Intermolecular Heterogeneity of the Carcinoembryonic Antigen

Summary

Studies were performed to determine the degree of heterogeneity within any one preparation of purified carcinoembryonic antigen (CEA) of the human digestive system and the variations in chemical composition between such preparations. Individual batches of CEA, isolated from hepatic metastases arising from adenocarcinomas of either the colon or stomach, were examined by a number of physicochemical and immunochemical parameters. Among the differences observed were the carbohydrate/protein ratio and the quantities of the individual amino acid and monosaccharide residues in the different purified preparations examined. These variations, in turn, were responsible for the secondary manifestations of heterogeneity observed upon gel electrophoresis. The polydisperse nature of the electrophoretic pattern of each of the purified CEA preparations upon alkaline polyacrylamide gel electrophoresis was largely due to variations in the sialic acid content of individual CEA molecules. In addition, the molecular size and antigenicity of the CEA varied, to some degree, from preparation to preparation. Nevertheless, colon tumors as a group were far more similar to one another than they were to the gastric tumor preparation studied. The observations made demonstrate the overall complexity of the structure of the CEA molecule, obtained from different sources, but they also serve to elucidate certain of the parameters by which this molecular moiety may be defined.