Inhibition of factor XIa by ZPI.

Mixtures containing factor XIa (1 nmol/L), with or without high molecular weight kininogen (HK, 0.5 μmol/L), and with or without heparin (0.20 U/mL), were constructed in HSA at room temperature, and the reactions were initiated by the addition of ZPI (69 nmol/L). Remaining factor XIa activity was determined by amidolytic assay. ○, factor XIa alone; ■, factor XIa with HK; ▵, factor XIa with heparin.