SkM and CM myosins exhibit TF-like activity. Varying concentrations of myosin were mixed with 1 nM fVIIa and 150 nM fX for 5 min before quenching with EDTA. FXa generation was then measured using substrate S-2765. (A) SkM (1 µM, red circles) supported generation of fXa equivalent to 7.3 pM TF based on a control curve of relipidated human TF, wheras 1 µM CM myosin (blue open circles) supported generation of fXa equivalent to 320 pM TF. (B) TFPI was preincubated with either relipidated, recombinant human TF (7.3 pM, purple triangles), SkM (1 µM, red circles), or CM (23.7 nM, open circles) for 5 minutes. fVIIa and fX were then added, and fXa generation was assessed after 30 min. Control experiments lacking TF (green squares) were run by incubating 3 nM fXa and 1 nM fVIIa with TFPI for 30 min and then testing activity. TFPI over 2 nM inhibits fXa activity >50%. However, TFPI inhibits myosin-mediated fXa activation by an additional 76% (SkM) and 84% (CM) over its effect on fXa (inhibition of TF-mediated fXa activation is 87%). Data shown are mean ± SD for 3 (SkM) and 2 (CM) experiments, each performed in duplicate.