Thrombin formation and thrombin substrates.

Early TAT complex formation from time 0 to 6 minutes is illustrated on a semilogarithmic scale along with thrombin generation calculated from the rate of FPA generation. The concentration of TAT required for the transition to rapid product formation for osteonectin (OSN, platelet activation), factor XIII activation (fXIIIa), FPA release, FPB release, and TAT propagation was calculated to be 0.51 ± 0.18 nM, 0.84 ± 0.28 nM, 1.3 ± 0.4 nM, 1.7 ± 0.5 nM, and 26 ± 6.2 nM, respectively. An extrapolation of the propagation phase for each substrate showed an initiation phase duration of 1.9 ± 0.2 minutes for platelet activation, 2.2 ± 0.6 minutes for factor XIII activation, 2.5 ± 0.7 minutes for FPA release, 2.8 ± 0.8 minutes for FPB release, and 4.6 ± 0.6 minutes for the onset of TAT propagation phase. The percent of TAT present at the point of activation is shown in parenthesis. Thrombin concentration calculated from the rate of FPA generation is shown as a dashed line.