Long and Very Long Polyunsaturated Fatty Acids of Retina and Spermatozoa: The Whole Complement of Polyenoic Fatty Acid Series

Abstract

Photoreceptor cells and spermatozoa have long been known to be the richest sources of polyunsaturated fatty acids (PUFA) in vertebrates. Docosahexaenoate (22:6n-3) and docosapentaenoate (22:5n-6), according to species and in diverse proportions, are common major acyl chains of the glycerophospholipids of these highly specialized cells. Both 22:6n-3 and 22:5n-6 are the products of a reaction that involves the introduction of a double bond in theΔ4 position of the chain in 22:5n-3 and 22:4n-6 respectively. Even though this reaction has yet to be fully characterized, the most highly unsaturated fatty acids that occur in vertebrate membranes are known to result from such desaturation. The four fatty acids just mentioned and their predecessors are grouped into two“lineages,”defined by the position of the first double bond counting from the methyl end, as the n-3 and the n-6 families. However, each of the four can be elongated, thus producing four lines of descendants, each line comprising various n-3 hexaenoic, n-6 pentaenoic, n-3 pentaenoic, and n-6 tetraenoic PUFA respectively. This chapter summarizes our findings on retina, joining them with more recent ones on spermatozoa, PUFA components, and the peculiar glycerophospholipids in which they occur. It is shown that, just as the glycerophospholipids of retina contribute to extend our view of existing PUFA by disclosing a whole variety of chain lengths within each of the known PUFA“lineages,”the glycerophospholipids of spermatozoa do so by disclosing new lineages for each of the known PUFA lengths. Intricate as this may sound, this overview expands, but at the same time simplifies, our picture of PUFA structural and metabolic relationships.