Positional distribution of octadecadienoic acids in sponge phosphatidylethanolamines

The distribution of C14–C22 fatty acids in the phosphatidylethanolamines isolated from the spongesAgelas sp. andSpongia tampa was investigated. Selective changes with phospholipase A₂ (fromAgkistrodon halys blomhoffii) followed by thin-layer chromatographic separation of the resulting lysophosphatidylethanolamines and free fatty acids and subsequent methylation with HCl/MeOH and diazomethane, respectively, revealed that the 5,9-octadecadienoic acid and the 9,12-octadecadienoic acid present showed no preference for either positionsn-1 orsn-2 in these phosphatidylethanolamines. The other saturated and unsaturated fatty acids with chains between 14 and 22 carbons long were also found to be equally distributed between positionssn-1 andsn-2 in the phosphatidylethanolamines in these sponges. The results contrast with what is known about the distribution in most mammalian phospholipids, such as the phosphatidylcholines from human erythrocytes, where octadecadienoic acid typically occupies thesn-2 position.