Hangarter R, Ort D R
Eur J Biochem. 1985 Jun 18;149(3):503-10. doi: 10.1111/j.1432-1033.1985.tb08953.x.
We have investigated the extent to which redox reactions of thylakoid membranes cooperate in ATP synthesis. This was done by measuring the onset of ATP synthesis following a series of single-turnover light-flashes at various levels of electron transport inhibition. In the presence of antibiotics that prevent the formation of a membrane potential, the onset of ATP synthesis seems to depend entirely on the formation of an adequately large delta pH. Under our conditions, the accumulation of about 60 mmol H+ X mol chlorophyll-1 is then necessary to form the requisite delta pH, which in turn requires about 15 saturating flashes in uninhibited thylakoid samples. Inhibition of some of the electron transfer centers by limiting the light intensity of the flashes, by dichlorophenyldimethylurea, by heat treatment, or by NH2OH-treatment caused an increase in the number of flashes required for the onset of ATP synthesis. The increase in the requisite number of flashes reflected the decreased number of electrons transferred in each flash, almost exactly the same number of electrons being transferred before ATP synthesis could begin. This effect of inhibitors was true when the two photosystems were operating in unison and when either of the two photosystems was acting alone. However, when either photosystem acted alone, there was an increase in the number of flashes required for the onset of ATP synthesis, an increase which was consistent with the observed lower flash-induced proton accumulation. A mathematical analysis of the onset of flash-induced ATP synthesis shows that at least several hundred proton-translocating electron transport complexes must be cooperating to form the threshold delta pH. In spite of this evidence for extensive cooperation among different electron transport complexes in ATP formation, the implied pooling of H+ ions does not seem to involve inner vesicle regions accessible to exogenous buffers. Thus, even when the number of H+ ions accumulated per flash was reduced by 70% through attenuation of the intensity of the flashes, exogenous hydrogen ion buffers present within the lumen of the thylakoid vesicle had no effect on the number of flashes required for the onset of ATP synthesis.
我们研究了类囊体膜的氧化还原反应在ATP合成过程中的协同程度。通过在不同水平的电子传递抑制条件下，测量一系列单周转光闪光后ATP合成的起始情况来进行此项研究。在存在阻止膜电位形成的抗生素的情况下，ATP合成的起始似乎完全取决于足够大的ΔpH的形成。在我们的实验条件下，积累约60 mmol H⁺/mol叶绿素⁻¹对于形成所需的ΔpH是必要的，而这反过来又需要在未受抑制的类囊体样品中进行约15次饱和闪光。通过限制闪光的光强度、二氯苯基二甲基脲、热处理或NH₂OH处理来抑制一些电子传递中心，会导致ATP合成起始所需的闪光次数增加。所需闪光次数的增加反映了每次闪光中转移的电子数量减少，在ATP合成开始之前转移的电子数量几乎完全相同。当两个光系统协同运作以及当两个光系统中的任何一个单独作用时，抑制剂的这种作用都是成立的。然而，当任何一个光系统单独作用时，ATP合成起始所需的闪光次数会增加，这种增加与观察到的较低的闪光诱导质子积累一致。对闪光诱导的ATP合成起始的数学分析表明，至少有几百个质子转运电子传递复合物必须协同作用才能形成阈值ΔpH。尽管有证据表明在ATP形成过程中不同电子传递复合物之间存在广泛的协同作用，但隐含的H⁺离子汇集似乎并不涉及外源缓冲液可进入的内囊泡区域。因此，即使通过减弱闪光强度使每次闪光积累的H⁺离子数量减少70%，类囊体囊泡腔内存在的外源氢离子缓冲液对ATP合成起始所需的闪光次数也没有影响。
