Premium
Electrostatic Effects on the Thermodynamics of Protonation of Reduced Plastocyanin
Author(s) -
Battistuzzi Gianantonio,
Borsari Marco,
Di Rocco Giulia,
Leonardi Alan,
Ranieri Antonio,
Sola Marco
Publication year - 2005
Publication title -
chembiochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.05
H-Index - 126
eISSN - 1439-7633
pISSN - 1439-4227
DOI - 10.1002/cbic.200400310
Subject(s) - plastocyanin , protonation , chemistry , enthalpy , thermodynamics , electrostatics , entropy (arrow of time) , molecule , chemical physics , computational chemistry , ion , organic chemistry , physics , biochemistry , photosystem i , chloroplast , gene
The L12E, L12K, Q88E, and Q88K variants of spinach plastocyanin have been electrochemically investigated. The effects of insertion of net charges near the metal site on the thermodynamics of protonation and detachment from the copper( I ) ion of the His87 ligand have been evaluated. The mutation‐induced changes in transition enthalpy cannot be explained by electrostatic considerations. The existence of enthalpy/entropy ( H/S ) compensation within the protein series indicates that solvent‐reorganization effects control the differences in transition thermodynamics. Once these compensating contributions are factorized out, the resulting modest differences in transition enthalpies turn out to be those that can be expected on purely electrostatic grounds. Therefore, this work shows that the acid transition in cupredoxins involves a reorganization of the H‐bonding network within the hydration sphere of the molecule in the proximity of the metal center that dominates the observed transition thermodynamics and masks the differences that are due to protein‐based effects.