Four secretory proteins synthesized by hepatocytes are transported from endoplasmic reticulum to Golgi complex at different rates.
Pulse-chase experiments in conjunction with subcellular fractionation and quantitative immunoprecipitation have been used to study the intracellular transport of four secretory proteins, albumin, transferrin, prealbumin and retinol-binding protein, in isolated rat hepatocytes. The proteins were found to be transported from the endoplasmic reticulum (ER) to the Golgi complex (GC) at greatly different rates (t1/2 = 14-137 min), indicating that transport of secretory proteins between these organelles is effected by a selective, possibly receptor-mediated process and not through bulk phase transfers. The transport from the Golgi complex to the medium was rapid for all proteins (t1/2 approximately 15 min) and possibly occurred at the same rate. Consistent with these kinetic data, the amount of a rapidly transported protein (albumin) in the GC fraction was found to be high (relative to its amount in the ER fraction) whereas the amount of a slowly transported protein (transferrin) in the GC fraction was found to be low, as determined by radioimmunoassays.
D000818:Animals; D002458:Cell Fractionation; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008297:Male; D011228:Prealbumin / Q000235:genetics; D011499:Protein Processing, Post-Translational; D011506:Proteins / Q000235:genetics*; D051381:Rats; D011919:Rats, Inbred Strains; D012177:Retinol-Binding Proteins / Q000235:genetics; D012709:Serum Albumin / Q000235:genetics; D013347:Subcellular Fractions / Q000378:metabolism; D014168:Transferrin / Q000235:genetics
D011228:Prealbumin; D011506:Proteins; D012177:Retinol-Binding Proteins; D012709:Serum Albumin; D014168:Transferrin