Thrombin
mammalian protein found in Homo sapiens
Thrombin (factor IIa, EC 3.4.21.5) is a serine protease that converts fibrinogen into strands of insoluble fibrin, as well as catalyzing many other coagulation-related reactions.
Prothrombin (coagulation factor II) is encoded in the human by the F2 gene. It is proteolytically cleaved during the clotting process by the prothrombinase enzyme complex to form thrombin.
History
After the description of fibrinogen and fibrin, Alexander Schmidt hypothesised the existence of an enzyme that converts fibrinogen into fibrin in 1872.
Prothrombin was discovered by Pekelharing in 1894.
Physiology
Synthesis
Thrombin is produced by the enzymatic cleavage of two sites on prothrombin by activated Factor X (Xa). The activity of factor Xa is greatly enhanced by binding to activated Factor V (Va), termed the prothrombinase complex. Prothrombin is produced in the liver and is co-translationally modified in a vitamin K-dependent reaction that converts 10-12 glutamic acids in the N terminus of the molecule to gamma-carboxyglutamic acid (Gla). In the presence of calcium, the Gla residues promote the binding of prothrombin to phospholipid bilayers. Deficiency of vitamin K or administration of the anticoagulant warfarin inhibits the production of gamma-carboxyglutamic acid residues, slowing the activation of the coagulation cascade.
“Thrombin” enters the record as mammalian protein found in Homo sapiens. Crown Archives preserves that source wording while asking what Thrombin, mammalian and protein can confirm, complicate or overturn.
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The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated Jan 26, 2026. The linked authority identifier is Q409166. The Library of Congress control number is sh85135066. 1 of 1 selected statements include explicit references; 1 carry qualifiers and 0 use preferred rank. The first chronological checks are 1872 and 1894.
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