title: A novel thrombin-reactive protein complex in human platelets.
abstract: Attempts were made to isolate a 74,000-dalton protein which specifically and competitively blocked platelet aggregation by thrombin (Ganguly, P., and Fossett, N. G. (1981) Blood 57, 343-352) by two independent affinity chromatography methods. The protein isolates showed a main band migrating slightly faster than albumin in gel electrophoresis under nondenaturing conditions. In the presence of sodium dodecyl sulfate, electrophoresis of protein preparations consistently revealed the presence of four polypeptides of 74,000, 55,000, 27,000, and 20,000 daltons. The results suggest that these polypeptides are probably present as a multiprotein complex in platelets. The 55,000-dalton protein, like the 74,000-dalton protein, inhibited thrombin-induced platelet aggregation, while aggregation induced by adenosine diphosphate or trypsin was not significantly affected. However, incubation of the 55,000-dalton protein with the 74,000-dalton protein prior to the addition of thrombin did not inhibit platelet aggregation by thrombin, while the individual components under the same conditions did. In fact, the two proteins in combination could significantly enhance platelet aggregation by thrombin. These results suggest the existence of a multiprotein complex in human platelets, the components of which may modulate the action of thrombin on platelet aggregation.
mesh_terms: D001792:Blood Platelets / Q000502:physiology*; D001798:Blood Proteins / Q000302:isolation & purification* / Q000502:physiology; D006801:Humans; D007700:Kinetics; D008970:Molecular Weight; D010974:Platelet Aggregation; D013917:Thrombin / Q000502:physiology
chemical_list: D001798:Blood Proteins; C037204:thrombin-reactive protein complex; D013917:Thrombin