FVa degradation of recombinant APC variants in the presence of protein S.

To investigate the influence of protein S on the efficiency of the various APC variants in an FVa-degradation system, FVa (0.8 nM) from normal (A) or FV Leiden (B) plasma was incubated at 37°C for 10 minutes with increasing concentrations of the various APC variants in the presence or absence of protein S (100 nM). The remaining FVa activity was measured with the PTase assay as described in “Materials and methods.” WT APC, (○); WT APC, with human protein S (●); QGNSEDY-APC, (▵); QGNSEDY-APC with human protein S, (▴); Note the logarithmic y-axes. Each point is the mean of 2 independent experiments performed in duplicate, and the error bars represent the standard deviation.