Vertebrate vision critically depends on an 11-cis-retinoid renewal system known as the visual cycle. At the heart of this metabolic pathway is an enzyme known as retinal pigment epithelium 65 kDa protein (RPE65), which catalyzes an unusual, possibly biochemically unique, reaction consisting of a coupled all-trans-retinyl ester hydrolysis and alkene geometric isomerization to produce 11-cis-retinol. Early work on this isomerohydrolase demonstrated its membership to the carotenoid cleavage dioxygenase superfamily and its essentiality for 11-cis-retinal production in the vertebrate retina. Three independent studies published in 2005 established RPE65 as the actual isomerohydrolase instead of a retinoid-binding protein as previously believed. Since the last devoted review of RPE65 enzymology appeared in this journal, major advances have been made in a number of areas including our understanding of the mechanistic details of RPE65 isomerohydrolase activity, its phylogenetic origins, the relationship of its membrane binding affinity to its catalytic activity, its role in visual chromophore production for rods and cones, its modulation by macromolecules and small molecules, and the involvement of RPE65 mutations in the development of retinal diseases. In this article, I will review these areas of progress with the goal of integrating results from the varied experimental approaches to provide a comprehensive picture of RPE65 biochemistry. Key outstanding questions that may prove to be fruitful future research pursuits will also be highlighted.

脊椎动物的视觉严重依赖于称为视觉循环的11-顺式-类视黄醇更新系统。这种代谢途径的核心是一种称为视网膜色素上皮 65 kDa 蛋白 (RPE65) 的酶，它催化一种不寻常的、可能在生物化学上独一无二的反应，该反应由偶联的全反式视黄酯水解和烯烃几何异构化组成，产生11 -顺式视黄醇。对这种异构水解酶的早期研究证明了它属于类胡萝卜素裂解双加氧酶超家族及其对 11- cis的重要性-脊椎动物视网膜中的视网膜产生。2005 年发表的三项独立研究证实 RPE65 是真正的异构水解酶，而不是之前认为的类视黄醇结合蛋白。自从本期刊发表上一篇关于 RPE65 酶学的专门综述以来，我们在许多领域取得了重大进展，包括我们对 RPE65 异构水解酶活性的机制细节、其系统发育起源、其膜结合亲和力与其催化活性的关系的理解，它在视杆细胞和视锥细胞的视觉发色团产生中的作用，它通过大分子和小分子的调节，以及 RPE65 突变在视网膜疾病发展中的作用。在本文中，我将回顾这些进展领域，目标是整合来自不同实验方法的结果，以提供 RPE65 生物化学的全面图景。还将强调可能被证明是富有成果的未来研究追求的关键未决问题。