Figure 5.

Regulation of guanylyl cyclase by small molecular-weight Ca²⁺-binding guanylyl cyclase activating proteins (GCAPs). A: Schematic drawing indicating binding of Ca²⁺ and small molecular-weight GCAPs to cyclase. B: Comparison of mean responses from 41 wild-type (WT) rods (black) and 21 rods lacking the genes for the GCAP proteins (green). Single-photon responses were calculated from the squared mean and variance (for example [66]). Currents have been normalized to the circulating current in darkness, giving the faction of channels closed as a function of time. The fraction of channels closed is thus the same as the normalized current defined in the legends to Figs. 2–4.