The rate and extent of fibrin cross-linking are not influenced by polyP. Fibrin cross-linking was examined using SDS-PAGE for reactions containing 2.6 mg/mL citrate-free fibrinogen (containing a small amount of contaminating factor XIII), which was preincubated for 15 minutes in the presence of 2.5 mM CaCl₂ with 1 mM polyP (+) or without polyP (−). Thrombin (1 nM) was then added, and reactions were stopped at the indicated times. (Left) M_r markers. (Right) Locations of fibrin chains (α, β, γ, cross-linked γ-γ dimers and cross-linked α chain polymers).