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

A coagulant enzyme, okinaxobin I, which was purified from Trimeresurus okinavenis (himehabu snake) venom, released 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 alpha-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 okinaxobin 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 methyl ester and benzoyl-L-arginine p-nitroanilide. The esterase activity was strongly inhibited by diisopropylfluorophosphate and to a lesser extent by tosyl-L-lysine chloromethyl ketone, indicating that the enzyme is a serine protease like alpha-thrombin. In terms of amino acid composition, okinaxobin II was similar to okinaxobin I and dissimilar to alpha-thrombin.