Fig. 4. bR-WT reaction cycle kinetics in the purple membrane.
After photon capture and isomerization of the retinal from all-trans to 13-cis, bR is in a closed state structure for 2.9 ms (pink), comprising states K, L and M. For re-protonation of the retinal, bR opens the cytoplasmic gate displacing the E-F loop and stays in the open state structure for 13.2 ms (green), corresponding to state N. The green arrow highlights the movement of the E-F loop to open the cytoplasmic gate. After retinal re-protonation and isomerization to all-trans, bR relaxes to the dark state structure (red). Under continuous light at saturating conditions, the protomer stays in the closed state for 37.6 ms (40.5 ms − 2.9 ms), until it can be activated again. We propose that, during this time, the neighboring protomers cycle (2 × 2.9 ms + 13.2 ms = 32.2 ms). The structure shown are PDB 6RNJ, 6RPH and 6RQP7.