Characterization of nascent and secreted thyroxine-binding globulin in cultured human hepatoma (Hep G2) cells.

摘要: Thyroxine-binding globulin (TBG) synthesis by human hepatoma (Hep G2) cells was demonstrated pulse labeling with [35S]methionine or [3H]mannose and subsequent immunoprecipitation in the medium cell lysate. Secreted TBG glycosylated had same apparent molecular weight sodium dodecyl sulfate-polyacrylamide gel electrophoresis as purified from serum. Pulse-chase experiments failed to show any precursor form intracellularly. Treatment of amino acid analogs, canavanine thialysine, did not cause secretion large-molecular-weight moieties, contrast what observed case albumin. activity, assessed [125I]thyroxine anti-TBG serum, detectable media oocytes injected RNA Hep G2 cells. Translation this rabbit reticulocyte lysate, followed revealed a protein having electrophoretic mobility deglycosylated serum (Mr approximately 45,000). Since still contains 3% its carbohydrate, it appears that translation product an additional fragment (signal peptide) about 1,500 daltons. It is unlikely, however, synthesized via larger-molecular-weight precursor.