title: Characterization of a plasmin-digest fragment of rabbit immunoglobulin gamma that binds antigen and complement.
abstract: Rabbit immunoglobulin gamma (IgG) was digested with plasmin after being left for 15 min at pH2.5, 30 degrees C followed by a rapid increase in the pH to 7. The fragment antigen and complement binding (Facb) was isolated and characterized chemically and biologically. Sequence studies showed that the C-terminal quarter of the heavy chain had been removed, the split occurring at a lysine-alanine bond in the sequence Thr-Ile-Ser-Lys-Ala-Arg. The fragment Facb retained the capacity to precipitate with antigen and the precipitate caused activation of the first component of complement of the same order as that of acid-treated IgG. Both Facb and acid-treated IgG showed a fall in complement fixation relative to the native molecule of 30-40%.
mesh_terms: D000478:Alkylation; D000595:Amino Acid Sequence; D000818:Animals; D000941:Antigens; D002268:Carboxypeptidases; D003168:Complement Fixation Tests; D003165:Complement System Proteins; D003488:Cyanogen Bromide; D005341:Fibrinolysin; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007128:Immunoglobulin Fragments / Q000302:isolation & purification*; D007074:Immunoglobulin G / Q000032:analysis*; D011817:Rabbits; D014357:Trypsin
chemical_list: D000941:Antigens; D007128:Immunoglobulin Fragments; D007074:Immunoglobulin G; D003165:Complement System Proteins; D002268:Carboxypeptidases; D014357:Trypsin; D005341:Fibrinolysin; D003488:Cyanogen Bromide