Berg S P, Izawa S
Biochim Biophys Acta. 1977 May 11;460(2):206-19. doi: 10.1016/0005-2728(77)90207-9.
Three sites of silicomolybdate reduction in the electron transport chain of isolated tobacco chloroplasts are described. The relative participation of these sites is greatly influenced by the particular reaction conditions. One site (the only site when the reaction medium contains high concentrations of bovine serum albumin (greater than 5 mg/ml) is associated with Photosystem I, since it supports phosphorylation with a P/e2 value close to 1 and the reaction is totally sensitive to both plastocyanin inhibitors and 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Two other sites of silicomolybdate reduction are associated with Photosystem II. One site is 3-(3,4-dichlorophenyl)-1,1-dimethylurea insensitive and supports phosphorylation when the reaction mixture contains dimethyl sulfoxide and glycerol (protective agents). The P/e2 value routinely observed is about 0.2. Bovine serum albumin (1-2 mg/ml) can also act as a protective agent, but the efficiency of Photosystem II phosphorylation observed is lower. Silicomolybdate reduction supports virtually no phosphorylation, regardless of the reduction pathway, when the reaction mixture contains no protective agents. This is due to irreversible uncoupling by silicomolybdate itself. The silicomolybdate uncoupling is potentiated by high salt concentrations even if the presence of protective agents. Exposure of chloroplasts to silicomolybdate in the absence of protective agents rapidly inactivates both photosystems.
本文描述了分离的烟草叶绿体电子传递链中硅钼酸盐还原的三个位点。这些位点的相对参与程度受特定反应条件的极大影响。一个位点（当反应介质中含有高浓度牛血清白蛋白（大于5mg/ml）时为唯一的位点）与光系统I相关，因为它支持磷酸化，其P/e2值接近1，并且该反应对质体蓝素抑制剂和3-(3,4-二氯苯基)-1,1-二甲基脲均完全敏感。硅钼酸盐还原的另外两个位点与光系统II相关。一个位点对3-(3,4-二氯苯基)-1,1-二甲基脲不敏感，当反应混合物含有二甲基亚砜和甘油（保护剂）时支持磷酸化。通常观察到的P/e2值约为0.2。牛血清白蛋白（1-2mg/ml）也可作为保护剂，但观察到的光系统II磷酸化效率较低。当反应混合物不含保护剂时，无论还原途径如何，硅钼酸盐还原几乎不支持磷酸化。这是由于硅钼酸盐自身导致的不可逆解偶联。即使存在保护剂，高盐浓度也会增强硅钼酸盐的解偶联作用。在没有保护剂的情况下，叶绿体暴露于硅钼酸盐会迅速使两个光系统失活。
