VOLUMETRIC CHARACTERIZATION OF a-CHYMOTRYPSINOGEN A IN AQUEOUS UREA AND ALKYLUREA SOLUTIONS AT 25 °C†

Abstract: The apparent specific volume, j2, of a-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 j2 on protein concentration was observed its values were equated with the corresponding specific volumes at the infinite dilution, v 20. The small positive changes in v 20 observed in urea and methylurea solutions at the highest denaturant concentration were ascribed to the complete unfolding of a-ctg A while significantly larger positive changes observed in N,N’-dimethylurea and ethylurea solutions were explained in terms of the incomplete unfolding of a-ctg A into a compact intermediate state