Thermodynamic parameters of the cytochrome c3-ferredoxin complex formation

The complex formation between cytochrome c3 and ferredoxin I from Desulfovibrio desulfuricans Norway was studied by microcalorimetric and pH-stat titration measurements. The stoichiometry of the complex was found to be one molecule of cytochrome c3 per monomer of ferredoxin I. The association consta...

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Bibliographic Details
Published in:Biochemistry (Easton) 1987-11, Vol.26 (23), p.7438-7443
Main Authors: Guerlesquin, Francoise, Sari, Jean Claude, Bruschi, Mireille
Format: Article
Language:English
Subjects:
Biological and medical sciences
Calorimetry
Cytochrome c Group - metabolism
Desulfovibrio - metabolism
Desulfovibrio desulfuricans
Ferredoxins - metabolism
Fundamental and applied biological sciences. Psychology
Hydrogen-Ion Concentration
Interactions. Associations
Intermolecular phenomena
Kinetics
Molecular biophysics
Thermodynamics
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Summary:The complex formation between cytochrome c3 and ferredoxin I from Desulfovibrio desulfuricans Norway was studied by microcalorimetric and pH-stat titration measurements. The stoichiometry of the complex was found to be one molecule of cytochrome c3 per monomer of ferredoxin I. The association constant determined at T = 283 K in tris(hydroxymethyl)aminomethane hydrochloride (Tris-HCl) buffer, 10(-2) M and pH 7.7, was KA = 1.3 X 10(6) M-1. Though the enthalpy (delta H = 19 +/- 1 kJ.mol-1) and the entropy (delta S = 183 J.K-1.mol-1) were positive and consistent with a hydrophobic process involved in the interaction, the analysis of ionic strength dependence exhibited an important electrostatic effect on the association. The use of both Tris-HCl and phosphate buffers during microcalorimetric experiments showed proton release at pH 6.6. The pH-stat study of proton release indicated that one of the charged groups involved in the interacting site underwent a pK shift from 7.35 to 6.05.
ISSN:0006-2960
1520-4995
DOI:10.1021/bi00397a036