Figure 2.

Functional activity of rhodopsin dimer by Meta-II transition and retinoid analyses. Shown are UV-visible spectra of DSP-cross-linked rhodopsin monomer (a and b) and dimer (d and e) fractionated by gel filtration and diluted with 1.0% OG (a and d) or 0.005% DDM (b and e). Dark- and light-activated rhodopsin spectra are indicated as solid lines and dashed lines, respectively. Difference spectra (after activation − before activation) for monomer (c) and dimer (f) are shown to expand the light-dependent formation of active Meta-II (380 nm) from dark rhodopsin (500 nm). g–j, retinoid analysis shows normal 11-cis-retinal to all-trans-retinal transition upon light activation; some 13-cis-retinal is observed as a by-product in all cases. The retinals in monomer in DDM (g) or in nanodiscs (h) and dimer in nanodiscs without cross-link (i) or with cross-link (j) were converted to corresponding retinal oximes and analyzed by HPLC monitoring the UV absorbance at 325 nm. Compared with the dark state (black line), light activation (red line) shows a shift from 11-cis-retinal to all-trans-retinal.