title: Notable Stabilization of α-Chymotrypsin by the Protic Ionic Additive, [ch][dhp]: Calorimetric Evidence for a Fine Enthalpy/Entropy Balance.
abstract: An impact of 0.5 to 3 M choline dihydrogen phosphate, [ch][dhp], the biotechnologically relevant ionic substance, on the thermal stability of a model globular protein, α-chymotrypsin (α-CT), has been studied exploiting the highly sensitive differential scanning calorimetry (DSC) technique. The notable overall stabilizing effect of 11 ± 2 K regarding the thermal transition (melting) temperature, T m , has been detected. For this kind of series, for the first time, the calorimetric melting enthalpy (ΔH cal) and transition entropy (ΔS m ) parameters have been determined simultaneously throughout. The first analysis indicated a two-phase impact implying (a) the initial, dramatic drop in both ΔH cal and ΔS m , obviously connected to specific, direct interaction between the [ch][dhp] components and α-CT's charged groups (within 0 to 1 mol/L [ch][dhp]), leading to the essential rearrangement of the interfacial hydrogen-bonded (HB) network; and (b) the follow-up (within 1 to 3.0 mol/L [ch][dhp]), modest changes in ΔH cal and lack of changes in ΔS m , seemingly connected with a subsequent steady strengthening of already reformed HB network, respectively. These changes, presumably, are primarily facilitated by Coulombic interactions between the [dhp] anions and solvent-exposed positively charged amino groups of α-CT.
authors.affiliation: Department of Biophysics, I. Beritashvili Center of Experimental Biomedicine, Gotua 14, 0160 Tbilisi, Georgia.
authors.forename: Sophio
authors.identifier: 0000-0002-8812-3712
authors.initials: S
authors.lastname: Uchaneishvili
authors.affiliation: Department of Biophysics, I. Beritashvili Center of Experimental Biomedicine, Gotua 14, 0160 Tbilisi, Georgia.
authors.forename: Maya
authors.initials: M
authors.lastname: Makharadze
authors.affiliation: Department of Biophysics, I. Beritashvili Center of Experimental Biomedicine, Gotua 14, 0160 Tbilisi, Georgia; Institute for Biophysics and Bionanosciences at the Department of Physics, I. Javakhishvili Tbilisi State University, I. Chavchavadze Avenue 3, 0128 Tbilisi, Georgia.
authors.forename: Mikhael
authors.identifier: 0000-0002-8984-3455
authors.initials: M
authors.lastname: Shushanyan
authors.affiliation: Department of Chemistry and Pharmacy, Friedrich-Alexander University of Erlangen-Nürnberg, Egerlandstraße 1, 91058 Erlangen, Germany.
authors.forename: Rudi
authors.initials: R
authors.lastname: van Eldik
authors.affiliation: Department of Biophysics, I. Beritashvili Center of Experimental Biomedicine, Gotua 14, 0160 Tbilisi, Georgia; Institute for Biophysics and Bionanosciences at the Department of Physics, I. Javakhishvili Tbilisi State University, I. Chavchavadze Avenue 3, 0128 Tbilisi, Georgia; Department of Chemistry and Pharmacy, Friedrich-Alexander University of Erlangen-Nürnberg, Egerlandstraße 1, 91058 Erlangen, Germany.
authors.forename: Dimitri E
authors.initials: DE
authors.lastname: Khoshtariya