Location of peptide fragments in the fibrinogen molecule by immunoelectron microscopy.

Antibodies to the disulfide knot fragment of bovine fibrinogen have been used to locate the site of this fragment within the intact fibrinogen molecule. The antibodies were isolated from rabbit antifibrinogen antisera by affinity chromatography. Electron micrographs of reaction mixtures of bovine fibrinogen and antibodies against the disulfide knot fragment showed pairs of fibrinogen molecules crosslinked by antibody molecules as well as higher order antibody-fibrinogen complexes. From an electron microscopic investigation of the crosslinked material, we conclude that the disulfide knot lies within the central nodule of the trinodular fibrinogen molecule. Antibodies to fragment H were used in the same manner to locate this fragment within the outer nodules of the human fibrinogen molecule.