Purification and biochemical characterization of atroxase, a nonhemorrhagic fibrinolytic protease from western diamondback rattlesnake venom

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Abstract
Crotalus atrox venom contains a variety of proteases which render fibrinogen incoagulable and solubilize fibrin. One of these proteases was purified by using ion-exchange and gel permeation liquid chromatography. The protease, called atroxase, consists of a single nonglycosylated polypeptide chain with a molecular weight of 23 500 and an isoelectric point of pH 9.6. Amino acid analysis indicates atroxase to contain 206 residues with no sulfhydryl groups. Metal analysis found zinc and potassium at 1 mol/mol of protein, and calcium at 0.3 mol/mol of protein. Proteolytic activity is inhibited by ethylenediaminetetraacetate and .alpha.2-macroglobulin. Maximal proteolytic activity occurs at pH 9.0 and 55.degree. C. Proteolytic specificity, using oxidized insulin B chain, is similar to that of several hemorrhagic toxins found within the same venom, yet atroxase shows no hemorrhagic activity and exhibits low lethality when tested on Swiss Webster mice. Atroxase, an A.alpha., B.beta. fibrinogenase, cleaves the A.alpha. chain of fibrinogen first followed by the B.beta. chain and shows no effect on the .gamma. chain. The nonspecific action of the enzyme results in the extensive hydrolysis of fibrogen which releases a variety of fibrinopeptides. Fibrin solubilization appears to occur primarily from the hydrolysis of .alpha.-polymer and unpolymerized .alpha. and .beta. chains. Although crude venom induces platelet aggregation, atroxase demonstrated no ability to induce or inhibit aggregation.