Immunoprecipitation of thrombin-activated C2 domain chimeras by IgG fraction from patient RS. Recombinant factor V constructs metabolically labeled with [³⁵S]methionine included rHFV des B, chimera 1A, chimera 2A, chimera 3A, chimera 7A, and chimera 5A. Samples were first incubated with 2 nmol/L thrombin for 1 minute at 37°C and then immunoprecipitated with either the polyclonal rabbit anti-human factor V antibody or the IgG fraction from patient RS, as shown. The immunoprecipitates were analyzed by 6% SDS-PAGE and visualized by autoradiography. A nonspecific, high-molecular-weight band (>200 kD) is seen in all the immunoprecipitations of conditioned media, including the control IgG fraction from pooled normal plasma. Molecular-weight standards are shown on the left, and the positions of the factor Va heavy chain and light chain on the right.