title: New thermodynamic studies on ribonuclease A at low pH.
abstract: The Planck-Benzinger thermal work function, delta W zero(T), represents the heat-flux term which is responsible for breaking or forming the noncovalent bonds in macro-molecular interactions, while the temperature-invariant chemical bond energy, delta H zero(T zero), gives molecules the cohesiveness to form macromolecular structures. A method is described for evaluating delta H zero(T zero) at different temperatures for ribonuclease A at low pH in the standard state, in order to determine the effect of pH on the thermodynamic stability of this protein. Ribonuclease A at pH 1.13 has a delta H zero(T zero) value of 58 kcal mol-1; at pH 2.50, delta H zero(T zero) is 58, at pH 2.77, 59, and at pH 3.15, 60 kcal mol-1. In the conformational thermal transition of ribonuclease A at pH 2.8, the compensatory temperature ranges from 50 to 320 K, and delta H zero(T zero) is approximately 5-6 kcal mol-1. This widening temperature range is typical of the unfolding process. Such differences in the magnitude of the temperature-invariant chemical bond energy can be attributed to specific changes in the solvent ordering in the immediate domain of ribonuclease A.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Florida, College of Medicine, Gainesville 32610, USA.
authors.forename: P W
authors.initials: PW
authors.lastname: Chun
mesh_terms: D004795:Enzyme Stability; D006863:Hydrogen-Ion Concentration; D012259:Ribonuclease, Pancreatic / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D012259:Ribonuclease, Pancreatic