The importance of protein structure and conformation in the preparation of phospholipase-free cardiotoxin from snake venom.

Hydrophobic interactions of cobra venom phospholipase A2 (Mr 13 400) in saline with Sephadex gels and its stability towards denaturation in 6 M guanidine-hydrochloride precluded the use of these solvents to remove traces (approx. 0.2%, w/w) of phospholipase A2 from cardiotoxin (Mr 6800) by gel chromatography. Phospholipase-free (less than 0.001%, w/w) cardiotoxin could, however, be obtained by gel chromatography in 8 M urea or 80 mM phenylalanine. Stokes radius and circular dichroism measurements showed that the hydrophobic retardation of phospholipase A2 was abolished but that the hydrodynamic size and conformation of neither protein was affected, thereby facilitating separation.