Proteases (also known as peptidases or proteinases) are a subgroup of hydrolase enzymes that catalyze the cleavage of peptide bonds within proteins. There are two main subtypes of proteases: exoproteases, which hydrolyze peptide bonds at the terminus of polypeptide chains; and endoproteases, which act internally. Proteases are involved in a vast array of physiological processes, from simple digestion of food to complex signaling cascades such as the apoptotic caspase-activated cascade.