Photobleaching and cyclic GMP dependences of rhodopsin phosphorylation in rod outer segment.

The experimental data on the cGMP decrease under continuous illumination of rod outer segment have been theoretically analysed to study the bleaching and hence the cGMP dependence of the rhodopsin phosphorylation. From the agreement of the theoretical results with the experimental observations it has been found that the rate of phosphorylation depends on the rate of cGMP hydrolysis. If the rate of cGMP hydrolysis increases the rate of phosphorylation also increases. The results of the theoretical treatment predict that (i) the presence of cGMP in rod outer segment inhibits the rhodopsin phosphorylation and (ii) rhodopsin phosphorylation process is much faster than what has been reported in the literature.