Effect on platelet FXIII and partial characterization of Lonomin V, a proteolytic enzyme from Lonomia achelous caterpillars

Contact with Lonomia achelous caterpillars venom induces a severe bleeding syndrome in humans. A constant finding in all reported cases is a marked de crease of blood coagulation factor XIII (FXIII), which has been attributed to the presence of a proteolytic enzyme, isolated and named Lonomin V, in t he hemolymph and hair secretion. In this study, the effect of Lonomin V on transglutaminase activity from human plasma, rabbit plasma, and platelet FX III was analyzed. The decrease of activity was more pronounced in platelet (A(2)) when compared with rabbit plasma (AB) and human plasma FXIII (A(2)B( 2)) This finding might be explained by the differences in FXIII molecular s tructure. In addition, platelet FXIII molecule was degraded by Lonomin to s everal fragments of low molecular mass. Lonomin V was stable over a wide ra nge of pH (6-8.5) and temperatures of -70 degrees C, -20 degrees C and betw een 4 to 24 degrees C, with a progressive decrease at 37 degrees C and tota l inactivation at 60 degrees C after 2 hours incubation. Diisopropyl fluoro -phosphate, phenylmethylsulfonyl fluoride, tosyl-l-lysine chloromethyl keto ne, and iodoacetamide abolished the effect of Lonomin V on FXIII; in contra st dithiothreitol and EDTA-Na enhance the activity. We concluded that Lonom in V is a serine proteinase with a free Cys essential for the enzymatic act ivity. Due to its proteolytic activity on FXIII, with concomitant impairmen t of fibrin cross-linking, Lonomin V might be useful in association with th rombolytic drugs for preventing rethrombosis. (C) 1999 Elsevier Science Ltd . All rights reserved.