Time-resolved oxygen production by PSII: chasing chemical intermediates

Autor(en): Clausen, J
Debus, RJ
Junge, W 
Stichwörter: A-B LOOP; ABSORPTION CHANGES; activation energy; Biochemistry & Molecular Biology; Biophysics; CRYSTAL-STRUCTURE; ELECTRON-TRANSFER; EVOLVING COMPLEX; II D1 PROTEIN; MANGANESE CLUSTER; photosynthesis; PHOTOSYNTHETIC WATER OXIDATION; photosystem II; PHOTOSYSTEM-II; REDOX TRANSITIONS; S-state; water oxidation
Erscheinungsdatum: 2004
Herausgeber: ELSEVIER
Journal: BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS
Volumen: 1655
Ausgabe: 1-3
Startseite: 184
Seitenende: 194
Zusammenfassung: 
Photosystem II (PSII) produces dioxygen from water in a four-stepped process, which is driven by four quanta of light and catalysed by a Mn-cluster and tyrosine Z. Oxygen is liberated during one step, coined S-3 double right arrow S-0. Chemical intermediates on the way from reversibly bound water to dioxygen have not yet been tracked, however, a break in the Arrhenius plot of the oxygen-evolving step has been taken as evidence for its existence. We scrutinised the temperature dependence of (i) UV-absorption transients attributable to the reduction of the Mn-cluster and tyrosine Z by water, and (ii) polarographic transients attributable to the release of dioxygen. Using a centrifugatable and kinetically competent Pt-electrode, we observed no deviation from a linear Arrhenius plot of oxygen release in the temperature range from -2 to 32 degreesC, and hence no evidence, by this approach, for a sufficiently long-lived chemical intermediate. The half-rise times of oxygen release differed between Synechocystis WT* (at 20 degreesC: 1.35 ms) and a point mutant (D1-D61N: 13.1 ms), and the activation energies differed between species (Spinacia oleracea, 30 kJ/mol versus Synechocystis, 41 kJ/mol) and preparations (PSII membranes, 41 kJ/moI versus core complexes, 33 kJ/ mol, Synechocystis). Correction for polarographic artefacts revealed, for the first time, a temperature-dependent lag-phase of the polarographic transient (duration at 20 degreesC: 0.45 ms, activation energy: 31 kJ/mol), which was indicative of a short-lived intermediate. It was, however, not apparent in the UV-transients. Thus the ``intermediate'' was probably newly formed and transiently bound oxygen. (C) 2004 Elsevier B.V. All rights reserved.
ISSN: 00052728
DOI: 10.1016/j.bbabio.2003.06.001

Show full item record

Google ScholarTM

Check

Altmetric