Rhodopsin lipid-sensitized

A different vesicular photoimaging material consists of an assembly of lipid vesicles sensitized with rhodopsin. In one system the vesicles can be filled with a solution containing Co2+, and the solution outside the vesicles can be free of metal ions but contain a chelating indicator dye such as xylenol orange (101). The whole assembly can be coated, and when exposed to actinic radiation the vesicles are disrupted in exposed areas and release Co2+ ions, which are complexed by the dye indicator, thereby forming an image.253... 

Krause in the 1930 s proposed that the chromophore of rhodopsin was similar chemically to the polymethine compounds known as cyanine dyes which are also used to sensitize photographic emulsions to the longer wavelengths of the visible spectrum. He proposed that the chromophore was bound to a very large lipid/protein complex with a molecular weight near 800,000. 

The lipid membrane provides shelter for membrane proteins to do their functions. However, instead of working alone, membrane proteins such as ion channels work together with the membrane, such that the lipid composition around the protein actually affects the activation and the functioning of the protein. This idea is largely the essence of the lipid raft model (8), which highlights the importance of lipids in a variety of cellular functions. It has been observed, for example, that rhodopsin, which is the light sensitive membrane protein, favors interactions with polyunsaturated lipids (9). 

Champeil, MoUer, 2000). Some lipid/detergent mixtures have been used in nuclear magnetic resonance (NMR) and crystallization experiments (Seddon, Cumow, Booth, 2004) in structural and functional studies of the extremely light-sensitive G protein-coupled receptor (GPCR), rhodopsin, Reeves et al. used a mixture of the lipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine and the detergent 3-[(3-cholamidopropyl)-dimethylammonio]- -propane-sulfonate (CHAPS) (Reeves, Hwa, Khorana, 1999). 

The thermal stability of rhodopsin, defined as the temperature at which in 10 min 50% of the 500 nm absorbance is lost, is indeed sensitive to changes in lipid environment (Table II, 2nd column). Whereas native rhodopsin has a high thermal stability (70°C), affinity chromatography and phospholipase-C treatment lower this parameter to 53 C and 59 C, respectively. Reconstitution of such delipidated preparations with egg phosphatidylcholine (66 mol per mol rhodopsin) to rhodopsin-lipid vesicles leads to full recovery of the thermal stability. 

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