= Plasminogen
The <protein> <plasminogen> is the inactive precursor of <plasmin>, a <protease> that helps break down <fibrin> in a <blood clot>. Activation requires cleavage of a particular <peptide bond>, converting an abundant circulating precursor into an active <enzyme>. Production of the precursor and activation of that precursor are therefore separate control points. <NCBI Gene by the National Library of Medicine>[Human PLG, Gene ID 5340, Summary: zymogen, plasminogen activators and fibrin degradation]{ref}
A useful measurement distinction follows: a sample can contain substantial <plasminogen> yet have little ongoing <proteolysis>. An assay that supplies an activator tests potential activity under those assay conditions; it does not directly report the original rate of clot breakdown. Local activation and inhibition help confine <protease> action to appropriate sites.
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