INTERACTIONS OF ALPHA-CHYMOTRYPSINOGEN A WITH ALKYLUREAS

Solvation of alpha-chymotrypsinogen A (alpha-ctg A) in aqueous urea, m ethylurea, N,N'-dimethylurea and ethylurea was studied by density meas urements. From the densities at constant molality and at constant chem ical potential the preferential solvation parameters were determined. In urea and methylurea preferential solvation was observed, whereas in N,N'-dimethylurea and ethylurea at higher concentration water is pref erentially bound. From preferential solvation data Gibbs free energy o f transfer of alpha-ctg A from water to urea and alkylurea solutions w ere calculated. Since the enthalpies of transfer were determined previ ously, the entropies of transfer could also be obtained so that a comp lete thermodynamic description is available. An attempt is made to int erpret the values of the thermodynamic quantities in terms of various interactions involved in solvation as well as to calculate the exchang e constant by using the model of weak interactions. In solvation of al kylureas the hydrophobic nature of the alkyl groups is clearly reflect ed.