In
contrast, the venom of V. russelli, a well-known factor X
activator, induced clotting in these conditions. Thus, the
coagulant activity of B. asper venom is due to prothrombin
activators and thrombin-like components.
When four MCD of venom were incubated with varying
concentrations of batimastat, a dose-dependent inhibition of
this effect on plasma was evident (Fig. 4); 20 mM batimastat
completely abrogated this effect, since no clotting of plasma
was observed even after 15 min of incubation. The MCD of
venom incubated with 100 mM batimastat was then
determined on plasma; MCD in these conditions was
50 mg (Fig. 5A), which corresponds to 100 times the
MCD of venom alone (0.5 mg). In order to determine the
role of serine proteinases in the coagulant activity of B. asper
venom, inhibition by PMSF was studied. As shown in
Fig. 5B, PMSF has little inhibitory effect on the clotting
activity of the venom. However, 4 mM PMSF completely
inhibited the clotting activity of B. asper venom on
fibrinogen (results not shown), since this activity depends
on thrombin-like serine proteinases. When both batimastat
and PMSF were incubated with the venom, coagulant
activity on plasma was completely abrogated, even when
using a venom dose of 50 mg, i.e. 100 times the MCD.
Batimastat, but not PMSF, completely inhibited the
prothrombin activating activity in B. asper venom (results
not shown