Phospholipid micelles, but not vesicles, neutralize heparin: an explanation for the minimal effect of heparin on the prothrombin time

Although heparin acts as an anticoagulant by catalyzing the inactivation of thrombin (Ha) and factor Xa (Xa) by antithrombin (AT), heparin has little effect on the prothrombin time (FT). To explore this phenomenon, we examined the effect of several commercial thromboplastin reagents that do not contain heparin neutralizing agents on the heparincatalyzed second-order rate constants for lia and Xa inactivation by AT. The thromboplastin reagents, …