Light-induced FTIR difference spectroscopy of the S2-to-S3 state transition of the oxygen-evolving complex in Photosystem II

AbstractWe have applied flash-induced FTIR spectroscopy to study structural changes upon the S2-to-S3 state transition of the oxygen-evolving complex (OEC) in Photosystem II (PSII). We found that several modes in the difference IR spectrum are associated with bond rearrangements induced by the second laser flash. Most of these IR modes are absent in spectra of S2/S1, of the acceptor-side non-heme ion, of Y⋅D/YD and of S3′/S2′ from Ca-depleted PSII preparations. Our results suggest that these IR modes most likely originate from structural changes in the oxygen-evolving complex itself upon the S2-to-S3 state transition in PSII