Summary
Wheat germ agglutinin (WGA) and concanavalin A (Con-A) (also red kidney bean agglutinin,
PHA) have been found to be inhibitors of plasma clotting in vitro. At 40 µg/ml and
250 µg/ml (4.4 µM and 10 µM in carbohydrate binding sites, final concentrations) respectively,
WGA and Con-A are able to double the activated partial thromboplastin time of normal
human control plasma. Their inhibitory effect is due to their capacity to interact
with the carbohydrate portion of blood clotting factors. It is totally abolished in
the presence of specific saccharides for WGA or Con-A and is attenuated in the presence
of 4% (v/v, final concentration) of human erythrocytes. The action of WGA is mediated
by its ability to interact with N-acetylneuraminic acid. When purified phospholipid
vesicles plus kaolin are used as an activator instead of cephalidin, this effect persists
to the same extent. These two lectins also prolong the plasma clotting time using
Russell's viper venom plus purified phospholipid vesicles as an activator. Quick's
time was also prolonged by WGA and Con-A but to a lesser extent in this case. WGA
can interact directly with some purified blood clotting factors (IX, X and II) in
a classical lectin-glycoprotein precipitin reaction. When assessed at individual factors
level in whole plasma using clotting assays, direct inhibitions by WGA are only apparent.
Keywords
Plasma coagulation - Reversible inhibition - Lectins
