Mar 13, 2014

The role of the high potential form of the cytochrome b559: Study of Thermosynechococcus elongatus mutants

Biochimica Et Biophysica Acta
Fernando GuerreroJosé M Ortega

Abstract

Cytochrome b559 is an essential component of the photosystem II reaction center in photosynthetic oxygen-evolving organisms, but its function still remains unclear. The use of photosystem II preparations from Thermosynechococcus elongatus of high integrity and activity allowed us to measure for the first time the influence of cytochrome b559 mutations on its midpoint redox potential and on the reduction of the cytochrome b559 by the plastoquinone pool (or QB). In this work, five mutants having a mutation in the α-subunit (I14A, I14S, R18S, I27A and I27T) and one in the β-subunit (F32Y) of cytochrome b559 have been investigated. All the mutations led to a destabilization of the high potential form of the cytochrome b559. The midpoint redox potential of the high potential form was significantly altered in the αR18S and αI27T mutant strains. The αR18S strain also showed a high sensitivity to photoinhibitory illumination and an altered oxidase activity. This was suggested by measurements of light induced oxidation and dark re-reduction of the cytochrome b559 showing that under conditions of a non-functional water oxidation system, once the cytochrome is oxidized by P680(+), the yield of its reduction by QB or the PQ pool was smalle...Continue Reading

  • References54
  • Citations8

References

Mentioned in this Paper

Synechococcus
Plastoquinol
Biochemical Pathway
Photopsia
Benzoquinone
Tissue Membrane
Carotene Measurement
Glycerin
Histidine
Oxygen Evolving Complex

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