Manganese K-edge X-ray absorption spectra of the cyclic S-states in the photosynthetic oxygen-evolving system

Abstract

A set of Mn K-edge XANES spectra due to the redox states S0-S3 of the OEC were determined by constructing a highly-sensitive X-ray detection system for use with physiologically native PS II membranes capable of cycling under a series of saturating laser-flashes. The spectra showed almost parallel upshifts with relatively high K-edge half-height energies given by 6550.9±0.2 eV, 6551.7±0.2 eV, 6552.5±0.2 eV and 6553.6±0.2 eV for the S0, S1, S2 and S3 states, respectively. The successive difference spectra between S0 and S1, S1 and S2, and S2 and S3 states were found to exhibit a similar peak around 6552-6553 eV, indicating that one Mn(III) ion or its direct ligand is univalently oxidized upon each individual S-state transition from S0 to S3. The present data, together with other observations of EPR and pre-edge XANES spectroscopy, suggest that the oxidation state of the Mn cluster undergoes a periodic change; S0: Mn(III,III,III,IV) → S1: Mn(III,IV,III,IV) → S2: Mn(III,IV,IV,IV) → S3: Mn(IV,IV,IV,IV) or Mn(III,IV,IV,IV)·L(+) with L being a direct ligand of a Mn(III) ion.

Primary reactions of oxygenic photosynthesis

“…9) in comparison with those of Mn model compounds. The results in [61] and [62] are shown in Table 1 C and D. In Table 1 agreement can be observed for the Mn oxidation states in S1 and S2 but is not possible at present for the So and S3 states. In this context the principle difference of the methods used should be mentioned.…”

“…Three distinct K-edge shifts of ca. 1 eV to higher energy were observed by Kusunoki et al [62] for the So-'S1, S, +S2 and S2pS3 transitions (see Fig. 9), indicating three successive oxidation steps of Mn up to S3.…”

Oxidation states of the manganese cluster during the flash-induced S-state cycle of the photosynthetic oxygen-evolving complex.

“…4) remains mostly unchanged at the S2 -> S3 transition. However, So, II, III, IV, IV or III, III, III, IV S1, III, III, IV, IV S2, III, IV, IV, IV S3, III, IV, IV, IV* In a previous paper (21) (11)(12)(13). The finding that the first and second flash induced similar shifts in the edge position (defined as halfheight energy, HHE) has led those authors to conclude that direct Mn oxidation takes place during both the Si -> S2 and S2 -> S3 transitions (11 …”

“…Mn Kedge spectra were measured for three sets of samples. Each set consisted of 2-4 samples given 0-5 flashes; in total a distribution of 7,8,12,8,6, and 8 samples given 0, 1, 2, 3, 4, and 5 flashes, respectively. The position of the main edge was characterized by its first IPE.…”

Water cleavage by solar radiation?an inspiring challenge of photosynthesis research

“…The arrangement &the manganese ions and their bridging ligands corresponds with a recent proposal of Yachandra et al (1993). It has to be emphasized that other models have been discussed where the bridging between the manganese ions of the binuclear groups is different (for a discussion, see Kusunoki et al 1992). The asymmetry of the protein environment is symbolized by differently hatched areas.…”