ABSTRACT
The venom phosphodiesterase I (PDE-I, EC 3.1.4.1) is useful in the elucidation of the structure and nucleotide sequence of nucleic acids. In the present study, PDE-I was purified from Agistrodon bilineatus venom by preparative native-PAGE. A single protein band was observed in analytical native-PAGE. The enzyme also gave a single band in SDS-PAGE with a molecular mass of 140 kDa. The position of the band was not altered in the presence of β-mercaptoethanol, suggesting the protein did not contain subunits. The enzyme was free from 5’-nucleotidase and alkaline phosphatase activities. It showed a broad optimum pH range (9.0-11.0), whereas the optimum temperature was found to be 600C, with activity decreasing at >650C. Energy of activation (Ea) was calculated to be 0.31. The PDE-I was a glycoprotein having 14% of carbohydrate content. The Vmax, Km, Kcat and Ksp values of the enzyme were 3.85 μM/min/mg, 8.3 × 10-3 M, 23s-1 and 46.4 M-1 Min-1 respectively. Cysteine caused a non-competitive inhibition with a Ki 6.3 × 10−3 M (IC50 of 1.6 mM), whereas ADP caused a competitive inhibition having Ki 0.8 × 10−3 M (IC50 5.4 mM). Glutathione, o-phenanthroline, zinc and EDTA inhibited the enzyme activity, whereas Mg2+ slightly potentiated the activity. The enzyme hydrolyzed thymidine 5’-monophosphate p-nitro-phenyl ester most readily (10-fold), while 3’-5’-cAMP was least readily hydrolyzed substrate. The enzyme up to 4.0 mg/Kg i.p was not lethal in mice. It exhibited an anticoagulant effect, and increased the normal clotting time of normal citrated human plasma, whereas the crude venom showed strong coagulant effect. The above results showed that the A. bilineatus PDE-I was very similar to that isolated from other snake venoms. The purification procedure described here is simple, rapid and reproducible and may prove useful to isolate pure protein for investigation into the contribution of this enzyme to the biological activities of A. bilineatus venom and PDE-I insight, in general.