A comparison of membrane proteins of normal and transformed cells by lactoperoxidase labeling.

The enzyme lactoperoxidase (iodide:hydrogen-peroxide oxidoreductase, EC 1.11.1.8) was used to iodinate ((125)I) accessible proteins on membranes of intact virally transformed and untransformed cells. A number of labeled bands of proteins were detected by acrylamide gel electrophoresis. A heavily labeled band with a molecular weight of approximately 250,000 daltons was found in all untransformed cells but was absent from transformed cells. When Coomassie-blue-stained membrane preparations were compared, a band was seen in normal cells which co-migrated with the lactoperoxidase-labeled band. In transformed cell membranes, three discrete bands were present in the same position. Thus, the expression of this protein may be altered when cells are in the transformed state.