Blue and ultraviolet light-absorbing opsin from the retinal pigment epithelium

Biochemistry. 1996 May 21;35(20):6251-6. doi: 10.1021/bi952420k.

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Cattle
  • Eye Proteins / chemistry*
  • Eye Proteins / isolation & purification
  • Eye Proteins / radiation effects
  • GTP-Binding Proteins / isolation & purification
  • Hydrogen-Ion Concentration
  • Hydroxylamine
  • Hydroxylamines
  • In Vitro Techniques
  • Light
  • Pigment Epithelium of Eye / chemistry*
  • Pigment Epithelium of Eye / radiation effects*
  • Receptors, Cell Surface / chemistry*
  • Receptors, Cell Surface / isolation & purification
  • Receptors, Cell Surface / radiation effects
  • Receptors, G-Protein-Coupled*
  • Retinaldehyde / chemistry
  • Retinaldehyde / radiation effects
  • Rod Opsins / chemistry*
  • Rod Opsins / isolation & purification
  • Rod Opsins / radiation effects*
  • Schiff Bases / isolation & purification
  • Spectrophotometry
  • Spectrophotometry, Ultraviolet
  • Stereoisomerism
  • Ultraviolet Rays

Substances

  • Eye Proteins
  • G protein-coupled receptor RGR
  • Hydroxylamines
  • Receptors, Cell Surface
  • Receptors, G-Protein-Coupled
  • Rod Opsins
  • Schiff Bases
  • Hydroxylamine
  • GTP-Binding Proteins
  • Retinaldehyde