Rhodopsin photoresponse

Figure 2.9 (a) Light-responsive rod cell from the human retina. The photoresponsive pigment rhodopsin... 

Metarhodopsin II is inactivated by phosphorylation of three serine residues at the carboxyl terminal of the protein, catalyzed by rhodopsin kinase. In transgenic mice with carboxyl terminal-truncated rhodopsin, lacking the phosphorylation sites, there is a prolonged response to a single photon. Rhodopsin kinase is activated by its substrate, metarhodopsin II, and is inhibited by calcium bound to the protein recoverin, which thus prolongs the photoresponse. 

The above reasoning was recently confirmed by several pieces of indirect evidence. It was found that in H. halobium (i) protonophorous uncouplers decrease A/in and cause a repellent effect [45], (ii) cyanide and DCCD have no effect on the photoresponse of a mutant which possesses sensory rhodopsins but no bacteriorhodopsin [48], and (iii) in a similar mutant, A l is not involved in photosensing [49]. 

Figure 2.9 (a) Light-responsive rod cell from the human retina. The photoresponsive pigment rhodopsin is located in the outer lamellae. The foot makes contact with the optic nerve, (b) Operation of the rod cell. 

Cartoon representation of the three-dimensional structures of three different photoresponsive proteins. Left GFP with its HBDI anionic chromophore. Center the bovine visual pigment rhodopsin together with the cationic PSB11 chromophore. Right bacteriorhodopsin and its PSBAT chromophore... 

More recently, so-called photoresponsive crown ethers have also been prepared and, in these too, the light-sensitive behavior is based on Z,E-isomerization. The study of azo-groups in polymers has been undertaken recently. Switching processes have been an intensively studied domain in recent years as show in some recent papers. > Z,E-isomerization also plays an important role in simpler compounds such as benzylidene anilines and azomethines. The latter are of importance in biological systems such as rhodopsin in the human eye. ... 

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