Preparation of an active Fd fragment by cyanogen bromide cleavage of an IgG heavy chain from a homogeneous rabbit antibody

The Fd fragment of a homogeneous rabbit antibody to type III pneumococcal polysaceharide has been prepared directly from the heavy chain by cleavage with cyanogen bromide. Cyanogen bromide cleavage of heavy chain produces Fd in 50–60% yield, free of the usual light chain contaminant. Fd combined with its homologous light chain to form an Fab fragment that had antigen binding activity indistinguishable from the recombinant of native light and heavy chains.