The mechanism for proton-coupled electron transfer from tyrosine in a model complex and comparisons with Y(Z) oxidation in photosystem II.

In the water-oxidizing reactions of photosystem II (PSII), a tyrosine residue plays a key part as an intermediate electron-transfer reactant between the primary donor chlorophylls (the pigment P(680)) and the water-oxidizing Mn cluster. The tyrosine is deprotonated upon oxidation, and the coupling between the proton reaction and electron transfer is of great mechanistic importance for the understanding of the water-oxidation mechanism. Within a programme on artificial photosynthesis, we have made and studied the proton-coupled tyrosine oxidation in a model system and been able to draw mechanistic conclusions that we use to interpret the analogous reactions in PSII.