Effects of temperature on the kinetics of the gated electron-transfer reaction between zinc cytochrome c and plastocyanin. Analysis of configurational fluctuation of the diprotein complex

Biochemistry
M M Ivković-Jensen, N M Kostić

Abstract

This is a study of the effects of temperature (in the range 273.3-307.7 K) and of ionic strength (in the range 2.5-100 mM) on the kinetics of photoinduced electron-transfer reaction 3Zncyt/pc(II)--> Zncyt+/pc(I) within the electrostatic complex of zinc cytochrome c and cupriplastocyanin at pH 7.0. In order to separate direct and indirect effects of temperature on the rate constants, viscosity of the solutions was fixed, at different values, by additions of sucrose. The activation parameters for the reaction within the preformed complex, at the low ionic strength, are delta H++ = 13 +/- 2 kJ/mol and delta S++ = -97 +/- 4 J/K mol. The activation parameters for the reaction within the encounter complex, at the higher ionic strength, are delta H++ = 13 +/- 1 kJ/mol and delta S++ = -96 +/- 3 J/K mol. Evidently, the two complexes are the same. The proteins associate similarly in the persistent and the transient complex, i.e., at different ionic strengths. In both complexes, however, electron transfer is gated by a rearrangement, as previous studies from this laboratory showed. Changes in the solution viscosity modulate this rearrangement by affecting delta H++, not delta S++. The activation parameters are analyzed by empirical method...Continue Reading

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Citations

May 4, 2005·Journal of Biological Inorganic Chemistry : JBIC : a Publication of the Society of Biological Inorganic Chemistry·S HirotaY Watanabe
May 12, 2004·Journal of Inorganic Biochemistry·Shun HirotaYoshihito Watanabe
Mar 15, 2002·Chemical Record : an Official Publication of the Chemical Society of Japan ... [et Al.]·S Hirota, O Yamauchi
Jan 3, 2013·IUBMB Life·Anna RauscherAndrás Málnási-Csizmadia
Sep 12, 2006·Journal of Inorganic Biochemistry·Shun HirotaYoshihito Watanabe
Jan 8, 2004·Journal of the American Chemical Society·Liu LiuMichael Y Ogawa

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