Cation Effects on the Electron-Acceptor Side of Photosystem II.

The journal of physical chemistry. B (2015-02-27)
Sahr Khan, Jennifer S Sun, Gary W Brudvig
RESUMEN

The normal pathway of electron transfer on the electron-acceptor side of photosystem II (PSII) involves electron transfer from quinone A, QA, to quinone B, QB. It is possible to redirect electrons from QA(-) to water-soluble Co(III) complexes, which opens a new avenue for harvesting electrons from water oxidation by immobilization of PSII on electrode surfaces. Herein, the kinetics of electron transfer from QA(-) to [Co(III)(terpy)2](3+) (terpy = 2,2';6',2″-terpyridine) are investigated with a spectrophotometric assay revealing that the reaction follows Michaelis-Menten saturation kinetics, is inhibited by cations, and is not affected by variation of the QA reduction potential. A negatively charged site on the stromal surface of the PSII protein complex, composed of glutamic acid residues near QA, is hypothesized to bind cations, especially divalent cations. The cations are proposed to tune the redox properties of QA through electrostatic interactions. These observations may thus explain the molecular basis of the effect of divalent cations like Ca(2+), Sr(2+), Mg(2+), and Zn(2+) on the redox properties of the quinones in PSII, which has previously been attributed to long-range conformational changes propagated from divalent cations binding to the Ca(II)-binding site in the oxygen-evolving complex on the lumenal side of the PSII complex.

MATERIALES
Referencia del producto
Marca
Descripción del producto

Sigma-Aldrich
Sucrose, for molecular biology, ≥99.5% (GC)
Sigma-Aldrich
Sucrose, ≥99.5% (GC)
Sigma-Aldrich
Sucrose, BioXtra, ≥99.5% (GC)
Sigma-Aldrich
Sucrose, BioUltra, for molecular biology, ≥99.5% (HPLC)
Sigma-Aldrich
Sucrose, ≥99.5%
Sigma-Aldrich
Sucrose, puriss., meets analytical specification of Ph. Eur., BP, NF
Sigma-Aldrich
Sucrose, ACS reagent
Sigma-Aldrich
Sucrose, BioReagent, suitable for cell culture, suitable for insect cell culture, ≥99.5% (GC)
Sigma-Aldrich
Sucrose, Grade II, suitable for plant cell culture
Sigma-Aldrich
Sucrose, meets USP testing specifications
Sigma-Aldrich
Sucrose, Grade I, suitable for plant cell culture