Biosynthetic studies of the polar lipids of Halobacterium cutirubrum. Formation of isoprenyl ether intermediates

Abstract Biosynthetic studies were carried out on the complex polar lipids of the extreme halophile, Halobacterium cutirubrum . Cells were pulse-labeled with [ 32 P]phosphate, [ 14 C]mevalonate and [ 14 Clglycerol for short terms (1, 15, 30, 60 min); incorporation of radiolabels into total lipids and their distribution among individual lipid components were determined as a function of incubation time. Glycerol was incorporated 9-fold more rapidly into total lipids than mevalonate, but at the same rate as phosphate. Several intermediate components were detected by short-term (1–30 min) pulse labeling, some of which were shown to be allyl ether-bound isoprenyl intermediates of the major saturated diphytanylglycerol ether lipids, phosphatidylglycerophosphate (PGP), phosphatidylglycerol (PG), phosphatidylglycerosulfate (PGS) and sulfated triglycosyldiphytanyl-glycerol (S-TGD). These intermediate components were detected by their products of acid methanolysis, alkaline hydrolysis and Vitride reduction, before and after catalytic hydrogenation. Another intermediate detected was the isoprenyl ether analogue of phosphatidic acid, which showed a product-precursor relationship with PGP and PG for all three radioisotope precursors. Other intermediates remain unidentified, but their product-precursor relationship was established by their labeling patterns with the three radioisotope precursors. These studies suggest that the biosynthetic pathways for the major diphytanylglycerol ether phospho- and glycolipids involve formation of the respective isoprenyl intermediates that are reduced in a stepwise fashion to the fully saturated diphytanylglycerol ether phospho- and glycolipids. Chase studies, following a 24 h labeling period, showed that the major phospholipid (PGP) has a very low turnover rate for phosphate groups, but a 3-fold higher turnover of the phytanyl groups; the minor phospholipids PG and PGS have much higher phosphate turnover rates.