Biggins J
Biochim Biophys Acta. 1978 Nov 9;504(2):288-97. doi: 10.1016/0005-2728(78)90177-9.
The photoinduced turnover of P-700 (the reaction center chlorophyll a of photosystem I) in higher plant thylakoids was examined at room temperature by observation of the kinetics and amplitude of the transmission signal at 700 nm. The concentration of P-700 functional in cyclic and non-cyclic electron transfer reactions was compared. For the cyclic reactions mediated by N-methylphenazonium-p-methosulfate, 2,3,5,6-tetramethylphenylenediamine, 2,6-dichlorophenolindophenol and N,N,N',N'-tetramethylphenylenediamine and non-cyclic reactions utilizing either methylviologen or NADP+ as acceptor, the illuminated steady-state concentration of P-700+ was shown to be similar. The data support the concept of a homogeneous pool of P-700 that is capable of interaction in both cyclic and non-cyclic electron transfer reactions and are consistent with previous data obtained in vivo. The amplitude and kinetics of the P-700 signal were found to be very dependent upon the composition of the reaction medium and differences were noted for turnover in the cyclic and non-cyclic reactions. Specifically, at white light saturation, the addition of low concentrations of divalent cations, such as Mg2+ or Ca2+, had no effect on the signal amplitude during cyclic reactions, but, in confirmation of previous work, caused an attenuation of the signal amplitude during non-cyclic flow. At low light intensities, the divalent cations caused a similar reduction in redox level of P-700 in the steady-state during non-cyclic flow and also reduced the rate of P-700 photooxidation in the cyclic reactions. The concentration of divalent cation that reduced the signal amplitude of P-700+ during non-cyclic flow was compared with that required for the stimulation of the variable component of fluorescence, and it was shown to be similar with half maximal effects at 1 mM Mg+. The observations confirm that divalent cations control non-cyclic electron transport by an activation of Photosystem II in addition to regulating the distribution of excitation energy between the two photosystems.
通过观察700 nm处传输信号的动力学和幅度，在室温下检测了高等植物类囊体中光诱导的P - 700（光系统I的反应中心叶绿素a）周转情况。比较了在循环和非循环电子传递反应中起作用的P - 700的浓度。对于由硫酸对甲氧基N - 甲基吩嗪鎓、2,3,5,6 - 四甲基苯二胺、2,6 - 二氯酚靛酚和N,N,N',N' - 四甲基苯二胺介导的循环反应以及利用甲基紫精或NADP⁺作为受体的非循环反应，光照下P - 700⁺的稳态浓度显示相似。这些数据支持了P - 700形成均一库的概念，该库能够参与循环和非循环电子传递反应，并且与之前在体内获得的数据一致。发现P - 700信号的幅度和动力学非常依赖于反应介质的组成，并且在循环和非循环反应的周转中观察到差异。具体而言，在白光饱和时，添加低浓度的二价阳离子，如Mg²⁺或Ca²⁺，对循环反应期间的信号幅度没有影响，但正如之前的工作所证实的，会导致非循环流动期间信号幅度的衰减。在低光强度下，二价阳离子在非循环流动的稳态期间导致P - 700的氧化还原水平有类似的降低，并且也降低了循环反应中P - 700光氧化的速率。将在非循环流动期间降低P - 700⁺信号幅度的二价阳离子浓度与刺激荧光可变组分所需的浓度进行比较，结果表明在1 mM Mg⁺时半最大效应相似。这些观察结果证实，二价阳离子除了调节两个光系统之间的激发能分布外，还通过激活光系统II来控制非循环电子传递。
