PURIFICATION AND PHYSIOLOGICAL EVALUATION OF A GUANYLATE-CYCLASE ACTIVATING PROTEIN FROM RETINAL RODS

In retinal rods light triggers a cascade of enzymatic reactions that i ncreases cGMP hydrolysis and generates an electrical signal by causing closure of cGMP-gated ion channels in the photoreceptor outer segment . This leads to a decrease in internal Ca, which activates guanylate c yclase and promotes photoresponse recovery by stimulating the resynthe sis of cGMP. We report here that the activation of guanylate cyclase b y low Ca is mediated by an approximate to 20-kDa protein purified from bovine rod outer segments by using DEAE-Sepharose, hydroxylapatite, a nd reverse-phase chromatographies. In a reconstituted system, this pro tein restores the Ca-sensitive regulation of guanylate cyclase and whe n dialyzed into functionally intact lizard rod outer segment decreases the sensitivity, time to peak, and recovery time of the flash respons e.