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

H. Y. Halim, E. A. Shaban, M. M. Hagag, E. W. Daoud and M. F. El-Asmar. Purification and characterization of phosphodiesterase (exonuclease) from Cerastes cerastes (Egyptian sand viper) venom. Toxicon 25, 1199 – 1207, 1987. — 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°C. The enzyme was rapidly inactivated when pre-incubated above 40°C. Energy of activation ( E a ) 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 Ca 2+ or Mn 2+.