title: Low structural specificity for nucleoside triphosphates as antagonists of ADP-induced platelet activation.
abstract: Although the platelet ADP receptor is thought to exhibit a high degree of structural selectivity, adenosine 5'-O-(thiotriphosphate) (ATP alpha S) is a potent inhibitor of ADP-induced platelet activation and has been recently shown to bind with high affinity (Kd 3 +/- 0.1 nM) to formaldehyde-fixed platelets and to be photoincorporated into an 18-kDa fragment beginning at Tyr-198 of glycoprotein (GP) IIb alpha (Greco, N. J., Yamamoto, N., Jackson, B. W., Tandon, N. N., Moos, M., Jr., and Jamieson, G. A. (1991) J. Biol. Chem. 266, 13627-13633). Further studies have now shown that guanosine 5'-O-(thiotriphosphate) (GTP alpha S) also binds to high affinity sites (Kd 4.7 +/- 0.9 nM; 13,600 +/- 1,140 sites/platelet) and to low affinity sites (Kd 470 +/- 85 nM; 135,900 +/- 19,400 sites/platelet). Competition binding studies showed that all GTP alpha S binding sites were accessible to ADP and vice versa. The corresponding pyrimidine nucleotide cytidine 5'-O-(thiotriphosphate) (CTP alpha S) was found to be similarly effective in competing in the binding of ADP and both 5'-O-(thiotriphosphates) as well as uridine 5'-O-(thiotriphosphate) (UTP alpha S) were potent inhibitors of platelet shape change and aggregation. Ultraviolet irradiation of platelets in the presence of either [35S]GTP alpha S or [35S]UTP alpha S resulted in their specific incorporation into the alpha chain of GPIIb as previously shown with [35S]ATP alpha S. These results show that the structure of the nucleotide base has little influence on its ability to occupy the ADP-binding site on platelets, to function as an inhibitor of ADP-induced activation or to be photoincorporated into GPIIb alpha.
authors.affiliation: American Red Cross, Cell Biology Laboratory, Rockville, Maryland 20855.
authors.forename: N J
authors.initials: NJ
authors.lastname: Greco
authors.forename: N N
authors.initials: NN
authors.lastname: Tandon
authors.forename: B W
authors.initials: BW
authors.lastname: Jackson
authors.forename: G A
authors.initials: GA
authors.lastname: Jamieson
mesh_terms: D000244:Adenosine Diphosphate / Q000037:antagonists & inhibitors / Q000097:blood / Q000494:pharmacology*; D001667:Binding, Competitive; D001792:Blood Platelets / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000097:blood; D006801:Humans; D007700:Kinetics; D015539:Platelet Activation / Q000187:drug effects*; D010974:Platelet Aggregation / Q000187:drug effects; D011983:Receptors, Purinergic / Q000187:drug effects / Q000502:physiology*; D012265:Ribonucleotides / Q000494:pharmacology*; D013873:Thionucleotides / Q000097:blood
chemical_list: D011983:Receptors, Purinergic; D012265:Ribonucleotides; D013873:Thionucleotides; D006153:Guanosine Diphosphate; D000244:Adenosine Diphosphate; C020339:guanosine 5'-O-(1-thiodiphosphate)