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An important class of calcium-binding proteins present in retinal photoreceptor cells includes recoverin from mammalian rods, guanylate cyclase-activating proteins (GCAP-1, GCAP-2, and GCAP-3) from mammalian rods and cones, and guanylate cyclase inhibitory protein (GCIP) from frog rods. The recoverin branch of the EF-hand superfamily includes neuronal Ca²⁺ sensors such as neurocalcin, frequenin, and hippocalcin. Mass spectrometric analysis of retinal recoverin and the GCAP proteins revealed that they are myristoylated at the amino terminus. GCAP-2 exhibits different membrane-targeting properties from those of recoverin. The myristoylated and unmyristoylated forms of GCAP-2 bind to membranes at low Ca²⁺ concentrations (<100 nM). The GCAP-2 membrane interaction is highly sensitive to ionic strength and is much stronger at higher salt concentrations (>50 mM NaCl).This …