polyP influences clot turbidity to a much greater extent than does heparin. The final turbidities of clots formed with fibrinogen mixed with thrombin were quantified as described in “Measurements of clot turbidity.” Reactions contained 2.6 mg/mL fibrinogen preincubated for 15 minutes in the presence of: various heparin concentrations without CaCl₂ (□); various heparin concentrations with 2.5 mM CaCl₂ (○); various polyP concentrations with 2.5 mM CaCl₂ (▼); or various polyP concentrations with 2.5 mM CaCl₂ and 5 U/mL heparin (♦). Clotting was then initiated with 1 nM thrombin. Heparin and polyP concentrations are indicated on the x-axes. Data are mean plus or minus SE (n = 4).