Proenzimet

Proenzimet, commonly referred to as proenzymes or zymogens, are inactive precursor forms of enzymes. They are produced with an activation segment that blocks the active site, keeping the enzyme inactive until the appropriate signal for activation is received. This arrangement helps prevent unintended proteolysis within the cells that synthesize the enzyme.

Activation typically occurs through proteolytic cleavage of the activation peptide. This cleavage can be performed by another protease or triggered by changes in the local environment, such as pH shifts. After the propeptide is removed or altered, the enzyme folds into its active form and can catalyze its specific chemical reaction. Activation can occur in a single step or through a cascade of processing events.

Many well-known enzymes are produced as proenzymes. In digestion, pepsinogen is secreted by gastric cells and becomes pepsin in the acidic stomach. In the small intestine, trypsinogen and chymotrypsinogen are activated to trypsin and chymotrypsin, starting a proteolytic cascade that digests proteins. In blood coagulation, prothrombin is activated to thrombin, a key step in the coagulation process. Other examples include procarboxypeptidases and proelastase, which are converted to their active forms in appropriate compartments.

Proenzymes provide spatial and temporal control of proteolysis, ensuring enzymes act only where and when needed. They are typically stored in secretory granules or compartments to prevent autodigestion. Premature activation within tissues can lead to damage, as seen in pancreatitis, or contribute to bleeding disorders if activation is disrupted. The study of proenzymes is central to understanding digestion, coagulation, development, and several disease processes.