Characterization and subunit analysis of ferritin isolated from normal and malignant human liver

Ferritin was purified from normal, fetal, and malignant liver tissue. Ferritin purified from hepatoma tissue migrated slightly faster than normal human liver ferritin in polyacrylamide gel electrophoresis. Hepatoma and fetal liver ferritin contained an acidic components in gel and liquid isoelectric focusing not found in normal liver ferritin. We have called it a carcinofetal isoferritin. The subunit compositions of ferritins purified from human liver cell carcinoma and normal liver were then compared. Both ferritin consisted of a subunit species with an identical molecular weight of approximately 18,500. A single subunit of similar molecular weight was also demonstrable after dissociation of 8 M urea and by gel filtration in urea. Two subunits were demonstrable in normal liver ferritin by means of acrylamide electrophoresis in 8 M urea in acid pH. The same two subunits were also demonstrable in ferritin isolated from human liver cell carcinoma. However, a third subunit, intermediate in charge between the two normal liver subunits, was demonstrable in different amounts in ferritins from two hepatomas. Ferritins from normal and malignant livers were immunologically indistinguishable. The tumor-specific acidic isoferritin was isolated and antisera were prepared. The isolated acidic isoferritin was found to be immunologically identical to normal liver isoferritins. It is concluded that the multiple isoferritins of the human liver ferritin consist of two subunits, which are identical in molecular weight but which differ in net charge. Ferritin, isolated from two human liver carcinoma tissues, was composed of the same two subunits and a third unique subunit. Different amounts of these subunits may account for the several normal isoferritins and a unique tumor-specific acid isoferritin found in hepatoma.