Allakhverdiev S I, Klimov V V, Carpentier R
Centre de Recherche en Photobiophysique, Université du Québec à Trois-Rivières, PQ, Canada.
Proc Natl Acad Sci U S A. 1994 Jan 4;91(1):281-5. doi: 10.1073/pnas.91.1.281.
In photosynthetic systems, the absorbed light energy is used to generate electron transport or it is lost in the form of fluorescence and thermal emission. While fluorescence can be readily measured, the detection of thermal deactivation processes can be achieved by the photoacoustic technique. In that case, the pressure wave generated by the thermal deactivations in a sample irradiated with modulated light is detected by a sensitive microphone. The relationships between the yield of fluorescence and thermal emissions measured simultaneously were analyzed by using a spinach photosystem II (PSII)-enriched preparation. It is shown that the quenching of fluorescence due to the photochemical activity of the preparations (photochemical quenching) increases in proportion to the fraction of thermal deactivations that is not immediately released as heat but is stored in photochemical intermediates (energy-storage yield) as the intensity of the photoacoustic modulated measuring beam (35 Hz) is decreased. Maximal levels of fluorescence and thermal emissions were both decreased in similar proportions upon photoreduction of pheophytin (Pheo), the primary acceptor of PSII. The variable components of fluorescence and thermal emissions were strongly decreased upon depletion of Mn from the Mn complex that catalyzes water oxidation and were recovered proportionally during reconstitution with Mn2+ at various Mn2+/reaction center ratios. Finally, depletion of Mn from the Mn complex together with the Fe of the QA-Fe-QB complex that is composed of the secondary quinone acceptors of PSII resulted in an increased initial level of fluorescence Fo and in the loss of the variable components of fluorescence and thermal emissions. The initial Fo and the variable components could be partially recovered by reconstitution of both donor and acceptor sides with Mn2+, Co2+, HCO3- and plastoquinone. It is concluded that the photochemical fluorescence quenching is correlated with a simultaneous "quenching" of a variable component of thermal emission. It is proposed that the measured component of variable thermal emission is related to the decay of the pair [P680+ Pheo-]. The suggestion is also made that a bicarbonate-induced protonation of reduced QA or QB or conformational change in the PSII complex, or both, adds an additional entropic factor to the variable thermal emission component.
在光合系统中，吸收的光能用于产生电子传递，或者以荧光和热发射的形式损失掉。虽然荧光很容易测量，但热失活过程的检测可以通过光声技术来实现。在这种情况下，由调制光照射的样品中的热失活产生的压力波由灵敏的麦克风检测。使用富含菠菜光系统II（PSII）的制剂分析了同时测量的荧光产率和热发射之间的关系。结果表明，由于制剂的光化学活性导致的荧光猝灭（光化学猝灭）与热失活的部分成正比增加，热失活不是立即以热的形式释放，而是作为光化学中间体存储（能量存储产率），随着光声调制测量光束（35Hz）强度的降低。PSII的初级受体脱镁叶绿素（Pheo）光还原后，荧光和热发射的最大水平均以相似的比例降低。在催化水氧化的锰复合物中锰耗尽后，荧光和热发射的可变成分强烈降低，并在以各种Mn2+/反应中心比率用Mn2+重构期间成比例地恢复。最后，从锰复合物中耗尽锰以及由PSII的次级醌受体组成的QA-Fe-QB复合物中的铁，导致荧光初始水平Fo增加以及荧光和热发射可变成分的损失。通过用Mn2+、Co2+、HCO3-和质体醌重构供体和受体两侧，可以部分恢复初始Fo和可变成分。得出的结论是，光化学荧光猝灭与热发射可变成分的同时“猝灭”相关。有人提出，测量的可变热发射成分与[P680+ Pheo-]对的衰减有关。还提出，还原的QA或QB的碳酸氢盐诱导的质子化或PSII复合物中的构象变化，或两者兼而有之，为可变热发射成分增加了额外的熵因素。
