CHARACTERIZATION OF FETAL SERUM 5'-NUCLEOTIDE PHOSPHODIESTERASE - A NOVEL FUNCTION AS A PLATELET-AGGREGATION INHIBITOR IN FETAL CIRCULATION

The study was performed to indicate the ADPase activity of 5'-nucleoti de phosphodiesterase (PDEase) from human umbilical cord blood serum an d demonstrates the effect of this enzyme on ADP-induced platelet aggre gation. The PDEase was purified by using p-nitrophenyl-5' -TMP as a su bstrate. The PDEase had a molecular weight of 128,000 daltons, and act ivity 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 compe titive inhibitor with a Ki value of 4.05x10(-5) M. The enzyme was mark edly inhibited by 1 mM EDTA. The ADPase activity of the PDEase was 7.7 9 nmol/min/mg protein. The hydrolized products of ADP by the PDE ase w ere AMP and phosphoric acid. The platelet aggregation by ADP was inhib ited by the addition of the PDEase in the platelet-rich plasma. (C) 19 98 Elsevier Science Ltd.