Effect of factor X on the inactivation of factor VIIIa by human APC and protein S.

(A) Factor VIIIa activity was determined for reactions containing 200 nmol/L factor VIIIa alone (open diamonds), factor VIIIa plus 40 nmol/L APC (circles), and factor VIIIa plus APC plus 400 nmol/L factor X (squares). Open symbols were in the absence and closed symbols were in the presence of 250 nmol/L protein S. (B) Residual A1 subunit was determined for the above reactions run in the presence of APC (circles) and APC plus factor X (squares). Open and closed symbols represent the absence and presence of protein S, respectively. Curves were derived from scans of the Western blots obtained using the 58.12 anti-A1 subunit antibody. (C) Residual A2 subunit was determined for the above reactions run in the presence of APC (circles) and APC plus factor X (squares). Open and closed symbols represent the absence and presence of protein S, respectively. Curves were derived from scans of the Western blots obtained using the R8B12 anti-A2 subunit antibody. (D) Residual A1 subunit was determined after addition of 40 nmol/L APC to reactions containing 0 (circles), 200 (squares), 400 (triangles), and 800 nmol/L (diamonds) factor X.