Kinetic Characterization of Leucurobin, a Coagulant Thrombin-Like Enzyme from the Venom of Bothrops leucurus

In the present study, the kinetic characterization of leucurobin, a thrombin-like enzyme isolated from the venom of Bothrops leucurus was evaluated. This serpent is very common in the northeast of Brazil, but little is known about its venom. Leucurobin showed amidase activity against chromogenic substrates of the peptidyl-pNA type containing an Arg residue at P1. D-Phe-Pro-Arg-pNA was observed to be the best substrate of those tested. The amidase activity of leucurobin with this substrate was strongly inhibited by sodium and potassium ions and was weakly inhibited by calcium and magnesium ions. Leucurobin presented a high coagulating activity in vitro with citrated human plasma and with purified bovine fibrinogen. The coagulating activity with fibrinogen was inhibited by the presence of sodium and potassium ions, but not by calcium or magnesium ions. No interference in the amidase and coagulating activities by the glycoside fraction of native leucurobin was observed. The S1 site was found to be anionic, and the S2 and S3 sites are hydrophobic.