@entity6708 influences XXXX binding to frog photoreceptor G-protein.

@entity6708 @entity3007 @entity6370 @entity8695 @entity3006
A rapid light-induced decrease in @entity6708 is thought to play a role in regulating the permeability or light sensitivity of photoreceptor membranes. Photo-excited @entity8695 activates a @entity6370 -binding protein (G-protein) by catalyzing the exchange of bound @entity3006 for @entity3007 . This G-protein X @entity3007 complex activates the phosphodiesterase resulting in a decrease in @entity6708 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 @entity3006 binds to G-protein with an affinity similar to that of @entity3007 . These two nucleotides appear to compete for a common site. Since G-protein X @entity3006 does not activate phosphodiesterase, light-induced changes in the @entity3007 / @entity3006 ratio known to occur on illumination may serve to reduce G-protein activation and hence reduce phosphodiesterase activation. Second, addition of @entity6708 in the presence of equimolar @entity3007 and @entity3006 causes @entity3007 binding to G-protein to be enhanced compared to @entity3006 binding. This effect increases as the @entity6708 concentration is increased from 0.05 to 2 mM. Thus, light-induced decreases in @entity6708 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.
