Figure 12.3.

pH dependence of transducin activation by human red cone opsin in the absence and presence of 11-cis retinal and light. Human cone opsins were incubated with ethanol for opsin alone (open circles), and 11-cis retinal in the dark (filled triangles), 11-cis retinal followed by photobleaching (open triangles). Membranes from mock transfected COS-1 cells were used to measure activity of transducin in the absence of opsin and ligand (X). The following buffers were used to set the pH: MES for pH 5.1–6.4 and HEPES for pH 6.8–8.1.