Radioactive iodination of lymphocyte surface proteins and characterization of their molecular properties.

Two radioiodination methods for surface proteins on mouse lymphocyte membrane, that is, the lactoperoxidase method and the chloramine T method, were comparatively investigated. The extents of iodination under various conditions were determined by measurements of radioactivities incorporated into the cell fractions and into the protein components isolated by specific immunoprecipitation from lyzates of the labeled cells. It was demonstrated that the chloramine T method, as well as the lactoperoxidase method, was applicable to label the lymphocyte surface proteins without any significant labeling of the cytoplasmic proteins. It was also found that the iodination efficiencies of the membrane immunoglobulin polypeptide chains in these two labeling methods were different in each of the isotopes, mu and delta chains. The possibility that the differences are related to their primary structures and to their exposure or anchorage profiles on the cell membrane is discussed with reference to the reaction mechanisms of the two labeling methods.