Redox potential of cytochrome c550 in the cyanobacterium Thermosynechococcus elongates |
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Authors: | Ishikita Hiroshi Knapp Ernst-Walter |
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Affiliation: | Institute of Chemistry, Department of Biology, Chemistry, and Pharmacy, Free University of Berlin, Takustrasse 6, D-14195 Berlin, Germany. |
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Abstract: | Cytochrome c550 (cyt c550) from photosystem II (PSII) exists in the PSII-bound form but can be released from PSII by treatment with divalent cations or Tris, yielding the isolated form. We calculated heme redox potentials (Em) based on the crystal structures of cyt c550 by solving the Poisson-Boltzmann equation. In the isolated form, the calculated Em are -240 mV at pH 6.0 and -352 mV at pH 9.0. This pH-dependence is predominantly due to deprotonation of the heme-propionic group near Asn-49. In the PSII-bound form, the calculated E(m) was up-shifted by 160 mV versus the isolated form due to a conformational change of protein backbone, yielding Em=-84 mV. |
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Keywords: | A. maxima, Arthrospira maxima cyt c550, cytochrome c550 Em, midpoint redox potential LPB equation, linearized Poisson-Boltzmann equation Mn-cluster, oxygen-evolving complex with Mn ions prop-A/prop-D, heme-propionic group A/D PSII, photosystem II S. 6803, Synechocystis PCC 6803 T. elongatus, Thermosynechococcus elongatus |
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