RHODOPSIN KINASE INHIBITION BY RECOVERIN - FUNCTION OF RECOVERIN MYRISTOYLATION

Recoverin is a Ca2+-binding protein that may play a role in vertebrate photoreceptor light adaptation by imparting Ca2+ sensitivity to rhodo psin kinase. It is heterogeneously acylated (mostly myristoylated) at its aminoterminal glycine. Recent studies have shown that recoverin my ristoylation is necessary for its Ca2+-dependent membrane association and cooperative Ca2+ binding. We have addressed several issues concern ing the role of recoverin myristoylation with respect to inhibition of rhodopsin kinase. We find that 1) myristoylation of recoverin is not necessary for inhibition of rhodopsin kinase, 2) myristoylation of rec overin induces a cooperative Ca2+-dependence for rhodopsin kinase inhi bition, and 3) each Ca2+-binding site on the nonmyristoylated recoveri n partially inhibits rhodopsin kinase. The available data suggest that the functions of recoverin myristoylation in the living rod are to in duce a sharp Ca2+ dependence of rhodopsin kinase inhibition and to bri ng this dependence into the rod's physiological Ca2+ concentration ran ge.