Ca2+ determines the entropy changes associated with the formation of transition states during wateroxidation by Photosystem II†,10.1039/C1EE01408K

热搜：

Lactoyl-CoA 全氟丁基戊烷白叶藤碱全氟己基辛烷新白叶藤碱壳寡糖特色专题-生物多肽

Ca2+ determines the entropy changes associated with the formation of transition states during wateroxidation by Photosystem II†

Fabrice Rappaport,Naoko Ishida,Miwa Sugiura,Alain Boussac

Energy & Environmental Science Pub Date : 05/26/2011 00:00:00 , DOI:10.1039/C1EE01408K

Abstract

The role of Ca²⁺ in the Photosystem IIwater oxidation mechanism has been investigated in the higher redox states of the enzyme. The involvement of Ca²⁺ in structuring the environment of the tyrosine Y_Z in the S₃ state has been investigated by studying the effect of a Ca/Sr exchange by pulse-EPR spectroscopy. It is shown that Ca and Yz are involved in a common hydrogen bond network in S₃. The comparison of the temperature dependence of the rate of the water oxidation reaction shows that the slowdown of the S₃Y_Z˙ → S₀ transition in Sr-PSII mainly arises from a decrease of the entropic part of the ΔG^# of the reaction. This suggests that Ca/Sr exchange perturbs the distribution of the conformational microstates and thereby hinders the overall water splitting process.