Ortega J M, Hervás M, Losada M
Instituto de Bioquímica Vegetal y Fotosíntesis, Facultad de Biología, Universidad de Sevilla, Spain.
Eur J Biochem. 1988 Feb 1;171(3):449-55. doi: 10.1111/j.1432-1033.1988.tb13810.x.
The redox and acid/base states and midpoint potentials of cytochrome b-559 have been determined in oxygen-evolving photosystem II (PS II) particles at room temperature in the pH range from 6.5 to 8.5. At pH 7.5 the fresh PS II particles present about 2/3 of their cytochrome b-559 in its reduced and protonated (non-auto-oxidizable) high-potential form and about 1/3 in its oxidized and non-protonated low-potential form. Potentiometric reductive titration shows that the protonated high-potential couple is pH-independent (E'0, + 380 mV), whereas the low-potential couple is non-protonated and pH-independent above pH 7.6 (E'0, pH greater than 7.6, + 140 mV), but becomes pH-dependent below this pH, with a slope of -72 mV/pH unit. Moreover, evidence is presented that in PS II particles cytochrome b-559 can cycle, according to its established redox and acid/base properties, as an energy transducer at two alternate midpoint potentials and at two alternate pKa values. Red light absorbed by PS II induces reduction of cytochrome b-559 in these particles at room temperature, the reaction being completely blocked by dichlorophenyldimethylurea.
在室温下，于pH值6.5至8.5的范围内，测定了放氧型光系统II（PS II）颗粒中细胞色素b-559的氧化还原和酸碱状态以及中点电位。在pH 7.5时，新鲜的PS II颗粒中约2/3的细胞色素b-559处于还原且质子化（不可自氧化）的高电位形式，约1/3处于氧化且未质子化的低电位形式。电位滴定法表明，质子化的高电位对与pH无关（E'0，+ 380 mV），而低电位对在pH 7.6以上未质子化且与pH无关（E'0，pH大于7.6时，+ 140 mV），但在该pH以下变得与pH有关，斜率为-72 mV/pH单位。此外，有证据表明，在PS II颗粒中，细胞色素b-559可根据其既定的氧化还原和酸碱性质，作为能量转换器在两个交替的中点电位和两个交替的pKa值下循环。PS II吸收的红光在室温下会使这些颗粒中的细胞色素b-559还原，该反应完全被二氯苯基二甲基脲阻断。
