Proteolytic cleavage sites. (A) Thrombin cleavage sites. Of the 3 thrombin cleavage sites, only 2 are present (Arg709 and Arg1545) in pseutarin C nonenzymatic subunit, but they are sufficient to release the activation peptide (B domain). (B) FXa cleavage sites. Although a similar site is found in pseutarin C nonenzymatic subunit, a proteolytic cleavage was observed at Arg346 (dotted arrow) in native pseutarin C. The additional FXa cleavage site on the light chain (Arg1765) is absent in pseutarin C. Numbering of the amino acids is based on human FVa sequence. (C) APC cleavage sites. Two of the 3 APC cleavage sites are absent in pseutarin C. Arrows indicate the site of cleavage in bovine FV (see “Proteolytic regulator of cofactor activity”).