Thermodynamics of the alkaline transition in phytocyanins |
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Authors: | Gianantonio Battistuzzi Marzia Bellei Christopher Dennison Giulia Di Rocco Katsuko Sato Marco Sola Sachiko Yanagisawa |
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Institution: | (1) Department of Chemistry, University of Modena and Reggio Emilia, Via Campi 183, 41100 Modena, Italy;(2) Institute for Cell and Molecular Biosciences, Medical School, Newcastle University, NE2 4HH Newcastle, UK |
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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. |
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Keywords: | Alkaline transition Thermodynamics Electron transfer Phytocyanins Cupredoxins |
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