Enzymes are able to be activated by proteolysis, cleaving their structure to give the active form. This allows protease activity to be controlled, as seen in blood clotting cascades where certain proteins are only activated when certain conditions are met.
Chymotrypsinogen is an inactive form of chymotrypsin. To activate chymotrypsinogen, trypsin cleaves the protein into three sections, which then form disulfide bonds between to form the final, active chymotrypsin protein. The activity of trypsin can be modulated to control the activation of chymotrypsin, allowing the cell to control proteolysis.
Inhibitor proteins can be used to prevent or supress the activation of proteases, reducing the amount of proteolysis. This can be useful in certain pathologies, such as haemophilia, where certain pathways are overactive / inactive.