Resolution of isoforms of mutalysin II, the metalloproteinase from bushmaster snake venom

Mutalysin II, a zinc endopeptidase possessing direct-acting fibrinolytic activity has been previously purified from bushmaster (Lachesis muta muta) snake venom. We now report a method to isolate two isoforms of natural mutalysin II (mut IIa and mut IIb) using chromatographies on Sephacryl S-200, CM Sepharose CL 6B and Sephadex G-50. The two proteins are monomeric non-glycosylated proteinases with similar molecular masses of 23 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Tryptic peptide mapping of the two native enzymes suggested a large degree of structural similarity. Both isoforms showed high similarity in all enzymatic properties using fibrinogen, fibrin and dimethylcasein as substrates. Thus, the specific fibrinolytic activity was estimated as 12±1.04 and 11.5±1.02 U/μg for mut IIa and mut IIb, respectively. The antigenic cross-reactivity of both isoforms was examined using rabbit hyperimmune serum or immunoglobulin G anti-mut IIa assays on immunodiffusion microscope slides, indirect enzyme-linked immunoabsorbent assay and western blots. From these experiments it was concluded that the two metalloproteinases mut IIa and mut IIb share identical antigenic structures. Since the stability of mutalysin II is dependent upon the presence of zinc, we examined the EDTA sensitivity of the isoforms of mutalysin II. Thus, the IC₅₀ values (concentration of EDTA to produce 50% inhibition of dimethylcasein hydrolysis) for mut IIa is 180 μM and 165 μM for mut IIb.