Question

Please answer section a thru c:

11. Chymotrypsin is a protease, an enzyme that cleaves peptide bonds. a) At pH 2, the enthalpy and entropy of denaturation for chymotrypsin are +418 kJ/mol and +1.32 kJ/mol respectively. Calculate the melting temperature for chymotrypsin. b) Chymotrypsin inhibitor (CI) is a small protein that binds to chymotrypsin with high affinity and prevents protease activity. The dissociation constant for Chymo-CI is 110 PM in a salt free solution. What is the Gibbs free energy for binding at 37°C? c) Mutation of residue-80 which is an arginine in Cl reduces the binding affinity by a factor of 2. Predict the binding affinity of chymotrypsin and CI in a 1 M NaCl solution. Justify your answer.

Answer 1

a) The melting temperature for chymotrypsin = $\Delta$H/$\Delta$S = (418 kJ/mol)/(1.32 kJ/mol.K) = 316.67 K

b) $\Delta$G = -RT ln(K) = -8.314 J/mol.K * (37+273) K * ln(110*10^-12) = 59.1 kJ/mol