Four secretory proteins synthesized by hepatocytes are transported from endoplasmic reticulum to Golgi complex at different rates.

Abstract

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.

Monitoring the kinetics of glycoprotein synthesis and secretion in the filamentous fungus Trichoderma reesei: cellobiohydrolase I (CBHI) as a model protein

“…There, faster translation rates have been measured, e. g. 4n5 aa s −" for influenza virus haemagglutinin in CHO cells (Braakman et al, 1991) and 6 aa s −" for apolipoprotein B-100 in Hep G2 cells (Bostro$ m et al, 1986). On the other hand, the minimum times of secretion for several mammalian proteins have been reported to be somewhat longer than that observed here, 20-30 min (Bostro$ m et al, 1986 ;Fries et al, 1984 ;Matlin & Simons, 1983). However, the intracellular retention half times of different mammalian glycoproteins vary to a great extent, from about 30 min to several hours (Bostro$ m et al, 1986 ;Fries et al, 1984 ;Lodish et al, 1983 ;Yeo et al, 1985).…”

“…On the other hand, the minimum times of secretion for several mammalian proteins have been reported to be somewhat longer than that observed here, 20-30 min (Bostro$ m et al, 1986 ;Fries et al, 1984 ;Matlin & Simons, 1983). However, the intracellular retention half times of different mammalian glycoproteins vary to a great extent, from about 30 min to several hours (Bostro$ m et al, 1986 ;Fries et al, 1984 ;Lodish et al, 1983 ;Yeo et al, 1985). In addition, the protein folding, maturation and transport processes in mammalian cells are dependent on the cell type and expression system used, as well as on external parameters such as temperature and stress conditions (Braakman et al, 1991).…”

The Low pH in Trans-Golgi Triggers Autocatalytic Cleavage of Pre-α-inhibitor Heavy Chain Precursor

“…These observations suggest that the bikunin and H3 precursors are cleaved in different compartments: the secretory vesicles and the trans-Golgi/ trans-Golgi network, respectively. The residence time of a secretory protein in the Golgi complex and the secretory vesicles is 5-20 min (26), indicating that the protein spends Ͻ10 min in the trans-Golgi (network). As judged by our in vitro experiments, this time would not be sufficient for efficient cleavage of proH3, given a pH in this part of the Golgi of about 6.0.…”

Thyroglobulin Transport along the Secretory Pathway

“…DISCUSSION It has been known for some years that each secretory protein species exits the ER with its own distinct rate (45,46). The time spent preparing newly synthesized secretory proteins for export from the ER is thought to be comprised of two kinds of activities.…”