21. Which description is NOT correct? (A) Allosteric interactions in Aspartate transcarbamoylase (ATCase) are mediated by large changes in quaternary structure. (B) Chymotrypsinogen is activated by specific cleavage of a single peptide bond. (C) Blood clotting is accomplished by a series of zymogens activation. (D) Glycosylation is a highly effective means of regulating the activities of target proteins.