Some of the loops between the strands include helical sections. Recall that chymotrypsin consists of three chains, due to several cleavages of the initial zymogen polypeptide. These chains are joined by disulphide bonds. Trypsin on the other hand is a single chain, as the zymogen is activated by removal of the first six residues. Gail Schuman has produced this material on the trypsin zymogen, trypsinogen .
Proteases are all hydrolases - i.e. they cleave bonds by hydrolysis.
Although the serine proteases have no absolute specificity, they have strong preferences for the peptide bonds adjacent to specific amino acid residues. This specificity depends on the size and nature of the three residues which form the specificity pocket , described subsequently.