Characterization and Composition of the Purple and Red Membrane from Halobacterium cutirubrum

Abstract

The purple membrane (bacteriorhodopsin) isolated from cells of Halobacterium cutirubrum grown anaerobically in the light was shown to contain 77% protein and 20% lipids by weight. The protein component consisted of a single protein moeity, having a molecular weight of (19.6 ± 0.8) × 103, complexed with retinal in mole ratio of 2:1, respectively. The protein moeity is not glycosylated but may be phosphorylated (ca. 2 mol of phosphate per mole of protein). The red membrane contains 56% protein and 38% lipids, including bacterioruberins. Several polypeptide components are present including some which may be glycosylated and/or phosphorylated. The lipids of both membranes contained phosphatidyl glycerophosphate (52%) and phosphatidyl glycerol (3–4%) but the sulfated lipid components, glycolipid sulfate and phosphatidyl glycerosulfate, were present exclusively in the purple membrane, the red membrane containing instead two unidentified glycolipids. Neutral lipids (squalenes, vitamin MK-8, etc.) were present in both membranes to the extent of 7–9%.