When rhodopsin absorb light retinol is changed to its all-trans isomer
Rhodopsin breaks down into all-trans retinal + opsin (this process is called bleaching of the pigment )
Vitamin A oxidized to the 11-cis retinal form and combined with opsin to form rhodopsin.
CH 3 C C H H H 2 C H 2 C C C CH 3 H CH 3 C H C CH 3 C H C H C H C CH 3 C O H C H C C H H H 2 C H 2 C H 3 C C C C CH 3 CH 3 H C H C C O C H C H C C C H C CH 3 H CH 3 H Oxidation Rhodopsin Opsin All -trans retinal – 2H +2H Reduction Vitamin A Regeneration of the pigment: Slow conversion of all- trans retinal to its 11- cis form occurs in the pig- mented epithelium; requires isomerase enzyme and ATP. Dark Light 11- cis retinal All- trans isomer 11- cis isomer Bleaching of the pigment: Light absorption by rhodopsin triggers a series of steps in rapid succession in which retinal changes shape (11- cis to all- trans) and releases opsin. Figure 15.16