title: Kinetics and thermodynamics of copper(II) binding to apoazurin.
abstract: The binding of copper(II) to apoazurin has been probed by isothermal titration calorimetry in cholamine buffer at pH 7.0. The standard enthalpy change was determined to be -10.0 +/- 1.4 kcal/mol. Each calorimetric trace reveals an initial exothermic phase followed by an endothermic phase. The calorimetric data could be fit to a kinetic model involving a bimolecular combination of copper(II) and apoazurin in an exothermic process (k = 2 +/-1 x 103 M-1 s-1, DeltaH degrees = -19 +/- 3 kcal/mol) to form an intermediate that spontaneously converts to Cu(II)-azurin in an endothermic process (k = 0.024 +/- 0.01 s-1, DeltaH degrees = +9 +/- 3 kcal/mol). These data suggest that copper(II) first combines with apoazurin in an irreversible process to form an intermediate that converts to copper(II)-azurin in a process driven by the release of water. The overall standard free energy of copper(II) binding to apoazurin is estimated to be -18.8 kcal/mol.
authors.affiliation: Department of Chemistry, Johns Hopkins University, 3400 Charles Street, Baltimore, Maryland 21218, USA.
authors.forename: Cheryl A
authors.initials: CA
authors.lastname: Blasie
authors.forename: Jeremy M
authors.initials: JM
authors.lastname: Berg
mesh_terms: D001059:Apoproteins / Q000737:chemistry* / Q000378:metabolism; D001400:Azurin / Q000737:chemistry* / Q000378:metabolism; D002151:Calorimetry; D003300:Copper / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D011485:Protein Binding; D013816:Thermodynamics
chemical_list: D001059:Apoproteins; C038778:apoazurin; D001400:Azurin; D003300:Copper