Summary
From the saliva of the vampire bat Desmodus rotundus, we isolated an unknown anticoagulant protein which we have named draculin. Its molecular mass as determined by non-reduced SDS-PAGE is about 83 kDa. The reduced
polypeptide shows a slower migration. HPLC in a molecular sieve matrix yields a single,
symmetrical peak corresponding to 88.5 kDa. Isoelectric focusing shows an acidic protein
with pI = 4.1–4.2. Aminoacid analysis is compatible with a single chain polypeptide
of about 80 kDa. Cyanogen bromide cleavage yields a single 16-aminoacid peptide, corresponding
to the amino-terminus of the native molecule. Draculin inhibits the activated form
of coagulation factors IX and X. It does not act on thrombin, trypsin, chymotrypsin
and does not express fibrinolytic activity. The inhibition is immediate and not readily
reversible, with a stoichiometry of about two molecules of draculin per molecule of
factor IXa or Xa. Surprisingly, the inhibitory activity against either factor is not
affected by the presence of the other. Draculin binds quantitatively to either immobilised
factor Xa or factor IXa. Our preliminary interpretation is that there are two forms
of draculin that hardly differ in structure. Both bind to factor Xa and to factor
IXa but one form inhibits factor Xa and the other inhibits factor IXa.
When added to plasma, draculin increases the lag phase as well as the height of the
peak of thrombin generation.
