The lipid metabolism of the marine brown alga D. membranacea was investigated using [2−14C]acetate, [1−14C]myristate, [l−I4C]oleate and [l−14C]arachidonate as precursors. On incubation with [2−14C]acetate, 18:1 and 16:0 were the main products formed by de novo synthesis and incorporated into polar lipids. With all the exogenous substrates used, DGTA was strongly labelled and the subsequent rapid turnover of radioactivity suggested a key role for this lipid in the redistribution of acyl chains and most likely also in the biosynthesis of the eukaryotic galacto-lipids produced in the absence of PC. In the glycolipids a continuous accumulation of radioactivity was observed with all the substrates used. The labelling kinetics of molecular species of MGDG suggested the desaturation of 18:1 to 18:4 and of 20:4 (n-6) to 20:5 (n−3) acids on this lipid. Both PG and PE were primary acceptors of de novo synthesized fatty acids and exogenous [l−14C]oleate, but no evidence exists for a further processing of acyl chains on these lipids. TAG, although strongly labelled with all exogenous [l−14CJacids, was not labelled when [2−14C]acetate was used as a precursor indicating the flux of endogenous fatty acids to be different of that of exogenously supplied fatty acid
