THE EFFECT OF RECOMBINANT RECOVERIN ON THE PHOTORESPONSE OF TRUNCATEDROD PHOTORECEPTORS

Recoverin is a heterogeneously acylated calcium-binding protein though t to regulate visual transduction. Its effect on the photoresponse was investigated by dialyzing the recombinant protein into truncated sala mander rod outer segments. At high Ca2+ (Ca), myristoylated recoverin (Ca-recoverin) prolonged the recovery phase of the bright flash respon se but had less effect on the dim flash response. The prolongation of recovery had an apparent K-d for Ca of 13 mu M and a Hill coefficient of 2. The prolongation was shown to be mediated by inhibition of rhodo psin deactivation. After a sudden imposed drop in Ca concentration, th e effect of recoverin switched off with little lag. The myristoyl (C14 :0) modification of recoverin increased its activity 12-fold, and the C12:0 or C14:2 acyl group gave similar effects. These experiments supp ort the notion that recoverin mediates Ca-dependent inhibition of rhod opsin phosphorylation and thereby controls light-triggered phosphodies terase activity, particularly at high light levels.