May 12, 2011

Two tyrosines that changed the world: Interfacing the oxidizing power of photochemistry to water splitting in photosystem II

Biochimica Et Biophysica Acta
Stenbjörn StyringFikret Mamedov


Photosystem II (PSII), the thylakoid membrane enzyme which uses sunlight to oxidize water to molecular oxygen, holds many organic and inorganic redox cofactors participating in the electron transfer reactions. Among them, two tyrosine residues, Tyr-Z and Tyr-D are found on the oxidizing side of PSII. Both tyrosines demonstrate similar spectroscopic features while their kinetic characteristics are quite different. Tyr-Z, which is bound to the D1 core protein, acts as an intermediate in electron transfer between the primary donor, P(680) and the CaMn₄ cluster. In contrast, Tyr-D, which is bound to the D2 core protein, does not participate in linear electron transfer in PSII and stays fully oxidized during PSII function. The phenolic oxygens on both tyrosines form well-defined hydrogen bonds to nearby histidine residues, His(Z) and His(D) respectively. These hydrogen bonds allow swift and almost activation less movement of the proton between respective tyrosine and histidine. This proton movement is critical and the phenolic proton from the tyrosine is thought to toggle between the tyrosine and the histidine in the hydrogen bond. It is found towards the tyrosine when this is reduced and towards the histidine when the tyrosine is o...Continue Reading

Mentioned in this Paper

Biochemical Pathway
Photosynthetic Reaction Centers
Thylakoid Membrane
Oxygen Evolving Complex
Enzymes, antithrombotic
Amino Acids, I.V. solution additive

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