5 - The Biosynthesis of Unsaturated Fatty Acids

Abstract

This chapter discusses the biosynthesis of unsaturated fatty acids. All organisms, with the exception of anaerobic bacteria, form unsaturated fatty acids by direct introduction of a double bond into the hydrocarbon chain of a preformed fatty acid, whether it be saturated, monounsaturated, or polyunsaturated. Other types of fatty acids may arise by subsequent chain elongation, but most of the evidence to date suggests that the mechanism of the dehydrogenation itself is identical whether the organism be a higher or lower animal, or higher or lower plant. Differences exist only in cofactor requirements, specificity of double bond position, and possibly, though this is less certain, differences in the form of the substrate. Except for bacteria, all organisms are capable of introducing more than one double bond into the chain. These double bonds are always separated by a methylene group and are known as methylene-interrupted polyunsaturated fatty acids. The emphasis is rather on the unity of mechanism and the economy of enzymic species by which the vast array of naturally occurring unsaturated fatty acid molecules are produced.