Stochastic simulation of activation in the G-protein cascade of phototransduction

Biophys J. 1994 Oct;67(4):1439-54. doi: 10.1016/S0006-3495(94)80617-4.


Activation of the G-protein cascade underlying phototransduction has been modeled by simulating the two-dimensional diffusional interactions that occur at the rod disc membrane between the three reacting protein species, which are the activated rhodopsin (R*), the G-protein (G), and the effector protein (E, the phosphodiesterase, PDE). The stochastic simulations confirm the main predictions of a simplified analytical model (Lamb, T. D., and E. N. Pugh, 1992, Journal of Physiology 449:719-758), and extend that treatment to more complicated cases, where there is a finite probability of reaction or a finite time for reaction. The simulations also provide quantitative estimates of the efficiency of coupling from activated G-protein (G*) to activated effector (E*) in terms of the concentrations, lateral diffusion coefficients, and binding rate constants of the participating molecules; the efficiency of coupling from G* to E* is found to be not as high as in the previous simplified analytical theory. The findings can be extended to other G-protein cascades, provided that the physical parameters of those cascades are specified.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Diffusion
  • GTP-Binding Proteins / chemistry
  • GTP-Binding Proteins / physiology*
  • Guanosine Triphosphate / metabolism
  • Kinetics
  • Mathematics
  • Models, Biological*
  • Models, Structural
  • Photoreceptor Cells / physiology*
  • Signal Transduction*
  • Software
  • Stochastic Processes*
  • Time Factors


  • Guanosine Triphosphate
  • GTP-Binding Proteins