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A Comparison of Methods for the Isolation of Carcinoembryonic Antigen¹

Departments of Pathology and Biochemistry, University of Alabama Medical Center, Birmingham, Alabama 35294

Carcinoembryonic antigen (CEA) was isolated from a human tumor with 0.02 M sodium phosphate containing 0.14 M NaCl (pH 7.0) (saline) and further studied after treatment with perchloric acid or 8 M urea. Preparations of CEA obtained from saline homogenates and both methods of treatment were characterized by isoelectric focusing and gel filtration. Perchloric acid treatment resulted in an approximate 10-fold decrease in protein and a significant loss of CEA as compared to the saline- and urea-treated material. Isoelectric focusing revealed that the resultant CEA subpopulations were dependent upon the method of isolation. Urea- and saline-treated material showed complex isoelectric patterns that were quantitatively dissimilar. Perchloric acid-treated material showed a comparatively simple isoelectric pattern that was not significantly affected by electrofocusing in the presence of urea. Gel filtration on ACA 34 of the CEA obtained from each method of isolation resulted in two peaks of activity. The first peak corresponded to the void volume of the column, and the second peak coeluted with commercially available purified ¹²⁵I-labeled CEA. Centrifugation of the peaks obtained resulted in a significantly greater loss of CEA from the void peak of each isolation procedure. The amount of CEA lost from the void peaks following centrifugation differed with each method of isolation and suggested the presence of aggregates.

¹ Supported by USPHS Grants CA-15089, CA-16764, and CA-16430 from the National Cancer Institute; by Grant DE-2670 from the National Institute of Dental Research; and by Grant PDT-9B from the American Cancer Society. Presented at the Federation of American Societies for Experimental Biology, April 1977 (18).

² To whom requests for reprints should be addressed, at Department of Pathology, University of Alabama Medical Center, University Station, Box 189, Birmingham, Ala. 35294.

Received 6/24/77. Accepted 11/16/77.