Derivation of the thermodynamic parameters involved in the elucidation of protein thermal profiles

Figure 3 (A) fo as a function of urea concentration. The arrows indicate the points that were used for calculating Ko and AGo. (B) Plot of AGo versus urea molarity for calculation of AGo(H20) References i Robinson, C Vet al (1994) Nature 372,646-651 2Anfinsen, C B (1973) Science 181,223-230 3Creighton, T E (1990) Biochem J 270, 1-16 4Lowry, O H, Rosebrough, N J, Farr, A L and Randall, R J (1951) J Biol Chem 193, 265-275 5Edward, F B , Rombauer, R B and Campbell, B J (1969) Biochim Biophys Acta 194, 234-245 6Tanford, C (1968) Adv Prot Chern 3, 121-282 7pace, C N (1975) Crit Rev Biochem 3, 1-43 8Pace, C N (1986) Methods Enzymol 131,266-280 0307-4412(95)00049-6 Derivation of the Thermodynamic Parameters Involved in the Elucidation of Protein Thermal Profiles A A SABOURY and A A MOOSAVI-MOVAHEDI* Institute of Biochemistry and Biophysics* University of Tehran and Department of Chemistry Terbiat-Modares University Tehran, Iran Introduction Globular proteins are large molecules. They contain typically 102-103 amino-acid residues ie 103-104 atoms. The total covalent bond energy is hence of the order of 105 joules per mole. In dramatic contrast, the forces which determine the three- dimensional structure are small. The total energy involved in the folding process for an entire protein molecule is comparable with that involved in one single covalent bond. Furthermore, this represents the resultant of a large number of different kinds of weak interactions, both intra-molecular and between the protein and the surrounding solvent. [This is not unrelated to the difficulties involved in predicting the secondary and tertiary structure from the primary sequence]. The equilibrium state of the native folded protein must therefore be regarded as representing a delicate balance between a large number of weak interactions each of which is sensitive to temperature and the state of the surrounding solvent (ie pH, ionic strength, presence of hydrogen bond breaking solutes such as urea, presence of amphiphilic compounds which affect the balance of hydrophobic and hydrophilic interactions.) Disruption of the tertiary structure to the extent that there is loss of biochemical activity is known as denaturation. Clearly on the basis of what has been said above this may involve very minor energy changes. The main purpose of denaturation studies has always been to provide additional information on the structure, properties, and function of proteins. 1-3 Denaturation can be brought about in many ways. These include thermal denaturation (by raising the temperature), 4'5 chemical denatur- ation (by urea or ~guanidinum chloride)'