HK exon 7 products alters ¹²⁵I-thrombin binding sites/platelet. Gel-filtered platelets were incubated with 0.3 nmol/L ¹²⁵I-α-thrombin to measure the high-affinity binding sites per cell to assess the effect of peptides from D3 of HK on thrombin binding. The first bar shows specific thrombin binding, in the absence of peptides. The second bar shows specific binding in the presence of K²⁷⁰-Q²⁹² (100 μmol/L). The third bar shows specific binding in the presence of LNAENNA (100 μmol/L). The fourth bar shows specific binding in the presence of exon 9-coded peptide (100 μmol/L). Only products of exon 7 were able to block thrombin binding to the platelet high-affinity receptor for thrombin. The results are the mean ± SEM of six determinations in quadruplicate and, with the exception of the exon 9-coded peptide, are significantly different compared with the binding of thrombin alone (P < .05).