title: P680(+) reduction in oxygen-evolving Photosystem II core complexes.
abstract: The kinetics of P680(+) reduction in oxygen-evolving spinach Photosystem II (PS II) core particles were studied using both repetitive and single-flash 830 nm transient absorption. From measurements on samples in which PS II turnover is blocked, we estimate radical-pair lifetimes of 2 ns and 19 ns. Nanosecond single-flash measurements indicate decay times of 7 ns, 40 ns and 95 ns. Both the longer 40 ns and 95 ns components relate to the normal S-state controlled Yz → P680(+) electron transfer dynamics. Our analysis indicates the existence of a 7 ns component which provides evidence for an additional process associated with modified interactions involving the water-splitting catalytic site. Corresponding microsecond measurements show decay times of 4 μs and 90 μs with the possibility of a small component with a decay time of 20-40 μs. The precise origin of the 4 μs component remains uncertain but appears to be associated with the water-splitting center or its binding site while the 90 μs component is assigned to P680(+)-QA (-) recombination. An amplitude and kinetic analysis of the flash dependence data gives results that are consistent with the current model of the oxygen-evolving complex.
authors.affiliation: School of Physics, University of Sydney, 2006, NSW, Australia.
authors.forename: P B
authors.initials: PB
authors.lastname: Lukins
authors.forename: A
authors.initials: A
authors.lastname: Post
authors.forename: P J
authors.initials: PJ
authors.lastname: Walker
authors.forename: A W
authors.initials: AW
authors.lastname: Larkum