ether lipid synthesis, catabolic enzymes, their metabolic regulation, and their functions. Ether linkages in the phospholipids of mammalian cells exist almost exclusively in the choline and ethanolamine glycerolipid classes, except for intermediary metabolites and certain bioactive lipids. Ether-linked lipids have been shown to decrease ion permeability, surface potential, and lower the phase temperature of membrane bilayers, when compared to their diacyl counterparts. The chapter also describes enzymes involved in ether lipid synthesis, such as acyl-coenzyme A (CoA) reductase, and dihydroxyacetone-P acyltransferase. Invasive cells, such as neutrophils and eosinophils have high levels of ether lipids, and the organisms living in harsh environments of high temperatures or high salt and low pH contain only ether lipids suggesting that they serve as the Teflon of lipids. However, there are many unanswered questions about the dual role that ether lipids serve as membrane components and as cellular signaling molecules, such as the biosynthesis of choline plasmalogens, is still not fully understood.