2. <biochemistry> The aldehyde of retinol, derived by the oxidative enzymatic splitting of absorbed dietary carotene and having vitamin A activity. In the retina, retinal combines with opsins to form visual pigments. One isomer, 11 cis retinal combines with opsin in the rods (scotopsin) to form rhodopsin or visual purple. Another, all trans retinal (trans r.), visual yellow, xanthopsin) results from the bleaching of rhodopsin by light, in which the 11 cis form is converted to the all trans form. Retinal also combines with opsins in the cones (photopsins) to form the three pigments responsible for colour vision.
This entry appears with permission from the Dictionary of Cell and Molecular Biology
(11 Mar 2008)
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