Abstract
We have determined the concentrations of the secretory proteins amylase and chymotrypsinogen and the membrane proteins KDELr and rBet1 in COPII- and COPI-coated pre-Golgi compartments of pancreatic cells by quantitative immunoelectron microscopy. COPII was confined to ER membrane buds and adjacent vesicles. COPI occurred on vesicular tubular clusters (VTCs), Golgi cisternae, the trans-Golgi network, and immature secretory granules. Both secretory proteins exhibited a first, significant concentration step in noncoated segments of VTC tubules and were excluded from COPI-coated tips. By contrast, KDELr and rBet1 showed a first, significant concentration in COPII-coated ER buds and vesicles and were prominently present in COPI-coated tips of VTC tubules. These data suggest an important role of VTCs in soluble cargo concentration by exclusion from COPI-coated domains.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Amylases / metabolism*
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Animals
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Carrier Proteins / metabolism
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Chymotrypsinogen / metabolism*
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Coated Pits, Cell-Membrane / metabolism*
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Coated Pits, Cell-Membrane / ultrastructure
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Coatomer Protein
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Endoplasmic Reticulum / metabolism*
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Endoplasmic Reticulum / ultrastructure
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Golgi Apparatus / metabolism*
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Golgi Apparatus / ultrastructure
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Male
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Membrane Proteins / metabolism*
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Microscopy, Immunoelectron
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Pancreas / physiology*
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Pancreas / ultrastructure
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Phosphoproteins / metabolism
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Qc-SNARE Proteins
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Rats
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Rats, Wistar
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Receptors, Peptide / metabolism*
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Saccharomyces cerevisiae Proteins*
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Vesicular Transport Proteins*
Substances
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BET1 protein, rat
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Carrier Proteins
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Coatomer Protein
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KDEL receptor
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Membrane Proteins
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Phosphoproteins
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Qc-SNARE Proteins
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Receptors, Peptide
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SEC31 protein, S cerevisiae
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Saccharomyces cerevisiae Proteins
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Vesicular Transport Proteins
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Chymotrypsinogen
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Amylases