Biosynthetic studies of marine lipids. 17. The course of chain elongation and desaturation in long-chain fatty acids of marine sponges

Through appropriate labeling and incorporation experiments, the biosynthesis of the most characteristic sponge fatty acids, (5Z,9Z)-5,9-hexacosadienoic acid ( Delta super(5,9)-26:2) and (5Z,9Z,19Z)-5,9,19-hexacosatrienoic acid ( Delta super(5,9,19)-26:3), was completely elucidated. The dienoic acid is produced by the sequence 14:0 arrow right arrow right 26:0 arrow right 26:1 arrow right 26:2. Contrary to precedent in animal fatty acid biosynthesis, the first desaturation occurs both at Delta super(5) and Delta super(9). The sponge secures palmitoleic acid ( Delta super(9)-16:1) from an exogenous source (bacteria?) and undergoes chain elongation to Delta super(19)-26:1 before undergoing Delta super(9)- and Delta super(5)-desaturation.