= Thrombin
<Thrombin> is a <protease> that converts soluble <fibrinogen> into <fibrin>, a principal structural component of a <blood clot>. It cleaves particular <peptide bonds> and releases short fibrinopeptides, enabling the remaining <fibrin> units to assemble. <Thrombin> is generated by activation of the precursor <prothrombin>.<Thrombin EC 3.4.21.5 in IUBMB Enzyme Nomenclature>[Reaction and Comments]{ref}
A simple clotting experiment makes the change visible: adding active <thrombin> to a suitable <fibrinogen> solution produces an assembling network. The resulting material is not a precipitate of the <enzyme> itself; a relatively small amount of catalyst can transform a much larger amount of its <substrate>. This separates the messenger-like activation step, the catalytic reaction and the mechanical structure of the final clot.
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