Crystalline Fc prepared in High Yield from Normal Human IgG

Abstract

CRYSTALLINE rabbit Fc fragment is simple to prepare in high yield from the corresponding IgG by cysteine-activated papain digestion¹. Although crystalline products can be obtained from human myeloma globulins, only one report² has hitherto appeared describing an analogous substance from normal human IgG. The conditions for digestion of normal rabbit or human IgG were markedly different. One-tenth the ratio of enzyme: antibody was used, and the reaction time was reduced from 16 h to 30 min for the human material. In our hands, although a solid human Fc was obtained by the method of Hershgold et al., the material did not crystallize, and the yield was low. We therefore decided to re-examine the cysteine-activated digestion conditions. The results are reported here, together with the finding that the crystalline Fc, obtained in high yield, may be principally of a single Gm allotype, reflecting the allotypy of the IgG 1.