Ghanotakis D F, Babcock G T, Yerkes C T
Arch Biochem Biophys. 1983 Aug;225(1):248-55. doi: 10.1016/0003-9861(83)90027-9.
The conditions for steady-state Signal IIf formation in response to single turnover flashes in Tris-treated, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)-inhibited chloroplasts have been investigated. DCMU inhibits Signal IIf generation as the photoinactive state, Z P680 Q-A, accumulates. Potassium ferricyanide relieves this inhibition so that Signal IIf can be fully developed on each flash in a flash series. The effectiveness of ferricyanide in stimulating Signal IIf formation is dependent on its concentration, the flash repetition rate, and the salt composition of the chloroplast suspension. There are two models in the literature for Q-A oxidation under these inhibitory conditions: direct oxidation of Q-A by exogenous acceptors like ferricyanide or oxidation of Q-A by an endogenous acceptor, AH, which has a midpoint potential of approximately 400 mV. It is found that the direct exogenous acceptor model accounts well for these data, whereas the AH model does not explain several of these results. The apparent rate constant for the direct oxidation of Q-A by ferricyanide at various concentrations of salt has been calculated from our electron paramagnetic resonance (EPR) data and compared with the corresponding rate constant determined by S. Itoh from fluorescence data (Biochim, Biophys. Acta 504, 324-340, 1978); good agreement is found for the two different experimental approaches.
研究了在经三羟甲基氨基甲烷（Tris）处理且受3-(3,4-二氯苯基)-1,1-二甲基脲（DCMU）抑制的叶绿体中，单次周转闪光响应下稳态信号IIf形成的条件。随着光无活性状态Z P680 Q-A的积累，DCMU抑制信号IIf的产生。铁氰化钾可缓解这种抑制作用，从而使信号IIf在闪光系列中的每次闪光时都能充分发展。铁氰化钾刺激信号IIf形成的有效性取决于其浓度、闪光重复率以及叶绿体悬浮液的盐组成。在这些抑制条件下，文献中有两种关于Q-A氧化的模型：Q-A被铁氰化钾等外源受体直接氧化，或Q-A被中点电位约为400 mV的内源受体AH氧化。研究发现，直接外源受体模型能很好地解释这些数据，而AH模型无法解释其中的几个结果。已根据我们的电子顺磁共振（EPR）数据计算出不同盐浓度下铁氰化钾直接氧化Q-A的表观速率常数，并与S. Itoh从荧光数据中确定的相应速率常数进行了比较（《生物化学与生物物理学报》504, 324 - 340, 1978）；两种不同的实验方法结果吻合良好。
