Proceedings: Interrelationship of carcinoembryonic antigen and colon carcinoma antigen-3.

Summary For the preparation of carcinoembryonic antigen from 0.5 to 5.0 kg of liver metastasis of colon carcinoma, a method is described which includes extraction with perchloric acid, column chromatography with the use of mixed-bed ion-exchange cellulose, and gel filtration. Carcinoembryonic antigen isolated from different individual tumors was interchangeable in the radioimmunoassay and demonstrated homology of the protein moiety, while differences in the carbohydrate portion are probably due to damage caused by autolysis. An additional step was required in the preparation of colon carcinoma antigen-III; polyacrylamide electrophoresis appeared to yield purified antigen. A comparison of the immunological and chemical properties of carcinoembryonic antigen versus those of colon carcinoma antigen-III showed them to be closely related glycoproteins which do not cross-react in radioimmunoassay. A radioimmunoassay was developed to determine colon carcinoma antigen-III concentration, and the normal titer in plasma ranges from 0.7 to 1.5 µg/ml.