[Molecular mechanisms of photoreception. VI. Cyclic nucleotide- and light-dependent phosphorylation of rod outer segment proteins in the frog retina].

Phosphorylation of proteins in purified rod outer segment from frog retina was investigated. Phosphorylation of 18, 17, 12 and 11.5 kDa proteins was stimulated by cAMP (Ka approximately equal to 10(-7) M) and cGMP (Ka approximately equal to 10(-4) M). 32P-incorporation into 18 and 17 kDa proteins was much lower than into 12 and 11.5 kDa, which are in the group of main phosphoproteins of the rod outer segment: 12 and 11.5 kDA phosphoproteins appear to be present in cytoplasm or are slightly bound to disk's membranes. However, they are not discovered in the cytoplasmic membranes. The dephosphorylation of low-molecular weight proteins, discovered earlier by Polans et al., occurs slowly: the light doesn't change the level of phosphorylation of proteins in living retina within the time of photoresponse. It is suggested that the process of light-dependent phosphorylation-dephosphorylation of 12 and 11.5 kDa proteins controls the light sensitivity of the photoreceptor.