Opsin,

Isralewitz et eil., 1997] Isralewitz, B., Izrailev, S., and Schulten, K. Binding pathway of retinal to bacterio-opsin A prediction by molecular dynamics simulations. Biophys. J. 73 (1997) 2972-2979... 

FIGURE 17 11 Imine formation between the aldehyde function of 11 as retinal and an ammo group of a protein (opsin) is involved in the chemistry of vision The numbering scheme in retinal is specifically developed for carotenes and related compounds... 

The distribution of rods and cones is shown in Figure 3b centered about the fovea, the area of the retina that has the highest concentration of cones with essentially no rods and also has the best resolving capabiUty, with a resolution about one minute of arc. The fovea is nominally taken as a 5° zone, with its central 1° zone designated the foveola. There are about 40 R and 20 G cones for each B cone in the eye as a whole, whereas in the fovea there are almost no B cones. A result of this is that color perception depends on the angle of the cone of light received by the eye. The extremely complex chemistry involved in the stimulation of opsin molecules, such as the rhodopsin of the rods, and the neural connections in the retinal pathway are well covered in Reference 21. 

FIGURE 18.36 The incorporation of retinal into the light-sensitive protein rhodopsin involves several steps. All- ram-retinol is oxidized by retinol dehydrogenase and then iso-merized to ll-cis-retinal, which forms a Schiff base linkage with opsin to form light-sensitive rhodopsin. 

Opsins Odorant Monoamine Lipid messengers Nucleotide... 

Bleaching is reversed in the dark and the red-purple color of rhodopsin returns. This is thought to occur by the reduction of all-Pms-retinal to vitamin Ai (retinal), which diffuses from the rod into the pigment epithelium, where it is converted enzymatically to the 1 l-c isomer of vitamin At. The enzymatic isomerization is followed by diffusion back into the rod, oxidation to 11 -rfr-retinal, and combination with opsin to form rhodopsin. This process is shown schematically in Figure 12.5.[Pg.289]

The visual pigment present in rods has been termed rhodopsin and consists of 11-m-retinal, a derivative of vitamin A1( and a lipoprotein called opsin. Recent evidence(43) suggests that in native rhodopsin the retinal chromo-phore is covalently bonded to a phosphatidylethanolamine residue of the lipid portion of opsin. The structure of 1 l-cis-retinal is as follows ... 

The bleaching of rhodopsin has been found to lead to the all-trans form of retinal through several intermediate steps.(llb,45) These steps are temperature dependent consequently low temperatures must be used to observe the intermediate products. A solution of rhodopsin is subjected to a flash of light at liquid nitrogen temperature and intermediates are detected by changes in the absorption spectrum. The first intermediate, with an absorption maximum at 543 nm, believed to be an all-fra/w-retinal bound to opsin, has been termed prelumirhodopsin. Warming the sample to a temperature greater than... 

Schadel, SA, Heck, M, Maretzki, D, Filipek, S, Teller, DC, Palczewski, K, and Hofmann, KP, 2003. Ligand channeling within a G-protein-coupled receptor—The entry and exit of retinals in native opsin. J Biol Chem 278, 24896-24903. 

Prado, M. M., A. Prado-Cabrero et al. (2004). A gene of the opsin family in the carotenoid gene cluster of Fusarium fujikuroi. Curr. Genet. 46(1) 47-58. 

Rhodopsin is a seven ot-helix trans-membrane protein and visual pigment of the vertebrate rod photoreceptor cells that mediate dim light vision. In this photoreceptor, retinal is the chromophore bound by opsin protein, covalently linked to Lys296 by a Schiff base linkage. Kpega et al.64 have studied NMR spectra of Schiff bases being derivatives of all-frans retinal and amino-p-cyclodextrins as a model of rhodopsin, where p-cyclodextrin plays a role of a binding pocket. On the basis of analysis of the chemical shift differences for the model compound in the presence and in the absence of adamantane carboxylate, it has been shown that the derivative of 3-amino-p-cyclodextrin forms dimer in water and retinoid is inserted into p-cyclodextrin cavity [31]. 

Rhodopsin is a transmembrane protein linked to 1 l as-retinal, which, on photoabsorption, decomposes to opsin and all-trans-retinal 809... 

Cone-cell pigments contain different opsins that have high-sequence homology 812... 

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... 

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