Calcium-sensitive control of rhodopsin phosphorylation in the reconstituted system consisting of photoreceptor membranes, rhodopsin kinase and recoverin.

Rhodopsin phosphorylation in the reconstituted system consisting of urea-washed photoreceptor membranes, rhodopsin kinase and recoverin is regulated by Ca2+: the process takes place at low [Ca2+] but is suppressed at high [Ca2+]. In the absence of recoverin, rhodopsin kinase is active irrespective of the cation concentration used. Hence, recoverin is an inhibitor (at high [Ca2+]) but not an activator of rhodopsin kinase. Based jointly on these data obtained on the reconstituted system and on our preceding experiments on rod outer segments suspension, one may conclude that (i) the function of recoverin in retina rod cells is the Ca(2+)-sensitive control of rhodopsin phosphorylation and (ii) the presence of recoverin is essential and sufficient to provide rhodopsin kinase with the Ca2+ sensitivity.