FXIII activity measured with an incorporation assay. Upon FXIII activation with thrombin and Ca²⁺, TG activity was measured for up to 40 minutes. (A) FXIII activity of the wild-type and variants that were expressed to a measurable extent (ie, Arg100Gln, Arg100Leu, Glu111Leu, Asn112Val) is shown as absorbance over time (mean OD values ± standard deviation). The values are from 3 separate experiments. (B) The slopes of the activity curves during the first 10 minutes (red bars) and 20 minutes (blue bars) were calculated as change of optical density per minute (ΔOD/min). Data are depicted as mean ± standard deviation. The asterisk indicates statistical significance (P < .001).