Light-induced interactions between rhodopsin and the GTP-binding protein. Relation with phosphodiesterase activation

Eur J Biochem. 1982 Mar;123(1):133-9. doi: 10.1111/j.1432-1033.1982.tb06509.x.


The existence of rapid light-induced changes of light scattering in suspensions of bovine rod outer segment membranes has been described previously [H. Kühn et al. (1981) Proc. Natl Acad. Sci. USA, 78, 6873-6877]. The signal observed in the presence of GTP has been interpreted as being related to the rhodopsin-catalyzed exchange of GTP for GDP bound to the GTP-binding protein, i.e. to the formation of the activator of the cGMP phosphodiesterase [B.K.K. Fung et al. (1981) Proc. Natl Acad. Sci. USA, 78, 152-156]. We have tested this interpretation in the present paper by investigating the relation between the light-scattering signal and the activity of the phosphodiesterase using rapid recording techniques for both processes. All the results obtained are consistent with the above hypothesis. The amplitude of the light-scattering signal and the activity of the phosphodiesterase are shown to present the same dependence upon the flash intensity and upon the concentration of GTP or its analog guanosine 5'-[beta, gamma--imido]triphosphate (p[NH]ppG). The results suggest that the GTP-binding protein possesses one high-affinity p[NH]ppG-binding site (Kd much less than 0.1 microM). At high concentrations of GTP or p[NH]ppG the phosphodiesterase is activated in the dark and the light-scattering signal is correspondingly reduced; both effects are prevented by previous incubation with guanosine 5'-[beta-thio]diphosphate (p[S]pG).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3',5'-Cyclic-GMP Phosphodiesterases / metabolism*
  • Animals
  • Cattle
  • Enzyme Activation / drug effects
  • GTP-Binding Proteins
  • Guanosine Diphosphate / analogs & derivatives
  • Guanosine Diphosphate / pharmacology
  • Guanosine Triphosphate / pharmacology
  • Guanylyl Imidodiphosphate / pharmacology
  • Light*
  • Receptors, Cell Surface / metabolism*
  • Retinal Pigments / radiation effects*
  • Rhodopsin / radiation effects*
  • Scattering, Radiation
  • Thionucleotides / pharmacology


  • Receptors, Cell Surface
  • Retinal Pigments
  • Thionucleotides
  • Guanosine Diphosphate
  • 6-thioguanosine 5'-diphosphate
  • Guanylyl Imidodiphosphate
  • Guanosine Triphosphate
  • Rhodopsin
  • 3',5'-Cyclic-GMP Phosphodiesterases
  • GTP-Binding Proteins