Volumetric characterization of alpha-chymotrypsinogen A in aqueous urea and alkylurea solutions at 25 degrees C

The apparent specific volume, phi(2), of alpha-chymotrypsinogen A (alpha-ct g 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 phi(2) on protein concentration was observed its val ues were equated with the corresponding specific volumes at the infinite di lution, (v) over bar(2)(0). The small positive changes in (v) over bar(2)(0 ) observed in urea and methylurea solutions at the highest denaturant conce ntration were ascribed to the complete unfolding of alpha-ctg A while signi ficantly larger positive changes observed in N, N'-dimethylurea and ethylur ea solutions were explained in terms of the incomplete unfolding of alpha-c tg A into a compact intermediate state.