Stabilization versus inhibition of TAFIa by competitive inhibitors in vitro
article
Two competitive inhibitors of TAFIa (activated thrombin-activable fibrinolysis inhibitor), 2-guanidinoethyl-mercaptosuccinic acid and potato tuber carboxypeptidase inhibitor, variably affect fibrinolysis of clotted human plasma. Depending on their concentration, the inhibitors shortened, prolonged, or had no effect on lysis in vitro. The inhibitor-induced effects were both tissue-type plasminogen activator (tPA) and TAFIa concentration-dependent. Inhibitor-dependent prolongation was favored at lower tPA concentrations. The magnitude of the prolongation increased with TAFIa concentration, and the maximal prolongation observed at each TAFIa concentration increased saturably with respect to TAFIa. A theoretical maximal prolongation of 20-fold was derived from a plot of the maximum prolongation versus TAFIa. This represents, for the first time, a measurement of the maximal antifibrinolytic potential of TAFIa in vitro. Because TAFIa spontaneously decays, the stabilization of TAFIa was investigated as a mechanism explaining the inhibitor-dependent prolongation of lysis. Both inhibitors stabilized TAFIa in a concentration-dependent, non-saturable manner. Although their KI values differed by three orders of magnitude, TAFIa was identically stabilized when the fraction of inhibitor-bound TAFIa was the same. The data fit a model whereby only free TAFIa decays. Therefore, the variable effects of competitive inhibitors of TAFIa on fibrinolysis can be rationalized in terms of free TAFIa and lysis time relative to the half-life of TAFIa.
Topics
Biomedical ResearchChemical activationTissueCompetitive inhibitorsBiochemistry2 guanidinoethylmercaptosuccinic acidPotato tuber carboxypeptidase inhibitorThrombin activatable fibrinolysis inhibitorTissue plasminogen activatorUnclassified drug3 (2 guanidinoethyl) 2 mercaptosuccinic acidCarboxypeptidaseCarboxypeptidase inhibitor, plantSuccinic acid derivativeVegetable proteinBlood clottingCompetitive inhibitionConcentration responseEnzyme kineticsEnzyme stabilityHalf life timeIn vitro studyPotatoProtein stabilityBinding competitionChemistryDose responseDrug antagonismMetabolismTheoretical modelSolanum tuberosumBinding, CompetitiveCarboxypeptidase UCarboxypeptidasesDose-Response Relationship, DrugEnzyme InhibitorsFibrinolysisHumansKineticsModels, TheoreticalPlant ProteinsProtein BindingSuccinatesTemperatureTime FactorsTissue Plasminogen Activator
TNO Identifier
237005
ISSN
00219258
Source
Journal of Biological Chemistry, 278(11), pp. 8913-8921.
Pages
8913-8921