title: Cis-retinoids and the chemistry of vision.
abstract: We discuss here principal biochemical transformations of retinoid molecules in the visual cycle. We focus our analysis on the accumulating evidence of alternate pathways and functional redundancies in the cycle. The efficiency of the visual cycle depends, on one hand, on fast regeneration of the photo-bleached chromophores. On the other hand, it is crucial that the cyclic process should be highly selective to avoid accumulation of byproducts. The state-of-the-art knowledge indicates that single enzymatically active components of the cycle are not strictly selective and may require chaperones to enhance their rates. It appears that protein-protein interactions significantly improve the biological stability of the visual cycle. In particular, synthesis of thermodynamically less stable 11-cis-retinoid conformers is favored by physical interactions of the isomerases present in the retina with cellular retinaldehyde binding protein.
authors.affiliation: Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland. Electronic address: michele.cascella@iac.unibe.ch.
authors.forename: Michele
authors.initials: M
authors.lastname: Cascella
authors.forename: Simon
authors.initials: S
authors.lastname: Bärfuss
authors.forename: Achim
authors.initials: A
authors.lastname: Stocker
mesh_terms: D000818:Animals; D004224:Diterpenes / Q000737:chemistry / Q000378:metabolism; D005136:Eye Proteins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D006801:Humans; D010775:Photic Stimulation / Q000379:methods; D012160:Retina / Q000737:chemistry* / Q000201:enzymology / Q000378:metabolism; D017948:Retinal Rod Photoreceptor Cells / Q000201:enzymology / Q000378:metabolism / Q000502:physiology; D012176:Retinoids / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D014785:Vision, Ocular / Q000502:physiology*; D019745:cis-trans-Isomerases / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*
chemical_list: D004224:Diterpenes; D005136:Eye Proteins; D012176:Retinoids; C009167:retinylamine; D019745:cis-trans-Isomerases
keywords: 11-Cis-retinal; 9-Cis-retinal; Chaperone; Isomerase; Visual cycle; Vitamin A