Carcinoembryonic antigen: isolation of a sub-fraction with high specific activity

Four sub-fractions of carcinoembryonic antigen have been obtained by chromatography of conventional CEA on Con A-Sepharose and their immunoreactive contents have been determined. Comparative studies have shown that a fraction eluted with 2% methyl glucoside (CEA 2B) had the highest activity, with a potency (60 u/mug) twice that of unfractionated CEA although appreciable activity was also found in the other fractions. The amino acid composition of CEA 2B is similar to that reported for conventional CEA but there is a lower content of neutral hexoses and a comparatively high content of N-acetylglucosamine. Experiments with a pool of sera from 11 patients with colonic cancer, which had been fractionated on Con A-Sepharose, have shown that nearly all the CEA activity was contained in a fraction eluted with 2% methyl glucoside. A convenient method of isolating CEA with high specific activity directly from perchloric acid extracts of tumour tissue is also described.