Figure 6.

Summary of proton transfer processes in ReaChR. 1) During D → K transition, Glu¹³⁰ experiences a hydrogen bond change and then 2) deprotonates at the latest in the M state. 3) Asp²⁹³ receives a proton from the RSBH⁺ during M formation. 4) M decays via two pathways: (i) direct transition to D and (ii) transition to N. 5) Asp¹⁹⁶ undergoes a hydrogen bond change during M → N transition, and 6) Asp¹⁹⁶ deprotonates after M decay, presumably in the N → O transition. The proton transfer reactions are reversed in the O → D and M → D transitions, respectively. The structure was obtained by homology modeling with SWISS-MODEL using the crystal structure of C1C2 (Protein Data Bank code 3ug9) (25) as a template. Residues discussed in this work are highlighted.