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Temperature dependence of the high-spin S 2 to S 3 transition in Photosystem II: Mechanistic consequences

Temperature dependence of the high-spin S 2 to S 3 transition in Photosystem II: Mechanistic consequences

Alain Boussac

Biochim Biophys Acta Bioenerg. 2019 Jun 1;1860(6):508-518.

PMID: 31059676

Abstract:

The Mn4CaO5-cluster in Photosystem II advances through five oxidation states, S0 to S4, before water is oxidized and O2 is generated. The S2-state exhibits either a low-spin, S = 1/2 (S2LS), or a high-spin state, S = 5/2 (S2HS). Increasing the pH favors the S2HS configuration and mimics the formation of TyrZ in the S2LS-state at lower pH values (Boussac et al. Biochim. Biophys. Acta 1859 (2018) 342). Here, the temperature dependence of the S2HS to S3 transition was studied by EPR spectroscopy at pH 8.6. The present data strengthened the involvement of S2HS as a transient state in the S2LSTyrZ → S2HSTyrZ → S3TyrZ transition. Depending on the temperature, the S2HS progresses to S3 states exhibiting different EPR properties. One S3-state with a S = 3 signal, supposed to have a structure with the water molecule normally inserted in S2 to S3 transition, can be formed at temperatures as low as 77 K. This suggests that this water molecule is already bound in the S2HS state at pH 8.6. The nature of the EPR invisible S3 state, formed down to 4.2 K from a S2HS state, and that of the EPR detectable S3 state formed down to 77 K are discussed. It is proposed that in the S2LS to S3 transition, at pH < 8.6, the proton release (Sugiura et al. Biochim. Biophys. Acta 1859 (2018) 1259), the S2LS to S2HS conversion and the binding of the water molecule are all triggered by the formation of TyrZ.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP1052236868	(S)-5-Allyl-2-oxabicyclo[3.3.0]oct-8-ene		1052236-86-8	Price

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