ISOLATION AND CHARACTERIZATION OF A NEW PHOSPHOLIPID FROM BROWN-ALGAE- INTRACELLULAR-LOCALIZATION AND SITE OF BIOSYNTHESIS

In various orders of brown algae a novel lipid constituent PX was dete cted and suggested to be a phosphoglyceride bearing an amino-containin g polar head group. We discuss its tentative structure based on IR, NM R, MS and chemical data. PX accounted for 2-4% of total lipids and alw ays exhibited a fatty acid composition rich in 20:4 (arachidonic) and 20:5 (eicosapentaenoic) acids. High proportions of these long-chain po lyunsaturated acids implied a predominantly cytoplasmic biosynthesis o f its diglyceride part. In Ectocarpus siliculosus (Phaeophyceae) PE ha s a fatty acid pattern similar to PX. In its gametes PX accumulates in the plasma membrane and, in addition, shows a characteristic sex-spec ific composition of its acyl moieties. In female plasma membranes the content of 20:5 acid is significantly higher than in male plasma membr anes or whole plants. This is possibly due to 20:5 acid from PX acting as a direct precursor for pheromone biosynthesis. PX is suggested to be of special physiological importance in terms of an acyl donor in th is process. The 20:5 pool in PX was estimated to be sufficient to synt hesize 70% of the pheromone ectocarpene.