Metallo-radical hypothesis for photoassembly of (Mn)4-cluster of photosynthetic oxygen evolving complex

A new hypothetical mechanism is proposed for photoassembly of the (Mn)(4)-cluster of the photosynthetic oxygen evolving complex (OEC). In this process, a neutral radical of Y-Z tyrosine plays a role in oxidizing Mn2+ associated with an apo-OEC, and also in abstracting a proton from a water molecule bound to the Mn2+ ion, together with D1-His190. This is in a similar fashion to the metallo-radical mechanism proposed for photosynthetic water oxidation by the (Mn)(4)-cluster. The model insists that a common mechanism participates in the photoassembly of the (Mn)4-cluster and the photosynthetic water oxidation. (C) 2001 Elsevier Science B.V. All rights reserved.