Characterization of Fetal Serum 5′-Nucleotide Phosphodiesterase: A Novel Function as a Platelet Aggregation Inhibitor in Fetal Circulation

Abstract

The study was performed to indicate the ADPase activity of 5′-nucleotide phosphodiesterase (PDE-ase) from human umbilical cord blood serum and demonstrates the effect of this enzyme on ADP-induced platelet aggregation. The PDEase was purified by using p-nitrophenyl-5′-TMP as a substrate. The PDEase had a molecular weight of 128,000 daltons, and activity of 103 nmol/min/mg protein. The PDEase activity was inhibited by 5′-AMP, ADP, ATP. But 2′-AMP, 3′-AMP, 3′:5′ cAMP, and adenosine had no inhibiting effects. Kinetic analysis indicated that ADP was a competitive inhibitor with a K i value of 4.05×10 −5 M. The enzyme was markedly inhibited by 1 mM EDTA. The ADPase activity of the PDEase was 7.79 nmol/min/mg protein. The hydrolized products of ADP by the PDEase were AMP and phosphoric acid. The platelet aggregation by ADP was inhibited by the addition of the PDEase in the platelet-rich plasma.