Purification and characterization of a coagulant enzyme, okinaxobin II, from Trimeresurs okinavensis (himehabu snake) venom which releases fibrinopeptides A and B

A coagulant enzyme, okinaxobin I, which was purified from Trimeresurus okinavensis (himehabu snake) venom, releases specifically fibrinopeptide B from fibrinogen to form fibrin clots. In the present study, its isozyme denoted as okinaxobin II has been purified to homogeneity from the same venom by chromatographies on Sephadex G-100, CM-Toyopearl 650M, and FPLC Mono-Q columns. Differently from okinaxobin I, okinaxobin II specifically cleaved fibrinopeptides A and B from fibrinogen similarly as found for α-thrombin. The enzyme acted on fibrinogen with specific activity of 42 NIH units/mg at optimum pH of 8.0. Okinaxobin II was a monomeric glycoprotein with a mol. wt of 37,500 on SDS-PAGE, which was reduced to 29,500 after treatment with N-glycanase. Okinaxobin II was much more basic (pI=8.1) than okinaxobin I (pI=5.4). The N-terminal sequence was highly similar to those of okinazobin I and some other snake venom coagulant enzymes such as flavoxobin (Trimeresurus flavoviridis), batroxobin (Bothrops atrox and Bothrops moojeni), and catroxobin (Crotalus atrox). Okinaxobin II hydrolyzed tosyl-L-arginine methly ester and benzoyl-L-arginine p-nitroanilide. The esterase activity was strongly inhibited by diisopropylfluorophosphate and to a lesser extent by tosyl-L-lysine chloromethly ketone, indicating that the enzyme is a serine protease like α-thrombin. In terms of amino acid composition, okinaxobin II was similar to okinaxobin I and dissimilar to α-thrombin.