Qualitative evaluation of intact, α_E-containing fibrinogen in adult and fetal plasma. Plasma samples (same sources as used in lanes 2 and 3 of Fig 2) were subjected to SDS-PAGE under nonreducing conditions, transferred to nitrocellulose, and probed with either anti-VI (lanes 1 and 2) or anti-α (lanes 3 and 4) as described in Materials and Methods: lanes 1 and 3, adult (A); lanes 2 and 4, fetal (F ). For better comparison of their molecular species, plasma volumes analyzed in this Western blot were adjusted to minimize differences in band intensities. Lanes 3 and 4 each contained approximately 50 ng total fibrinogen. For lanes 1 and 2, more material was loaded (50 and 5 times, respectively) to obtain Fib₄₂₀ bands of similar intensity. A faint Fib₄₂₀ band can be seen above Fib₃₄₀ in lane 4 on overexposure of the film.