Positional distribution of octadecadienoic acids in sponge phosphatidylethanolamines

The distribution of C14-C22 fatty acids in the phosphatidylethanolamines isolated from the sponges Agelas sp. and Spongia tampa was investigated. Selective changes with phospholipase A2 (from Agkistrodon 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 position sn-1 or sn-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 positions sn-1 and sn-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 the sn-2 position.