Immunochemical characterization of the MoAb F-104 epitope. (A) Epitope expression in purified Aα chain derivatives. The following antigens whose structures include Aα 487-498 were tested as solution phase competitors in the MoAb F-104 ELISA: TAM peptide (•); linear peptide (⧫); CNBr IX (Aα 477-517) (▪); plasmin-digested peptides (open symbols, dotted lines). The molar concentration of the octavalent TAM peptide was normalized to the number of moles of Aα 487-498/mole of peptide. Immunoreactivity is expressed as logit %B (see text). (B) Epitope expression in fibrinogen and its Aα chain plasmin derivatives. Purified fibrinogen (solid symbols and line), plasma fibrinogen from a single normal donor (solid symbols, dashed line), and Aα FDPs obtained from plasmin-treated purified fibrinogen (open symbols, dashed line) were assayed for F-104 immunoreactivity. Data are presented as in (A). The molar concentration of fibrinogen in the single donor plasma was derived from clottability measurements (3.45 mg/mL) and expressed as Aα chain equivalents (20,294 pmol/mL).