C. Protein components of signaling mechanism in rod cells 1. A. Rhodopsin 1. Light-activated transducin cycle.
Photoexcited rhodopsin is switched off by phosphorylation and capping by arrestin.
B. PDE is deactivated by GTPase activity of Ta subunit. Rods are more sensitive than cones and are better for low light vision. For color vision, 11-cis retinal associates with 3 different proteins, forming complexes which absorb in the red, blue and green spectral regions. Thereafter, mechanistically the cone cells work like the rod cells, albeit requiring higher light levels.