Proenterokinase

Proenterokinase is the inactive precursor form of enterokinase, also known as enteropeptidase. Enterokinase is a serine protease that plays a crucial role in the digestive system. It is primarily produced by duodenal enterocytes, the cells lining the small intestine. The main function of enterokinase is to activate pancreatic zymogens, which are inactive enzyme precursors secreted by the pancreas. Specifically, it converts trypsinogen into its active form, trypsin. Trypsin then acts as a key enzyme in the digestive cascade, activating other pancreatic zymogens such as chymotrypsinogen, procarboxypeptidase, and proelastase. This cascade is essential for the efficient digestion of proteins in the small intestine.

The synthesis of proenterokinase occurs in the endoplasmic reticulum and Golgi apparatus of duodenal cells. It is then stored in secretory granules before being released into the intestinal lumen. The activation of proenterokinase to its active form, enterokinase, is an autocatalytic process. A small amount of active enterokinase can cleave proenterokinase at a specific site, leading to the release of an inhibitory peptide and the formation of the mature, active enzyme. This autocatalytic activation ensures a rapid and efficient initiation of the digestive enzyme cascade once sufficient proenterokinase is secreted. Genetic deficiencies in enterokinase can lead to protein maldigestion and malabsorption, resulting in severe gastrointestinal symptoms and failure to thrive in infants.