Kinetics of static and diffusive electron transfer between zinc-substituted cytochrome c and plastocyanin. Indications of nonelectrostatic interactions between highly charged metalloproteins

Cupriplastocyanin, pc(II), quenches the triplet state of zinc cytochrome c, super(3)Zn(cyt), by electron transfer as shown in Scheme I. All the experiments are done at pH 7.0. Nonredox modes of quenching are ruled out by detection of the cation radical Zn(cyt) super(+) and by experiments in which re...

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Veröffentlicht in:Journal of the American Chemical Society 1991-07, Vol.113 (16), p.6067-6073
Hauptverfasser: Zhou, Jian S, Kostic, Nenad M
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Sprache:eng
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Zusammenfassung:Cupriplastocyanin, pc(II), quenches the triplet state of zinc cytochrome c, super(3)Zn(cyt), by electron transfer as shown in Scheme I. All the experiments are done at pH 7.0. Nonredox modes of quenching are ruled out by detection of the cation radical Zn(cyt) super(+) and by experiments in which redox quenching is precluded. At the ionic strengths of 0.100 M and higher, the electron-transfer reaction occurs bimolecularly, via the encounter complex super(3)Zn(cyt)/pc(II); k sub(f) = (2.8 plus or minus 0.6) x 10 super(5)/s, and the equilibrium constant K sub(a) depends on ionic strength. At he ionic strengths of 10 mM and lower, the reaction can be made to occur predominantly unimolecularly, within the preformed complex super(3)Zn(cyt)/pc(II); k sub(F) = (2.5 plus or minus 0.4) x 10 super(5)/s within super(3)Zn(cyt)/pc(II), and k sub(B) = (1.1 plus or minus 0.5)x 10 super( )5/s within Zn(cyt) super(+)/pc(I).
ISSN:0002-7863
1520-5126
DOI:10.1021/ja00016a021