Fibrinogen purified from adult and fetal sources: Disproportionately higher amount of α_E chains in fetal material. Fibrinogen (I-2 fraction) was purified18 from plasma derived from normal adult blood (A) and umbilical cord (ie, fetal) blood (F ). The material was separated by SDS-PAGE (80 μg per lane) under reducing conditions and transferred to nitrocellulose. Lanes 1 and 2 were stained with Amido Black (Sigma); lanes 3 and 4 were treated with anti-VI, followed by HRPO-labeled antimouse IgG, and developed with chloronaphthol. Lanes 1 and 3, adult; and lanes 2 and 4, fetal. Positions of the individual chains are indicated. Overloading the gel enabled the Fib₄₂₀-specific α_E chain to be seen by protein staining as a faint band in lane 2 on the original blot.