화학공학소재연구정보센터
Thermochimica Acta, Vol.291, No.1-2, 141-153, 1997
Prediction and Structural-Analysis of the Enthalpy of Ionization of Proteins
A theoretical model is proposed for the prediction and analysis of the acid-base calorimetric titration of proteins. The model is based on the inclusion of the additive calorimetric contributions in a semi-empirical electrostatic method. Any electrostatic approach predicting pK(a) values can be used for the analysis of calorimetric titration curves. The first step in the treatment is to find relationships between the ionization enthalpies of titratable amino acid residues and the relative solvent accessibilities of their ionizing atoms (AA(i)). This is achieved on the basis of relations between the experimental values of enthalpies of the ionization of appropriate model compounds in aqueous organic solutions and their dielectric permeabilities. The predicted calorimetric titration curves of myoglobin, cytochrome c, ribonuclease A, lysozyme and alpha-chymotrypsin are compared with the available experimental data. Our results describe qualitatively the calorimetric titration of the first four proteins, while assuming a possible artifact in an experimental lysozyme calorimetric titration and predict the titration curve of alpha-chymotrypsin. This paper also presents the development of an analysis of the differential calorimetric titration curves, which can describe the contributions of individual ionizable groups. Such an analysis is demonstrated for the case of ferri- or ferro-cytochrome c as an example.