Protein-Chromophore Interactions in Rhodopsin Studied by Site-directed Mutagenesis
This extract was created in the absence of an abstract.
Excerpt
Visual pigments are the light-absorbing proteins in the retina that initiate phototransduction. Each consists of an integral membrane protein, opsin, covalently joined via a protonated Schiff's base to a chromophore, 11-cis retinal (or in some instances, a closely related retinal). Visual pigments are members of a large family of cell-surface receptors, including many hormone receptors, that convey and amplify stimulus information by activating G proteins. Upon photoexcitation, the visual pigment chromophore, 11-cis retinal, is isomerized in situ from cis to trans (Fig. 1A). This isomerization and the accompanying activation of the visual pigment are analogous to the replacement of an tagonist by an agonist in the binding pocket of one of the related hormone receptors.
The absorbance spectra of a large number of visual pigments have been determined, and these spectra have in common a broad bell shape, closely resembling the shape of a protonated Schiff s base of retinal...
