The F-104 epitope in fibrinogen includes a plasmin cleavage site as visualized by immunoblotting with MoAb F-102 (anti-Aα 563-578). Purified fibrinogen was digested with plasmin (see Fig 3 legend) either without (left) or with (right) an initial MoAb F-104 preincubation step. PVDF transfers from 12.5% SDS-PAGE (nonreduced) were subjected to immunoblotting with MoAb F-102; 9.6 μg (56 pmol Aα chain equivalents) of intact or plasmin-treated fibrinogen were applied to each lane. At this load application, COOH-terminal Aα chain degradation products present at low level in the starting fibrinogen preparation are visualized in the T₀ lanes. The high molecular weight material at the top of the lanes in the right panel reflects the F-104 IgG added during the preincubation step (16.8 μg, 113 pmol IgG/lane).