Similarities between the transferrin receptor proteins on human reticulocytes and human placentae

The transferrin receptor of the human reticulocyte was isolated by two different immunoaffinity procedures. These included indirect immunoprecipitation with a transferrin/anti-transferrin complex and direct immunoprecipitation with antiserum to purified transferrin receptor from placentae. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the receptor isolated from reticulocytes reveals a polypeptide at Mr = 94,000 identical in molecular weight with that of the placenta. A radioimmunoassay using purified 125I-labeled transferrin receptor from placentae and antiserum to transferrin receptor fails to distinguish any immunological differences between the reticulocyte and placental forms of the protein. In addition, proteolytic digests of both of these polypeptides with Staphylococcus aureus protease show identical proteolytic patterns, indicating similar sequences.