Summary
The three phospholipase A2 isoenzymes from Naja nigricollis crawshawii snake venom inhibit both blood coagulation and platelet aggregation. To investigate
the correlation between phospholipid splitting ability of these enzymes and their
inhibitory activities, the effects of various preincubation times and the inclusion
of EDTA were examined. Preincubation of plasma and thromboplastin with the phospholipase
isoenzymes resulted in an increase in Ca2+-initiated clotting time with time of preincubation. Incubation of the isoenzymes
with EDTA before their addition to the plasma-thromboplastin mixture reduced the anticoagulant
effect. These results indicate that the catalytic activity contributes at least partially
to the anticoagulant effect. However, inhibition of platelet aggregation appears to
be independent of enzymatic activity since there is no increase in inhibition with
time of preincubation of platelets and phospholipases, and inclusion of EDTA has no
significant effect on inhibition of aggregation. All three enzymes appear to belong
to class B of the platelet affector PLA2 enzymes as determined by platelet effects, since they do not initiate platelet aggregation.
Keywords
Anticoagulant - Phospholipase - Platelet aggregation -
Naja nigricollis
- Snake venom
