title: Blue and ultraviolet light-absorbing opsin from the retinal pigment epithelium.
abstract: The retinal pigment epithelium (RPE) contains an abundant opsin that is distinct from rhodopsin and cone visual pigments and is able to bind the retinaldehyde chromophore. The putative retinal G protein-coupled receptor (RGR) was isolated in digitonin solution from bovine RPE microsomes and copurified consistently with a minor 34-kDa protein. The absorption spectrum of RGR revealed endogenous pH-sensitive absorbance in the blue and near-ultraviolet regions of light. Membrane-bound RGR was incubated with exogenously added all-trans-retinal and formed two long-lived pH-dependent photopigments with absorption maxima of 469 +/- 2.4 and 370 +/- 7.3 nm. The effects of hydrogen ion concentration suggest that the blue and near-UV photopigments are tautomeric forms of RGR, in which an all-trans-retinal Schiff base is protonated or unprotonated, respectively. The RPE pigment was also demonstrable by its reactivity to hydroxylamine in the dark. The retinaldehyde-RGR conjugate at neutral pH favors the near-UV pigment and is a novel light-absorbing opsin in the vertebrate eye.
authors.affiliation: Department of Microbiology, University of Southern California School of Medicine, Los Angeles, USA.
authors.forename: W
authors.initials: W
authors.lastname: Hao
authors.forename: H K
authors.initials: HK
authors.lastname: Fong
mesh_terms: D000818:Animals; D002417:Cattle; D005136:Eye Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000528:radiation effects; D019204:GTP-Binding Proteins / Q000302:isolation & purification; D006863:Hydrogen-Ion Concentration; D019811:Hydroxylamine; D006898:Hydroxylamines; D066298:In Vitro Techniques; D008027:Light; D010857:Pigment Epithelium of Eye / Q000737:chemistry* / Q000528:radiation effects*; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000302:isolation & purification / Q000528:radiation effects; D043562:Receptors, G-Protein-Coupled; D012172:Retinaldehyde / Q000737:chemistry / Q000528:radiation effects; D017299:Rod Opsins / Q000737:chemistry* / Q000302:isolation & purification / Q000528:radiation effects*; D012545:Schiff Bases / Q000302:isolation & purification; D013053:Spectrophotometry; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism; D014466:Ultraviolet Rays
chemical_list: D005136:Eye Proteins; C089754:G protein-coupled receptor RGR; D006898:Hydroxylamines; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D017299:Rod Opsins; D012545:Schiff Bases; D019811:Hydroxylamine; D019204:GTP-Binding Proteins; D012172:Retinaldehyde