Figure 6.

All-trans-retinal exit pathway near the extracellular side of green opsin. The retinylidene Schiff base and K312 are represented by spheres. H/D exchange of the dark state was subtracted from that of the bleached state, and the difference is displayed on TMs shown as a cartoon. H/D exchange itself is color-coded as follows: dark blue for 0–4%, light blue for 5–9%, cyan for 10–14%, cadet blue for 15–19%, green for 20–24%, light green for 25–29%, yellow for 30–34%, orange for 35–39%, and red for 40–44%. Undefined regions are colored gray. A possible exchange route for water or all-trans-retinal is indicated with a yellow arrow.