Proteases (also known as peptidases or proteinases) are the 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. There are many important proteases which play key roles in many cell processes including proteasome, gamma-secretase, HCV protease, Aminopeptidase, and Procollagen C Proteinase.