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A high redox potential form of cytochrome c550 in Photosystem II from Thermosynechococcus elongatus

AuthorsGuerrero, Fernando ; Sedoud, Arezki; Kirilovsky, D.; Rutherford, A. William; Ortega, José M. ; Roncel Gil, Mercedes
Issue DateFeb-2011
PublisherAmerican Society for Biochemistry and Molecular Biology
CitationJournal of biological chemistry 286 (8): 5985-5994 (2011).
AbstractCytochrome c550 (cyt c550) is a component of photosystem II (PSII) from cyanobacteria, red algae, and some other eukaryotic algae. Its physiological role remains unclear. In the present work, measurements of the midpoint redox potential (Em) were performed using intact PSII core complexes preparations from a histidine-tagged PSII mutant strain of the thermophilic cyanobacterium Thermosynechococcus (T.) elongatus. When redox titrations were done in the absence of redox mediators, an Em value of +200 mV was obtained for cyt c550. This value is ∼300 mV more positive than that previously measured in the presence of mediators (Em = −80 mV). The shift from the high potential form (Em = +200 mV) to the low potential form (Em = −80 mV) of cyt c550 is attributed to conformational changes, triggered by the reduction of a component of PSII that is sequestered and out of equilibrium with the medium, most likely the Mn4Ca cluster. This reduction can occur when reduced low potential redox mediators are present or under highly reducing conditions even in the absence of mediators. Based on these observations, it is suggested that the Em of +200 mV obtained without mediators could be the physiological redox potential of the cyt c550 in PSII. This value opens the possibility of a redox function for cyt c550 in PSII.
DescriptionThis research was originally published in Journal of Biological Chemistry. Fernando Guerrero, Arezki Sedoud, Diana Kirilovsky, A. William Rutherford, José M. Ortega, and Mercedes Roncel. A High Redox Potential Form of Cytochrome c550 in Photosystem II from Thermosynechococcus elongatus. Journal of Biological Chemistry. 2011. Vol 286: 5985-5994. © the American Society for Biochemistry and Molecular Biology
Publisher version (URL)http:dx.doi.org/10.1074/jbc.M110.170126
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