... photoreceptorguanylyl cyclase by preventing a Ca21-induced ‘activator -to- inhibitor’ transition. J. Biol. Chem. 271, 19346– 19350.55. Craescu, C.T., Precheur, B., van Riel, A., Sakamoto, ... bothEF-hands of CR I–II are predicted to bind calcium. On theother hand, the residues at positions 66, 68 and 74 (G66, R68 and G74) of Calb I–II lack the side-chain oxygens expected to provide ... resolutionstructures of both apo- and calcium-bound domains areessential to understand fully the differences in CR I–II and Calb I–II structure and properties.Are the functions of CR and Calb distinct?A...