Cell membrane localization of long chain C24?C30 fatty acids in two marine demosponges

Subcellular fractionation by differential centrifugation was performed on two previously unstudied marine sponges (Reniera sp. andPseudaxinyssa sp.) that represent both major subclasses of the Demospongiae. Long chain fatty acids (LCFA) with 24–30 carbon units were found as major constituents of cell membrane isolates of both sponges. Most LCFA were polyunsaturated and were constituents of the phospholipids, which are typical membrane lipids, and in particular the amino-phospholipids. The LCFA composition of phospholipids from whole sponge tissue was shown to provide a reliable indication of the LCFA composition of cell membrane phospholipids in the sponges studied. An unusual triply branched C₁₆ isoprenoid fatty acid, 4,8,12-trimethyltridecanoic acid, also was identified as a cell membrane acid in the spongePseudaxinyssa sp. Part 16 of “Phospholipid Studies of Marine Organisms.” For Part 15 in this series see Dasgupta, A., Ayanoglu, E., Tomer, K.B., and Djerassi, C. (1987)Chem. Phys. Lipids 43, 101–111.