Rhodopsin molecular weight

Rhodopsin is a transmembrane protein linked to 11-c/s-retinal, which, on photoabsorption, decomposes to opsin and all-f/a/75-retinal. Rhodopsin has a molecular weight of about 40,000. Its C-terminus is exposed on the cytoplasmic surface of the disk, and its sugar-containing... 

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. 

Wolken has worked with similar materials and converged on a molecular weight between those proposed by Krause and by Wald. He has proposed a molecular weight of 275,000 to 295,000 for the putative rhodopsin. 

The opsin consists of protein (ca. 80-85% of which is rhodopsin), phospholipids and carbohydrates and contains very little cholesterol (1-3%) (for a review, see [6]). While the molecular weight (e.g., 40000 for bovine rhodopsin) [7], carbohydrate [8,9], lipid and amino acid [10-12] composition have been established for some rhodopsins, there is as yet no example of a visual pigment for which the full amino acid sequence is known. Only a quarter of about the 300 residues of rhodopsin have been sequenced [13,14], 39 residues at the N-terminus and 40 residues at the C-terminus. The structure of the moiety containing retinal, i.e., retinal-lysine-alanine, which is located in the carboxy-terminal region has, however, been elucidated ([15] see also [78] and references therein). The N-terminal residue was identified as acetylmethionine [16]. 

The purple membrane is a unique patch of membrane in halobacteria [118-120] it contains a single protein of 26000 molecular weight and the protein is 75% of the mass of the membrane. The remainder is primarily phospholipid. The protein is called bacteriorhodopsin, in analogy to rhodopsin. Characterization by electron microscopy has shown the protein to be comprised of seven helical rods traversing back and forth across the membrane [121]. This is interpreted to indicate some 70-75% a-helix, the presence of which is also indicated from X-ray diffraction data [122,123]. Accordingly, the purple membrane provides an especially interesting opportunity to apply the preceding analyses for the correction of distortions in the ellipticity patterns of biomembranes. 

A small molecular weight oligosaccharide (16) attached separately at two sites near the A-terminus of bovine rhodopsin has been examined by a combination of methylation analysis, acetolysis, and enzymic studies. This structure is identical to a proposed intermediate in the biosynthesis of complex L-asparagine-linked oligosaccharides. Three oligosaccharides have been released from bovine rhodopsin by hydrazinolysis. One of the components has an identical structure to (16) except for the absence of the L-asparagine residue, and structures [(17) and (18)] were established for the other two oligosaccharides. 

The molecular weight of rhodopsin is 40 KD. A spherical molecule of this size would roughly have a diameter of about 45A. To check whether rhodopsin is spherical, energy-transfer experiments were performed. The protein already has a good donor in cis-retinal. Another fluor was tied to a sulfhydryl group in opsin. This fluor acted as the acceptor. 

The chemistry of ROS has been studied by several laboratories, and recently reviewed by Daemen (1973). Over 90% of the protein is rhodopsin, a photosensitive glycoprotein of molecular weight around 35,000, which is imbedded in a lipid bilayer. Phospholipids make up about 96% of the lipids of cattle ROS and cholesterol is the major component of the neutral lipid fraction. Phosphatidyl choline (PC) and phosphatidyl ethanolamine (PE) are the major phospholipids in all species examined, with phosphatidyl serine (PS), phosphatidyl inositol (PI), and sphingomyelin (SPh) present in lesser amounts (Anderson and Maude, 1972). Detailed analysis of the photoreceptor membranes of vertebrate species ranging from frogs to humans have revealed a fairly constant phospholipid class and protein composition (Basinger and Anderson, unpublished). 

The photosensitive pigment found in rods is called rhodopsin or visual purple. Its retinal is 11-cis-retinal and its opsin is scotopsin. Rhodopsin shows absorption maximum at - 500 nm. Human rhodopsin has molecular weight 41000 and 348 amino acid residues. The 90% of the total protein in the membrane of red disk are made up of rhodopsin. It is coupled with G-protein as ... 

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