Fig. 11. Model of the GC regulation by GCAP1.
In the presence of μm [Ca2+]free GCAP1 inhibits GC activity (left). It is still unclear, whether an extra-cellular (intradiscal) ligand regulates GC activity. Upon illumination, GCAP1 causes change in the GC, increasing the enzymatic activity of cGMP production (right). In this model, binding of Ca2+ to GCAP1 does not cause dimerization, whereas GC is a dimer.