title: A hydrogen-atom abstraction model for the function of YZ in photosynthetic oxygen evolution.
abstract: Recent magnetic-resonance work on YŻ 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 YŻ functions to abstract hydrogen atoms from aquo- and hydroxy-bound managanese 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/YZ center forms a single catalytic center that comprises the Oxygen Evolving Complex in Photosystem II.
authors.affiliation: Department of Chemistry, Michigan State University, 48824, East Lansing, MI, USA.
authors.forename: C W
authors.initials: CW
authors.lastname: Hoganson
authors.forename: N
authors.initials: N
authors.lastname: Lydakis-Simantiris
authors.forename: X S
authors.initials: XS
authors.lastname: Tang
authors.forename: C
authors.initials: C
authors.lastname: Tommos
authors.forename: K
authors.initials: K
authors.lastname: Warncke
authors.forename: G T
authors.initials: GT
authors.lastname: Babcock
authors.forename: B A
authors.initials: BA
authors.lastname: Diner
authors.forename: J
authors.initials: J
authors.lastname: McCracken
authors.forename: S
authors.initials: S
authors.lastname: Styring