Comparison of Fch and Fc Fragments of IgG3: Evidence of an Intra‐Chain S‐S Bridge in the Hinge of γ3 Chains

Abstract

The Fc and Fch fragments of human IgG3, appearing late and early during papain digestion, respectively, were antigenically and structurally compared. Only the Fch fragment reacted with an anti‐Fh (hinge region‐specific) antiserum; thus the main portion of the hinge region is split off during the formation of Fc fragments The Fch fragment has a higher content of inter‐chain S‐S bridges than the Fc fragments. The Fc fragments are probably a mixture of three related fragments. The Fch fragment appears to be more homogeneous, although there was hydrolysis at the C‐terminal site of the hinge region in some of the Fch chains. Evidence is presented that the γ3 chain bridge has an extra intra‐heavy‐chain disulphidc bridge at the C‐terminal end of the hinge region.