Isolation and characterization of a new phospholipid from brown algae. Intracellular localization and site of biosynthesis

Summary In various orders of brown algae a novel lipid constituent PX was detected and suggested to be a phosphoglyceride bearing an amino-containing polar head group. We discuss its tentative structure based on IR, NMR, MS and chemical data. PX accounted for 2–4% of total lipids and always exhibited a fatty acid composition rich in 20:4 (arachidonic) and 20:5 (eicosapentaenoic) acids. High proportions of these long-chain polyunsaturated acids implied a predominantly cytoplasmic biosynthesis of its diglyceride part. In Ectocarpus siliculosus (Phaeophyceae) PE has a fatty acid pattern similar to PX. In its gametes PX accumulates in the plasma membrane and, in addition, shows a characteristic sex-specific composition of its acyl moieties. In female plasma membranes the content of 20:5 acid is significantly higher than in male plasma membranes 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 this process. The 20:5 pool in PX was estimated to be sufficient to synthesize 70% of the pheromone ectocarpene.