Purification, sequencing and characterization of pseudexin phospholipases A2 from Pseudechis porphyriacus (Australian red-bellied black snake).

Pseudexin is the name given to a mixture of toxic phospholipase A2 isoenzymes isolated from the venom of the Australian red-bellied black snake, Pseudechis porphyriacus. We found that this mixture consists of three components: pseudexins A, B and C, which we individually purified by reverse phase chromatography or by hydrophobic interaction chromatography. Pseudexins A and B had relatively low specific toxicities in mice (i.p. LD50 of 1300 and 750 micrograms/kg, respectively), while C was non-toxic. All three had similar phospholipase A2 activities (43-53 muequiv H+ released/min/mg protein). The complete amino acid sequences of pseudexins A and B were determined. Amino acids were identical at 91 of the 117 residues. The first 28 residues of pseudexin C were determined, sufficient to show that C is structurally similar to A and B, but not identical with either. As judged by reactions with antisera against several other snake phospholipase A2 toxins, pseudexins A, B and C have very similar antigenic structures. We noted extensive homology with other phospholipases.