page_title: RPE65
section_title: Function
hierarchical_section_title: RPE65 / Function
caption_attribution_description: English: The reaction completed by RPE65 in the retenoid cycle
context_page_description: Retinal pigment epithelium-specific 65 kDa protein, also known as retinoid isomerohydrolase, is an enzyme of the vertebrate visual cycle that is encoded in humans by the RPE65 gene. RPE65 is expressed in the retinal pigment epithelium and is responsible for the conversion of all-trans-retinyl esters to 11-cis-retinol during phototransduction. 11-cis-retinol is then used in visual pigment regeneration in photoreceptor cells. RPE65 belongs to the carotenoid oxygenase family of enzymes.
context_section_description: RPE65 is a critical enzyme in the vertebrate visual cycle found the retinal pigmented epithelium. It is also found in rods and cones. The photoisomerization of 11-cis-retinal to all-trans-retinal initiates the phototransduction pathway through which the brain detects light. All-trans-retinol is not photoactive and therefore must be reconverted to 11-cis-retinal before it can recombine with opsin to form an active visual pigment. RPE65 reverses the photoisomerization by converting an all-trans-retinyl ester to 11-cis-retinol.  Most commonly, the ester substrate is retinyl palmitate. The other enzymes of the visual cycle complete the reactions necessary to oxidize and esterify all-trans-retinol to a retinyl ester (RPE65's substrate) and to oxidize 11-cis-retinol to 11-cis-retinal (the required photoactive visual pigment component). 
  RPE65 is also referred to as retinol isomerase or retinoid isomerase, owing to past debates about the enzyme's substrate and whether it was involved in ester hydrolysis.
caption: The reaction completed by RPE65 in the retinoid cycle.
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