Canadian Medical Guide > Chemicals and Drugs > Enzymes and Coenzymes > Enzyme Precursors Terms and Definitions

Enzyme Precursors

Medical Definition:	Physiologically inactive substances that can be converted to active enzymes.
Guide Notes:	IM; coord with specific enzyme (IM); zymogen granules: index under ZYMOGEN GRANULES see SECRETORY VESICLES (IM) + ENZYME PRECURSORS (IM) + specific enzyme (IM)

Enzyme Precursors Categories.

	Chymotrypsinogen
	Complement Factor B - A glycine-rich, heat-labile beta-glycoprotein found in blood. It is a proactivator of complement 3 in the alternate pathway of complement activation. Factor B is converted by Factor D to COMPLEMENT 3 CONVERTASE. EC 3.4.21.47.
	Pepsinogens - Proenzymes secreted by chief cells, mucous neck cells, and pyloric gland cells, which are converted into pepsin in the presence of gastric acid or pepsin itself. (Dorland, 28th ed) In humans there are 2 related pepsinogen systems: PEPSINOGEN A (formerly pepsinogen I or pepsinogen) and PEPSINOGEN C (formerly pepsinogen II or progastricsin). Pepsinogen B is the name of a pepsinogen from pigs.
	Plasminogen - Precursor of fibrinolysin (plasmin). It is a single-chain beta-globulin of molecular weight 80-90,000 found mostly in association with fibrinogen in plasma; plasminogen activators change it to fibrinolysin. It is used in wound debriding and has been investigated as a thrombolytic agent.
	Protein C - A vitamin-K dependent zymogen present in the blood, which, upon activation by thrombin and thrombomodulin exerts anticoagulant properties by inactivating factors Va and VIIIa at the rate-limiting steps of thrombin formation.
	Prothrombin - A plasma protein that is the inactive precursor of thrombin. It is converted to thrombin by a prothrombin activator complex consisting of factor Xa, factor V, phospholipid, and calcium ions. Deficiency of prothrombin leads to hypoprothrombinemia.
	Trypsinogen - The inactive proenzyme of trypsin secreted by the pancreas, activated in the duodenum via cleavage by enteropeptidase. (Stedman, 25th ed)

Enzyme Precursors Medical Definitions and Terms

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