PURIFICATION AND CHARACTERIZATION OF PHOSPHODIESTERASE I FROM Walterinnesia aegyptia VENOM

A phosphodiesterase I (EC 3.1.4.1; PDE-I) was purified from Walterinnesia aegyptia venom by preparative native polyacrylamide gel electrophoresis (PAGE). A single protein band was observed in analytical native PAGE and sodium dodecyl sulfate (SDS)-PAGE. PDE-I was a single-chain glycoprotein with an estimated molecular mass of 158 kD (SDS-PAGE). The enzyme was free of 5′-nucleotidase and alkaline phosphatase activities. The optimum pH and temperature were 9.0 and 60°C, respectively. The energy of activation (Ea) was 96.4, the V_max and K_m were 1.14 µM/min/mg and 1.9 × 10^?3 M, respectively, and the K_cat and K_sp were 7 s^?1 and 60 M ^?1 min^?1 respectively. Cysteine was a noncompetitive inhibitor, with K_i = 6.2 × 10^?3 M and an IC₅₀ of 2.6 mM, whereas adenosine diphosphate was a competitive inhibitor, with K_i = 0.8 × 10^?3 M and an IC₅₀ of 8.3 mM. Glutathione, o-phenanthroline, zinc, and ethylenediamine tetraacetic acid (EDTA) inhibited PDE-I activity whereas Mg²⁺ slightly potentiated the activity. PDE-I hydrolyzed thymidine-5′-monophosphate p-nitrophenyl ester most readily, whereas cyclic 3′-5′-AMP was least susceptible to hydrolysis. PDE-I was not lethal to mice at a dose of 4.0 mg/kg, ip, but had an anticoagulant effect on human plasma. These findings indicate that W. aegyptia PDE-I shares various characteristics with this enzyme from other snake venoms.