Fig. 4.
Enhancement of APC-dependent factor Va inactivation by wild-type protein S and variants.
A range of recombinant protein S concentrations (0 to 20 nM) was incubated with 0.1 nM APC, 3 nM factor Va, and 25 μM phospholipid vesicles for 2 minutes at 37°C. Remaining factor Va activity was then quantified using a prothrombinase assay, assessing thrombin generation with the chromogenic substrate S2238 (see text). Results are expressed relative to the remaining activity, with no protein S present (100%), as mean of 3 experiments ± SD. ♦ indicates commercial plasma purified human protein S; ▪, wild-type recombinant protein S; ●, protein S with Gly11Asp; ▴, protein S with Thr37Met; ⋄, dialyzed conditioned medium from cells transfected with the vector pcDNA6 diluted to the same extent as that for 20 nM wild-type protein S; ▵, 20 nM wild-type recombinant protein S added in the absence of APC.