A New Value for the Redox Potential of Cytochrome c550 in Photosystem Ⅱ from Thermosynechococcus Elongatus
Cytochrome c550 (cyt c550), which is one of the extrinsic proteins of Photosystem Ⅱ (PSⅡ), is only present in cyanobacteria and red algae. Although this cytochrome has been reported to stabilize the binding of Ca2+ and Cl- ions, which are essential for activity of PSⅡ, the specific function of heme is not yet clear. The reported negative values of the midpoint redox potential (Em) of cyt c550 (-300 mV in the soluble state and -80 mV when associated with PSⅡ) appear to be incompatible with a redox function in PSⅡ. It has been reported that the Em of Qa in PSⅡ-enriched membranes was affected by the presence of redox mediators at low ambient potentials. We have carried out new measurements of Em of cyt c550 associated to PSⅡ changing the type and number of redox mediators used. We have determined that the Em of cyt c550 is about +200 mV in the absence of mediators or in the presence of a very limited number of mediators. Our results suggest that the highly reducing conditions reached in the presence of mediators, favor the reduction of a PSⅡ component, most likely the Mn cluster, thereby inducing alterations in protein, the heme environment and consequently the Em of the heme. The new value of Em of cyt c550 opens the possibility of a redox function for this protein.
Cytochrome c550 Photosystem Ⅱ Redox potential
Fernando Guerrero Arezki Sedoud Diana Kirilovsky A William Rutherford Mercedes Roncel José M Ortega
Institute de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, Américo Vespucio 49, 41 Commissariat a lEnergie Atomique, Institut de Biologie et Technologies de Saclay (iBiTec-S), 91191 Institute de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, Américo Vespucio 49, 41
国际会议
15th International Conference on Photosynthesis(第15届国际光合作用大会)
北京
英文
71-74
2010-08-22（万方平台首次上网日期，不代表论文的发表时间）