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Characterization and composition of the purple and red membrane from Halobacterium cutirubrum;
Abstract:
The purple membrance (bacteriorhodopsin) isolated from cells of Halobacterium cutirubrum grown anaerobically in the light was shown to contain 77% protein and 20% lipils by weight. The protein component consisted of a single protein moeity, having a molecular weight of (19.6 plus or minus 0.8) times 10-3, 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 membrance 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 75-8, etc.) were present in both membranes to the extent of 7-9%.
Insights
Bacteriorhodopsin, a purple membrane protein from Halobacterium cutirubrum, comprises protein and lipids. The red membrane differs in lipid composition, containing unique glycolipids and bacterioruberins.
Area of Science:
- Microbiology
- Biochemistry
- Membrane Biology
Background:
- Halobacterium cutirubrum possesses distinct purple and red membranes.
- These membranes have differing protein and lipid compositions.
- Bacteriorhodopsin is the primary protein in the purple membrane.
Purpose of the Study:
- To biochemically characterize the protein and lipid components of the purple and red membranes.
- To identify differences in lipid profiles between the two membrane types.
- To analyze the post-translational modifications of the purple membrane protein.
Main Methods:
- Isolation of purple and red membranes from Halobacterium cutirubrum.
- Gravimetric analysis to determine protein and lipid percentages.
- Molecular weight determination of the purple membrane protein.
- Lipid analysis using chromatography and mass spectrometry.
- Analysis of protein phosphorylation and glycosylation.
Main Results:
- Purple membrane: 77% protein (bacteriorhodopsin, MW 19.6 kDa), 20% lipids. Protein may be phosphorylated.
- Red membrane: 56% protein, 38% lipids (including bacterioruberins). Contains multiple polypeptides, some glycosylated/phosphorylated.
- Lipids: Both membranes contain phosphatidyl glycerophosphate and phosphatidyl glycerol.
- Purple membrane uniquely contains glycolipid sulfate and phosphatidyl glycerosulfate.
- Red membrane contains two unidentified glycolipids.
- Neutral lipids (squalenes) present in both membranes (7-9%).
Conclusions:
- Purple and red membranes of Halobacterium cutirubrum exhibit significant differences in lipid composition.
- The purple membrane's lipid profile is specialized, including unique sulfated lipids.
- Bacteriorhodopsin is a major, non-glycosylated protein component of the purple membrane, potentially phosphorylated.