Binding of ¹²⁵I-FXII and¹²⁵I-rFXII-▵19 to kaolin and inhibition by unlabeled proteins. A volume of 50 μL of fivefold dilutions of nonlabeled proteins in PBS 0.1 % (wt/vol) Tween-20 (PT) was added to 50 μL of¹²⁵I-rFXII-▵19 (A) or ¹²⁵I-FXII (B) (0.025 pmol/mL) and then incubated with 50 μL of kaolin (0.032 mg/mL in PT) for 10 minutes at room temperature. The tubes were centrifuged for 2 minutes at 10,000g and the pellets were counted for radioactivity. Binding was expressed as the percentage of the total counts added and are the means ± standard error (SE) of two independent experiments in duplicate. Symbols: FXII (•), rFXII-▵19 (▴).