Electron transfer in the oxygen-evolving unit

The photosynthetically wasteful electron/hole recombination between P-bSO and Qa occurs with a half time of =100 /its [180], Thus efficient photosynthesis re- 

Kinetic parameters associated with several events in the water-splitting process 

While there is uncertainty as to whether Z is the immediate donor to P-680 in 02-evolving preparations, there is general agreement that Z is the immediate oxidant of the OEC manganese. Babcock et al. used time-resolved EPR to show that the reduction of Z is S-state dependent [198]. During the S2 — S3 and S3 — S4 

In the original formulation of the S-state model, Kok et al. postulated that the dark resting state of the OEC was a 3 1 mixture of S, and Sq, respectively [3]. This 

A number of PS II inhibitor treatments, such as Tris-washing and NH2OH extraction, had been well established as releasing Mn from the OEC [109]. Aker-lund, Andersson and co-workers showed that these treatments also released the peripheral polypeptides [71]. Mathis and co-workers showed that the ns phases in P-680 reduction that occur in untreated preparations are replaced by fxs components in inhibited samples [180]. The predominant decay phase is pH dependent, =2 ijs at pH 8 and =45 /is at pH 5, and is attributed to P-680 reduction by a secondary donor, usually designated D in optical work, which is identical to the EPR-detectable Z species [180,194,195]. The bulk pH and salt concentration dependencies of this phase implicate local membrane pH in influencing its time course 

---