APC-cofactor activity of protein S Heerlen in plasma-based assays.

(A) Protein S–dependent prolongation of the clotting time in an APTT-based assay. Wild-type protein S and protein S Heerlen were added at increasing concentrations to protein S–depleted plasma in the presence of APC, and the clotting times were recorded by the APTT-based assay. The concentrations of protein S refer to the final concentrations in the assay. The means ± SEM of 3 independent experiments performed in duplicate are shown. (B) Protein S–dependent prolongation of clotting time in the tissue-factor pathway. Wild-type protein S or protein S Heerlen were added to protein S–depleted plasma (final concentrations in the assay of between 0 and 100 nmol/L), and the APC-cofactor activities were measured after initiation of clotting by thromboplastin (TP) reagent diluted 1:10 and 1:100. The means of 2 independent experiments performed in duplicate are shown.