A hydrogen-atom abstraction model for the function of Y-Z in photosynthetic oxygen evolution

• Recent magnetic-resonance work on Y-Z suggests that this species exhibits considerable motional flexibility in its functional site and that its phenol oxygen is not involved in a well-ordered hydrogen-bond interaction (Tang et al., submitted; Tommos et al., in press). Both of these observations are inconsistent with a simple electron-transfer function for this radical in photosynthetic water oxidation. By considering the roles of catalytically active amino acid radicals in other enzymes and recent data on the water-oxidation process in Photosystem II, we rationalize these observations by suggesting that Y-Z functions to abstract hydrogen atoms from aquo- and hydroxy-bound manganese ions in the (Mn)(4) cluster on each S-state transition. The hydrogen-atom abstraction process may occur either by sequential or concerted kinetic pathways. Within this model, the (Mn)(4)/Y-Z center forms a single catalytic center that comprises the Oxygen Evolving Complex in Photosystem II.

Ämnesord

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

Nyckelord

electron paramagnetic resonance

manganese cluster

oxygen evolution

oxygen evolving complex

Photosystem II

proton transfer

tyrosine radical

water oxidation

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art (ämneskategori)

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