Thermodynamic parameters of 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 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.
Guerlesquin
F
F
Laboratoire de Chimie Bactérienne, CNRS, Marseille, France.
Sari
J C
JC
Bruschi
M
M
D002151:Calorimetry; D003574:Cytochrome c Group / Q000378:metabolism*; D003901:Desulfovibrio / Q000378:metabolism; D005288:Ferredoxins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D013816:Thermodynamics
D003574:Cytochrome c Group; D005288:Ferredoxins; C017165:cytochrome c(3)