Characterization of the immunochemical reactivity of fibrinogen fragments by competitive radioimmunoassay: An improved method of analysis

Published results on the immunochemical reactivities of fibrinogen and fibrinogen fragments with fibrinogen-elicited antibodies that had been fractionated on the basis of preferential interaction with A [Nagy, J. A., Meinwald, Y. C., and Scheraga, H. A. (1982),Biochemistry21, 1794–1806] and B [Nagy, J. A., Meinwald, Y. C., and Scheraga, H. A. (1985)Biochemistry24, 882–887] peptides of this bivalent antigen have been reinterpreted. First, the multivalent counterpart of the Scatchard analysis has been used to determine the intrinsic association constant for the interaction of antibody with [¹²⁵I]fibrinogen, the radiolabeled ligand used in subsequent competitive binding studies. Second, the corresponding affinity constant for native fibrinogen has been evaluated from the relevant competitive radioimmunoassays by means of a quantitative analysis that takes into account the bivalency of both the radiolabeled and native fibrinogen molecules. Finally, affinity constants for the interactions of various fibrinogen fragments with antibody are also obtained by the procedure, and their magnitudes rationalized in terms of the equilibrium coexistence of unreactive (disordered) and native (functional) states of the fibrinogen peptides.