Effects of annexin V on the activity of the anticoagulant proteins C and S.

The effects of annexin V on the anticoagulant activity of activated protein C (APC) and protein S were examined. Although annexin V did not influence the amidolytic potential of APC, it inhibited both APC and protein S function in a factor Va inactivation assay. Competition experiments demonstrated that annexin V inhibits protein S binding to phospholipid vesicles in a dose-dependent manner. These results demonstrate that annexin V effectively interferes with the anticoagulant arm of the hemostatic system.