Sequence of the redox changes of manganese and pattern of the changes of charges during water cleavage in photosynthesis.

Stable (> 0.5 s) quarternary oscillation of absorption changes of dark-adapted oxygen-evolving PS II particles was observed in the range of 350-384 nm through excitation with single flashes. The oscillation differs principally from that observed previously in the visible regions of the spectrum (Saygin and Witt, FEBS Lett. 176 (1984) 83-87 and FEBS Lett. 187 (1985) 224-226). While the patterns in the visible range are due to a new class of electrochromism indicating the change of charges of the water splitting complex, S (the sum of the changes of charges of the manganese center as well as of the bound, partly dissociated water), the pattern in the UV is due to the redox changes of the manganese (Dekker et al., Biochim. Biophys. Acta, 764 (1984) 301-309). With regard to the sequence in the four steps of water oxidation S 0 → S 1 , S 1 → S 2 , S 2 → S 3 , S 3 → S 0 , we observed in the UV twice the same absorption increase in the first two flashes; i.e., mainly with S 1 → S 2 and S 2 → S 3 , which was reversed in the 3rd flash; i.e., mainly with S 3 → S 0 . In the visible range we observed only one absorption increase in the 1st flash (S 1 → S 2 ), practically no change in the 2nd flash (S 2 → S 3 ), and a reverse in the 3rd flash (S 3 → S 0 ). At both wavelength regions the 4th flash showed practically no changes. Since the population of the four S-states becomes, however, progressively mixed from flash to flash, it is not possible to give on this basis only an unambiguous interpretation of the correlation between the S-states and the changes of charges and valence states of manganese. Using, however, low concentrations of hydroxylamine, this substance shifts by reduction the S-states backwards by two steps. Under these conditions one starts with the 2nd flash in state S 0 . Then we observed in the UV three times an absorption increase in the 2nd, 3rd and 4th flashes with a reverse direction in the 5th flash. From this it follows, without the use of any ambiguous correction procedures (for double hits and misses and initial S 0 /S 1 , ratio), that with the 1:1:1:1 Ch1 a 11 oxidation and electron extraction from S, respectively, the transition S 0 → S 1 → S 3 → S 0 is accompanied by a redox state change of manganese of +l:+l:+l:-3 and a total change of charges of 0: -1-1:0: -1. From the latter follows a pattern of 1:0:1:2 for the intrinsic proton release. Considering the 1st flash in the presence of NH 2 OH we observed a decrease of the electrochromic signal, which shows the formation of a negative charge. This indicates that in state S 0 at least one of the two water molecules is taken up in the dissociated form, OH - . The absorption increase induced through the 1st flash in the UV region in the presence of NH 2 OH may indicate the oxidation of a further manganese ion. In this case, in state S 0 , even both waters should be present in the dissociated form, OH - . However, this conclusion depends on the assumption that the change in the 1st flash is not induced predominantly by a one-electron event through parts of inactive PS II particles. On the basis of these results possible molecular configurations with regard to the manganese- and water state are outlined for S 0 → S 3 .