Photosynthetic water oxidation is performed through a light-driven cycle of five intermediates (S0-S4states) in photosystem II (PSII). The S2→ S3transition, which involves concerted water and proton transfer, is a key process for understanding the water oxidation mechanism. Here, to identify the water and proton transfer pathways during the S2→ S3transition, we examined the effects of D1-N298A mutation and NO3-substitution for Cl-, which perturbed the O1 and Cl channels, respectively, on the S2→ S3kinetics using time-resolved infrared spectroscopy. The S2→ S3transition was retarded both upon NO3-substitution and upon D1-N298A mutation, whereas it was unaffected by further NO3-substitution in N298A PSII. The H/D kinetic isotope effect in N298A PSII was relatively small, revealing that water transfer is a rate-limiting step in this mutant. From these results, it was suggested that during the S2→ S3transition, water delivery and proton release occur through the O1 and Cl channels, respectively.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry