Institute of Plant Physiology, Russian Academy of Sciences, Moscow 127276, Russia.
Proc Natl Acad Sci U S A. 2011 May 10;108(19):8054-8. doi: 10.1073/pnas.1100173108. Epub 2011 Apr 26.
In a previous study, we measured the redox potential of the primary electron acceptor pheophytin (Phe) a of photosystem (PS) II in the chlorophyll d-dominated cyanobacterium Acaryochloris marina and a chlorophyll a-containing cyanobacterium, Synechocystis. We obtained the midpoint redox potential (E(m)) values of -478 mV for A. marina and -536 mV for Synechocystis. In this study, we measured the redox potentials of the primary electron acceptor quinone molecule (Q(A)), i.e., E(m)(Q(A)/Q(A)(-)), of PS II and the energy difference between [P680·Phe a(-)·Q(A)] and [P680·Phe a·Q(A)(-)], i.e., ΔG(PhQ). The E(m)(Q(A)/Q(A)(-)) of A. marina was determined to be +64 mV without the Mn cluster and was estimated to be -66 to -86 mV with a Mn-depletion shift (130-150 mV), as observed with other organisms. The E(m)(Phe a/Phe a(-)) in Synechocystis was measured to be -525 mV with the Mn cluster, which is consistent with our previous report. The Mn-depleted downshift of the potential was measured to be approximately -77 mV in Synechocystis, and this value was applied to A. marina (-478 mV); the E(m)(Phe a/Phe a(-)) was estimated to be approximately -401 mV. These values gave rise to a ΔG(PhQ) of -325 mV for A. marina and -383 mV for Synechocystis. In the two cyanobacteria, the energetics in PS II were conserved, even though the potentials of Q(A)(-) and Phe a(-) were relatively shifted depending on the special pair, indicating a common strategy for electron transfer in oxygenic photosynthetic organisms.
在之前的研究中，我们测量了叶绿素 d 占主导地位的蓝藻 Acaryochloris marina 和含有叶绿素 a 的蓝藻 Synechocystis 中光系统 II（PS II）的原初电子受体叶绿素 a 衍生物（Phe）a 的氧化还原电势。我们得到了 A. marina 的中点氧化还原电势（E(m)）值为-478 mV，Synechocystis 的 E(m)值为-536 mV。在这项研究中，我们测量了 PS II 的原初电子受体醌分子（Q(A)）的氧化还原电势，即 E(m)(Q(A)/Q(A)(-))，以及 [P680·Phe a(-)·Q(A)] 和 [P680·Phe a·Q(A)(-)] 之间的能量差，即 ΔG(PhQ)。在没有锰簇的情况下，A. marina 的 E(m)(Q(A)/Q(A)(-))被确定为+64 mV，并且随着锰簇的耗竭，E(m)(Q(A)/Q(A)(-))估计为-66 至-86 mV（130-150 mV），与其他生物体观察到的情况一致。在有锰簇的情况下，Synechocystis 的 E(m)(Phe a/Phe a(-))被测量为-525 mV，这与我们之前的报告一致。在 Synechocystis 中，测量到了电位的锰耗竭向下移动约-77 mV，该值应用于 A. marina（-478 mV）；E(m)(Phe a/Phe a(-))估计约为-401 mV。这些值导致 A. marina 的 ΔG(PhQ)为-325 mV，Synechocystis 的 ΔG(PhQ)为-383 mV。在这两种蓝藻中，即使 Q(A)(-)和 Phe a(-)的电位根据特殊对相对移动，PS II 的能量仍然是保守的，这表明含氧光合作用生物中电子转移的共同策略。
