In this section
@article{Ishida:2008:10.1074/jbc.M710583200,
author = {Ishida, N and Sugiura, M and Rappaport, F and Lai, TL and Rutherford, AW and Boussac, A},
doi = {10.1074/jbc.M710583200},
journal = {J Biol Chem},
pages = {13330--13340},
title = {Biosynthetic exchange of bromide for chloride and strontium for calcium in the photosystem II oxygen-evolving enzymes.},
url = {http://dx.doi.org/10.1074/jbc.M710583200},
volume = {283},
year = {2008}
}
TY - JOUR
AB - The active site for water oxidation in photosystem II goes through five sequential oxidation states (S(0) to S(4)) before O(2) is evolved. It consists of a Mn(4)Ca cluster close to a redox-active tyrosine residue (Tyr(Z)). Cl(-) is also required for enzyme activity. To study the role of Ca(2+) and Cl(-) in PSII, these ions were biosynthetically substituted by Sr(2+) and Br(-), respectively, in the thermophilic cyanobacterium Thermosynechococcus elongatus. Irrespective of the combination of the non-native ions used (Ca/Br, Sr/Cl, Sr/Br), the enzyme could be isolated in a state that was fully intact but kinetically limited. The electron transfer steps affected by the exchanges were identified and then investigated by using time-resolved UV-visible absorption spectroscopy, time-resolved O(2) polarography, and thermoluminescence spectroscopy. The effect of the Ca(2+)/Sr(2+) and Cl(-)/Br(-) exchanges was additive, and the magnitude of the effect varied in the following order: Ca/Cl < Ca/Br < Sr/Cl < Sr/Br. In all cases, the rate of O(2) release was similar to that of the S(3)Tyr(Z)(.) to S(0)Tyr(Z) transition, with the slowest kinetics (i.e. the Sr/Br enzyme) being approximately 6-7 slower than in the native Ca/Cl enzyme. This slowdown in the kinetics was reflected in a decrease in the free energy level of the S(3) state as manifest by thermoluminescence. These observations indicate that Cl(-) is involved in the water oxidation mechanism. The possibility that Cl(-) is close to the active site is discussed in terms of recent structural models.
AU - Ishida,N
AU - Sugiura,M
AU - Rappaport,F
AU - Lai,TL
AU - Rutherford,AW
AU - Boussac,A
DO - 10.1074/jbc.M710583200
EP - 13340
PY - 2008///
SN - 0021-9258
SP - 13330
TI - Biosynthetic exchange of bromide for chloride and strontium for calcium in the photosystem II oxygen-evolving enzymes.
T2 - J Biol Chem
UR - http://dx.doi.org/10.1074/jbc.M710583200
VL - 283
ER -
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