Biosynthesis, intracellular processing and secretion of haptoglobin in cultured rat hepatocytes.
Biosynthesis, intracellular processing and secretion of the hetero-tetrameric (alpha 2 beta 2) glycoprotein, haptoglobin, were studied in primary cultured rat hepatocytes. The results obtained from pulse-chase experiments demonstrated that haptoglobin was initially synthesized as a larger precursor (pro-form), a single polypeptide chain comprising both the alpha- and beta-subunits, and immediately cleaved into subunits during intracellular transport, although about 8% of the newly synthesized haptoglobin was secreted as a pro-form. Monensin which impedes the secretory process at the Golgi complex blocked the complete glycosylation of beta-subunit but rather accelerated the conversion of the pro-form to subunits. These results indicate that the proteolytic processing of the haptoglobin precursor takes place at an early stage before the Golgi complex of the intracellular transport.
D000818:Animals; D002478:Cells, Cultured; D006242:Haptoglobins / Q000235:genetics* / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008985:Monensin / Q000494:pharmacology; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D051381:Rats; D011919:Rats, Inbred Strains
D006242:Haptoglobins; D008985:Monensin