Phosphodiesitrase activity of some Egyptian snake venoms: biochemical and immunological characteristics and effect on blood coagulation of phosphodiesterase enzyme from Naja nigricollis venom

Phosphodiesterase (PDE) enzyme activity was screened in four Egyptian snake venoms belonging to families Elapidae and Viperadae and a highly active enzyme (Nn-PDEII), from the richest snake venom species Naja nigricollis, was purified and characterized in a set of biochemical, immunological and biological assays. Purification was followed in two successive steps including gel filtration and ion exchange chromatography. The enzyme exists as a dimer with a disulphide bridge between the two subunits. The enzyme showed its optimum activity at 60 C and pH 8 and was best stable in alkaline medium (pH 8-9) at 40 C up to 1 h, however, it loses ~50% of its activity at 60 C. PDE activity was markedly increased by Mn, Co and Mg , increased to a lesser extent by Ca, Ba, Ni, K and Na but not significantly affected by Zn ions and iodoacetic acid. On the other hand, Al and Cu ions, PMSF, DTT, EDTA, O-phenanthroline and L-cysteine exhibited obvious inhibitory effects. NnPDEII was highly immunogenic to rabbits and could induce antibodies specific to N. nigricollis venom antigens. In addition, anti-PDEII antibodies were able to partially neutralize, in vitro, PDE activity of the enzyme in a dosedependent manner. Nn-PDEII exhibited potent anticoagulant effect most probably via inhibiting one or more of the coagulation factors within the intrinsic pathway in the coagulation cascade. Characterization of a component of N. nigricollis venom that affect blood coagulation at specific stage could have potential in identifying new drug leads in the treatment of hemostatic disorders.