title: Thermodynamics of the alkaline transition in phytocyanins.
abstract: The thermodynamics of the alkaline transition which influences the spectral and redox properties of the type 1 copper center in phytocyanins has been determined spectroscopically. The proteins investigated include Rhus vernicifera stellacyanin, cucumber basic protein and its Met89Gln variant, and umecyanin, the stellacyanin from horseradish roots, along with its Gln95Met variant. The changes in reaction enthalpy and entropy within the protein series show partial compensatory behavior. Thus, the reaction free energy change (hence the pK (a) value) is rather variable. This indicates that species-dependent differences in reaction thermodynamics, although containing an important contribution from changes in the hydrogen-bonding network of water molecules in the hydration sphere of the protein (which feature enthalpy-entropy compensation), are to a large extent protein-based. The data for axial ligand variants are consistent with the hypothesis of a copper-binding His as the deprotonating residue responsible for this transition.
authors.affiliation: Department of Chemistry, University of Modena and Reggio Emilia, Via Campi 183, 41100 Modena, Italy.
authors.forename: Gianantonio
authors.initials: G
authors.lastname: Battistuzzi
authors.forename: Marzia
authors.initials: M
authors.lastname: Bellei
authors.forename: Christopher
authors.initials: C
authors.lastname: Dennison
authors.forename: Giulia
authors.initials: G
authors.lastname: Di Rocco
authors.forename: Katsuko
authors.initials: K
authors.lastname: Sato
authors.forename: Marco
authors.initials: M
authors.lastname: Sola
authors.forename: Sachiko
authors.initials: S
authors.lastname: Yanagisawa
mesh_terms: D003300:Copper / Q000737:chemistry*; D014644:Genetic Variation; D006639:Histidine; D006860:Hydrogen Bonding; D008667:Metalloproteins / Q000737:chemistry* / Q000235:genetics; D010084:Oxidation-Reduction; D044367:Phase Transition; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics; D013057:Spectrum Analysis; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D008667:Metalloproteins; D010940:Plant Proteins; C002054:umecyanin; D014867:Water; C003343:stellacyanin protein, plant; D006639:Histidine; D003300:Copper