VOLUMETRIC CHARACTERIZATION OF a-CHYMOTRYPSINOGEN A IN AQUEOUS UREA AND ALKYLUREA SOLUTIONS AT 25 °C
Nataša Poklar, Romana Cerc-Korošec, Branko Èeh and Gorazd
Department of Chemistry, University of Ljubljana, Aškerèeva 5, 1000 Ljubljana, Slovenia
The apparent specific volume, phi2, of alpha-chymotrypsinogen A (a-ctg A) in a aqueous solutions containing different amount of urea, methylurea, N,N'-dimethylurea or ethylurea was determined from density measurements. Since no dependence of phi2 on protein concentration was observed its values were equated with the corresponding specific volumes at the infinite dilution v. The small positive changes in v observed in urea and methylurea solutions at the highest denaturant concentration were ascribed to the complete unfolding of alpha-ctg A while significantly larger positive changes observed in N,N'-dimethylurea and ethylurea solutions were explained in terms of the incomplete unfolding of alpha-ctg A into a compact intermediate state.