The major polar lipids identified in Halobacterium cutirubrum and other extreme halophiles are the diphytanyl ether analogues of phosphatidyl glycerophosphate and phosphatidyl glycerol, and a glycolipid sulfate esterl,e). A minor unidentified polar component, labelled both with 3Zp and 3sS, has also been detectedl-a). We report here structural studies leading to the identification of this phosphosulfolipid as a sulfate ester of the diphytanyl ether analogue of phosphatidyl glycerol.
The chromatographically pure phosphosulfolipid was isolated from the acetone-insoluble lipids of H. cutirubrum 4, 5) by preparative thin-layer chromatography on plates of silica gel H using the solvent system chloroform-methanol-30% ammonium hydroxide (65: 35 : 5, v/v) 5). The product was a white hygroscopic powder, accounting for approximately 4% by weight of the total acetone-insoluble (polar) lipids. It gave a single spot on TLC with R 1 0.62, 0.37, and 0.38 in chloroform-methanol-water (65:35:5, v/v), chloroform-methanol-ammonium hydroxide (65:35:5, v/v), and chloroform-methanol-90% acetic acid (30:4:20, v/v)6), respectively. Chromatography of the phosphosulfolipid on silicic acid-impregnated paper in diisobutylketone-acetic acid-water (40:25 : 5, v/v/v) 7), showed a single acidic component with R~ 0.43, giving a blue fluorescence under UV light after staining with Rhodamine 6G 7), and a positive reaction (blue) with the phosphate-detecting spray of Dittmer and LesterS). It gave negative reactions with the periodate-Schiff reagent for vicinal diol groups v), with the ninhydrin reagent for free amino functions T), with the acetaldehydenitroprusside reagent a) or the Chlorox-benzidine spray for secondary amino or amido groups10), and with the ~-naphthol spray for sugarsXl).