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. Author manuscript; available in PMC: 2009 Sep 22.
Published in final edited form as: Cell. 2005 Aug 12;122(3):449–459. doi: 10.1016/j.cell.2005.06.042

Figure 1.

Figure 1

Visual Cycle for Regeneration of Rhodopsin

The light-sensitive protein in rods is rhodopsin, in the membranes of the outer segment. The 11-cis-retinaldehyde (11cRAL) chromophore is coupled to rhodopsin through a protonated Schiff-base linkage. Absorption of a photon (hv) induces 11-cis to all-trans isomerization of retinaldehyde to yield metarhodopsin, which activates the visual transduction cascade. The all-trans-retinaldehyde (atRAL) subsequently dissociates from apo-opsin and is reduced to all-trans-retinol (atROL) by all-trans-retinol dehydrogenase (atRDH). The atROL diffuses from the outer segment and is taken up by an RPE cell, where it is transferred to a fatty acid from phosphatidylcholine by lecithin-retinol acyl transferase (LRAT) to yield an all-trans-retinyl ester (atRE). The atRE is converted to 11-cis-retinol (11cROL) by the isomerase (shown here to be Rpe65). The 11cROL is oxidized by one of several 11cROL dehydrogenases (11cRDHs) to yield 11cRAL. 11cROL and 11cRAL are bound to CRALBP. The 11cRAL diffuses back to the outer segment where it combines with apo-opsin to form a new rhodopsin pigment molecule.