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 class="mathematics"> data-equation-construct="true" class="math-equation-construct"> data-equation-image="true" class="math-equation-image"> alt="math formula" src="http://onlinelibrary.wiley.com/store/10.1016/0014-5793(90)81194-S/asset/equation/feb2001457939081194s-math-si1.gif?v=1&s=01874350fedb09abdca07e9cf28f05d5b35ffb1a" class="inlineGraphic" /> data-equation-mathml="true" class="math-equation-mathml" style="display:none"> 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 class="mathematics"> data-equation-construct="true" class="math-equation-construct"> data-equation-image="true" class="math-equation-image"> alt="math formula" src="http://onlinelibrary.wiley.com/store/10.1016/0014-5793(90)81194-S/asset/equation/feb2001457939081194s-math-si2.gif?v=1&s=08caf4217f25475777fa6943201f018bbb5372ff" class="inlineGraphic" /> data-equation-mathml="true" class="math-equation-mathml" style="display:none"> cm−1.