Figure 4. Visual pigments Rh1 and Rh6 in the photosteady state in a rhabdomeric microvillus with total R ₀ = 1000 visual pigment molecules, assuming different amounts of arrestin and enzymatic rate constants, as a function of light intensity (logI; see text).

A‐‐C, population in the photosteady state of the different visual pigment states, R_a, R_i, M_a and M_i, representative for Drosophila R1–6 photoreceptors, where the number of arrestin molecules in a microvillus is A ₀ = 370 of which arrestin is unbound, and turnover can be considered negligible. Illumination with broad‐band white light creates a photosteady state with 800 rhodopsin and 200 metarhodopsin molecules. D–F, population of the visual pigment states representative for a green receptor with 1000 arrestin molecules per microvillus, and assuming time constants of degradation and regeneration k _f ^–1 = 3 min and k _g ^–1 = 10 min.