Serine proteases are enzymes that belong to a subfamily of peptidases (cleaved proteins and peptides). In the active centre of the serine proteases (this also applies to some other enzymes), 3 amino acids, aspartic acid, histidine and, in essential function, serine (name-giving), are arranged in a special formation. This formation is called the catalytic triad. In this special formation the cleavage of a substrate can take place in peptidases.
Serine peptidases include the digestive enzymes trypsin, chymotrypsin, elastase, plasmin and thrombin. A specific inhibition of serine proteases is achieved by serpines. Many enzymes of the coagulation system are serine proteases and serine protease inhibitors.