C-Terminal Sequence of the F′c Fragment of Human Gamma G Globulin

Abstract

ENZYME digestion of immunoglobulins with papain, first described by Porter¹, has proved to be a useful technique for obtaining biologically active fragments of the parent molecules. The fragments are readily separated into the antigen combining Fab fragments and the Fc fragment which, though devoid of antigen-combining activity, retains other biological properties shared by most _γG antibody molecules². After prolonged digestion of normal human gamma globulin with papain, there is progressive degradation of the Fc fragment. There remains, however, a rapidly migrating resistant segment of the Fc fragment known as the F′c fragment (F′c) (ref. 3). Despite the fact that tryptic peptide maps of F′c derived from pooled gamma globulin display the characteristic Gm “a” and “non-a” peptides⁴, this genetic factor cannot be demonstrated by serological methods capable of detecting Gm a activity in the Fc fragment. Apparently insufficient conformation is retained by the F′c fragment for expression of this allotypic activity, even though the primary molecular basis for it persists. Although none of the biological properties of the Fc fragment have been recovered in the F′c fragment⁴, it seems possible that the F′c region contributes to some other biological properties of antibodies such as complement complexing, binding to skin, and placental permeability. Consequently, further characterization of this fragment may yield information relating chemical structure to biological function.