proenzymen

Proenzymes, also known as zymogens, are inactive precursor enzymes that require a biochemical change, most commonly proteolytic cleavage, to become active enzymes. They are synthesized in various tissues and secreted in an inactive form to prevent unintended proteolysis of cellular components. Activation typically involves irreversible removal or modification of an inhibitory propeptide that blocks the active site, or conformational changes that reveal catalytic residues. Activation is often spatially or temporally regulated, occurring in a specific anatomical site or in response to a physiological trigger.

Many proenzymes play essential roles in digestion and hemostasis. Common examples include pepsinogen, which is converted to pepsin in the acidic environment of the stomach; trypsinogen and chymotrypsinogen, pancreatic zymogens activated in the small intestine (trypsinogen by enteropeptidase to trypsin, which then activates the other pancreatic zymogens); and procarboxypeptidases, which become carboxypeptidases A and B. In the bloodstream, several coagulation and fibrinolytic factors are produced as proenzymes, such as prothrombin (activated to thrombin) and plasminogen (activated to plasmin) as part of the coagulation and fibrinolytic cascades. Prohormones with enzymatic activity are sometimes included in discussions of proenzymes, though these are typically referred to as proenzymes in the context of enzyme maturation rather than hormone signaling.

Physiologically, the use of proenzymes prevents premature or widespread proteolysis, enabling controlled activation at the appropriate location and time. Dysregulation or mutations affecting zymogen activation can contribute to diseases such as pancreatitis or coagulation disorders.