Inhibition of thrombin clotting time and HCII 1-75-thrombin binding assays by HV3 peptides and HCII 1-75. Panel A depicts three synthetic peptides schematically. All contain HV3 residues 54-66 (sequence shown exploded, above first HV354-66 bar), shown as a black bar (with “HV3” inset in white) with an MGS tripeptide on the N-terminus, without (HV354-66) hexahistidine or hexaglycine components or with only hexahistidine (H6HV354-66) or with both hexahistidine and hexaglycine components (H6HV354-66G6). Panel B shows the Thrombin Clotting Time (TCT) in seconds; diluted citrated human plasma was recalcified in the presence of thrombin and increasing concentrations of competitor peptides identified at right. The mean ± SD of 3 to 4 determinations is shown. Panel C shows binding of α-thrombin to immobilized HCII 1–75, expressed as the ratio of the absorbance at 490 nm in the presence of competitor (A) to that in its absence (A0); competitor peptides are identified at right. The mean ± SD of 5 to 6 determinations is shown.