Lipid-protein associations in chromatophores from the photosynthetic bacterium Rhodopseudomonas sphaeroides.
Lipid-protein interactions were examined in chromatophores isolated from the photosynthetic bacterium Rhodopseudomonas sphaeroides using lipid spin-labels. The chromatophores contain fluid bilayer and a significant amount of lipid immobilized by membrane proteins. For a typical preparation of cells grown under 600 ft-c illumination, 59% of the spin-labeled fatty acids were bound. Essentially the entire length of the 18-carbon fatty acid chain was immobilized, judging from results obtained with the spin-label at the 7, 12, and 16 positions. The amount immobilized varies directly with the bacteriochlorophyll content of the chromatophore material, suggesting that a significant fraction of the lipid spin-labels is immoblized on the hydrophobic surfaces of the chlorophyll-binding proteins. Changing the lipid spin-label head group from a negatively charged carboxyl group to a positively charged quarternary amine greatly decreased the amount of immobilized lipid. The changes in immobilized lipid with light level and polar head group suggest that the anntenna bacteriochlorophyll-binding proteins preferentially associate with negatively charged lipids.
D020130:Bacterial Chromatophores / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D001429:Bacteriochlorophylls / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D010743:Phospholipids / Q000378:metabolism*; D010788:Photosynthesis; D011485:Protein Binding; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D013113:Spin Labels
D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D010743:Phospholipids; D013113:Spin Labels