New insights into retinoid metabolism and cycling within the retina.
The retinoid cycle is a series of biochemical reactions within the eye that is responsible for synthesizing the chromophore, 11-cis retinal, for visual function. The chromophore is bound to G-protein coupled receptors, opsins, within rod and cone photoreceptor cells forming the photosensitive visual pigments. Integral to the sustained function of photoreceptors is the continuous generation of chromophore by the retinoid cycle through two separate processes, one that supplies both rods and cones and another that exclusively supplies cones. Recent findings such as RPE65 localization within cones and the pattern of distribution of retinoid metabolites within mouse and human retinas have challenged previous proposed schemes. This review will focus on recent findings regarding the transport of retinoids, the mechanisms by which chromophore is supplied to both rods and cones, and the metabolism of retinoids within the posterior segment of the eye.
Department of Neurosciences, Medical University of South Carolina, Charleston, SC 29425, USA.
Peter H
PH
Tang
Masahiro
M
Kono
Yiannis
Y
Koutalos
Zsolt
Z
Ablonczy
Rosalie K
RK
Crouch
D000818:Animals; D005136:Eye Proteins / Q000378:metabolism*; D006801:Humans; D012160:Retina / Q000378:metabolism*; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism*; D012168:Retinal Pigments / Q000378:metabolism*; D012176:Retinoids / Q000378:metabolism*
D005136:Eye Proteins; D012168:Retinal Pigments; D012176:Retinoids