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Kinetics and thermodynamics of thermal denaturation in acyl carrier protein
Author(s) -
Horvath L.A.,
Sturtevant J.M.,
Prestegard J.H.
Publication year - 1994
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.5560030113
Subject(s) - divalent , chemistry , denaturation (fissile materials) , ionic strength , differential scanning calorimetry , enthalpy , calorimetry , ionic bonding , crystallography , kinetics , inorganic chemistry , ion , aqueous solution , thermodynamics , organic chemistry , nuclear chemistry , physics , quantum mechanics
The denaturation of Escherichia coli acyl carrier protein (ACP) in buffers containing both monovalent and divalent cations was followed by variable‐temperature NMR and differential scanning calorimetry. Both high concentrations of monovalent salts (Na + ) and moderate concentrations of divalent salts (Ca 2+ ) raise the denaturation temperature, but calorimetry indicates that a significant increase in the enthalpy of denaturation is obtained only with the addition of a divalent salt. NMR experiments in both low ionic strength monovalent buffers and low ionic strength monovalent buffers containing calcium ions show exchange between native and denatured forms to be slow on the NMR time scale. However, in high ionic strength monovalent buffers, where the temperature of denaturation is elevated as it is in the presence of Ca 2+ , the transition is fast on the NMR time scale. These results suggest that monovalent and divalent cations may act to stabilize ACP in different ways. Monovalent ions may nonspecifically balance the intrinsic negative charge of this protein in a way that is similar for native, denatured, and intermediate forms. Divalent cations provide stability by binding to specific sites present only in the native state.