Characterization by FTIR spectroscopy of the photoreduction of the primary quinone acceptor QA in photosystem II

[摘要]

Molecular changes associated with the photoreduction of the primary quinone acceptor Q_a of photosystem II have been characterized by Fourier transform infrared spectroscopy. This reaction was light-induced at room temperature on photosystem II membranes in the presence of hydroxylamine and diuron. A positive signal at 1478 cm⁻¹ is assigned to the C⋯O stretching mode of the semiquinone anion, and can be correlated to the negative C=O mode(s) of the neutral Q_A at 1645 cm⁻¹ and/or 16 cm⁻¹. Analogies with bacterial reaction center are found in the amide I absorption range at 1672 cm⁻¹, 1653 cm⁻¹ and 1630 cm⁻¹. The stabilization of Q_A ⁻ does not result from a large protein conformation change, but involves perturbations of several amino acid vibrations. At 1658 cm⁻¹, a negative feature sensitive to ¹H–²H exchange is tentatively assigned to a δNH₂ histidine mode, while tryptophan D₂252 could contribute to the signal at cm⁻¹.

[学科分类] 生物化学/生物物理

[关键词] Fourier transform infrared difference spectroscopy;Photosystem II;Primary quinone acceptor;Plastoquinone;FTIR;Fourier transform infrared;PS II;photosystem II;RC;reaction center;Rps.;Rhodopseudomonas;Rb.;Rhodobacter;QA;primary quinone acceptor;P680;primary electron donor;BBY;PS II-enriched membranes;Mes;2-(N-morpholino)ethanesulphonic acid;Tris;tris(hydroxymethyl)aminomethane;DCMU;diuron;3-(3;4dichlorophenyl)-1;1-dimethylurea;Chl;chlorophyll;Tyrz;secondary electron donor tyrosine D1161;PQ-9;plastoquinone-9;3-MBQ;trimethylbenzoquinone;THF;tetrahydrofuran