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.