cGMP influences guanine nucleotide binding to frog photoreceptor G-protein.

Academic Article


  • A rapid light-induced decrease in cGMP is thought to play a role in regulating the permeability or light sensitivity of photoreceptor membranes. Photo-excited rhodopsin activates a guanine nucleotide-binding protein (G-protein) by catalyzing the exchange of bound GDP for GTP. This G-protein X GTP complex activates the phosphodiesterase resulting in a decrease in cGMP concentration. We have observed two processes in vitro which may be relevant for the regulation of G-protein activation. First, we have found that free GDP binds to G-protein with an affinity similar to that of GTP. These two nucleotides appear to compete for a common site. Since G-protein X GDP does not activate phosphodiesterase, light-induced changes in the GTP/GDP ratio known to occur on illumination may serve to reduce G-protein activation and hence reduce phosphodiesterase activation. Second, addition of cGMP in the presence of equimolar GTP and GDP causes GTP binding to G-protein to be enhanced compared to GDP binding. This effect increases as the cGMP concentration is increased from 0.05 to 2 mM. Thus, light-induced decreases in cGMP concentration may also act as a feedback control in reducing G-protein activation. One or both of these processes may be involved in the desensitization (light adaptation) of rod photoreceptors.
  • Authors

  • Robinson, PR
  • Radeke, MJ
  • Cote, Rick
  • Bownds, MD
  • Status

    Publication Date

  • January 5, 1986
  • Published In


  • Animals
  • Binding Sites
  • Cyclic GMP
  • GTP-Binding Proteins
  • Guanine Nucleotides
  • Guanosine Diphosphate
  • Guanosine Triphosphate
  • Light
  • Photoreceptor Cells
  • Rana catesbeiana
  • Ranidae
  • Rod Cell Outer Segment
  • Digital Object Identifier (doi)

    Pubmed Id

  • 3001052
  • Start Page

  • 313
  • End Page

  • 318
  • Volume

  • 261
  • Issue

  • 1