Epitope mapping anti–factor V antibodies with recombinant factor V (rHFV) deletion mutants. Recombinant mutants, depicted schematically on the left side of the figure, included a mutant lacking amino acids 811 through 1491 of the B domain (rHFV des B), and a mutant lacking amino acids 811 through 1491 and residues Gly-2037 through Tyr-2196 of the light chain (rHFV des B/C2). The isolated heavy chain consists of amino acids Ala-1 through Arg-709 (rHFV HC); the isolated light chain consists of amino acids Ser-1546 through Tyr-2196 (rHFV LC); the isolated A3 domain consists of amino acids Ser-1546 through Arg-1877 (rHFV A3); and the isolated C2 domain consists of amino acids Gly-2037 through Tyr-2196 (rHFV C2). The IgG fractions purified by protein A-Sepharose chromatography are listed on the right side of the figure. Immunoprecipitation of [³⁵S]methionine metabolically labeled mutants and analysis by SDS-PAGE was performed as previously described.23 +, the IgG fraction immunoprecipitated the specific factor V mutant; −, it did not. ND, not done.