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NL Mata, JS Lee, RS Clemmons, RA Radu, GH Travis; 11-cis Retinol Dehydrogenase Activity in the Cone-Dominant Retina . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3609.
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Purpose: Electrophysiological investigations of visual pigment regeneration have previously documented the unique ability of bleached cone photoreceptors to regain light sensitivity upon addition of 11-cis retinol (11c ROL). These findings provide indirect evidence for the existence of an 11-cis retinol dehydrogenase (11c RDH) activity within cone photoreceptors. To explore this possibility, we have characterized the dinucleotide and retinoid substrate specificities for dehydrogenase activities in rod- and cone-dominant retinal tissues. Methods: Membranes were prepared from retina and retinal pigment epithelium (RPE) of rod-dominant cattle and cone-dominant chicken and ground squirrel. These preparations were used in enzymatic assays with chemically defined dinucleotide and retinoid stereoisomers to study the substrate specificities and catalytic activities. Results: RPE membranes from each species examined demonstrated similar dinucleotide (pro-S-NAD) and retinoid (pro-S-11c ROL) specificities for production of 11-cis retinal (11c RAL). Rates of 11c RAL production from the three RPE preparations were also similar (0.4 - 0.6 nmole/min/mg). No redox activity for all-trans retinol or all-trans retinaldehyde (at RAL) was detectable. In retinal membranes from the three species, reduction of at RAL had pro-S dinucleotide and pro-S retinoid specificity as previously reported. The catalytic rates were also similar (5 - 10 nmole/min/mg). No redox activity for 11c ROL or 11c RAL was detectable in bovine retinal membranes. However, chicken and ground squirrel retinal membranes contained a pronounced pro-S-NADP/pro-R-11c ROL-specific dehydrogenase activity. Conclusion: The presence of 11c RDH activity in two cone-dominant retinas corroborates earlier electrophysiologic data indicating that cone photoreceptors utilize 11c ROL to regenerate visual chromophore. Moreover, the unique dinucleotide and retinoid substrate specificities of this "cone-specific" 11c RDH distinguish it from 11c RDH in the RPE and provide further support for an alternate biochemical route of visual-chromophore biosynthesis in cones.
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