Purification and characterization of phosphodiesterase (exonuclease) from Cerastes cerastes (Egyptian sand viper) venom

A venom exonuclease 'phosphodiesterase' (E.C. 3.1.4.1) has been purified from Cerastes cerastes venom by a combination of gel filtration on Sephadex G-100 superfine and ion exchange chromatography on DEAE-Sepharose. The enzyme showed a single band on PAGE and SDS-PAGE and had a molecular weight of 110,000. The final preparation was purified 28 fold. It had no carbohydrate and it did not have protease or 5'-nucleotidase activities. Optimum temperature for enzyme activity was 56 degrees C. The enzyme was rapidly inactivated when pre-incubated above 40 degrees C. Energy of activation (Ea) was calculated to be 0.913. The optimum pH was 9.0. Cysteine, glutathione, dithiothreitol, 2-mercaptoethanol, ADP and AMP inhibited the enzyme. Cysteine caused a non-competitive inhibition, while ADP showed a competitive inhibition. EDTA at a concentration of 0.5 mM caused complete inhibition of the enzyme, which could be reversed by the addition of Ca2+ or Mn2+.