In the previous paper we described an in vitro system of guinea pig pancreatic slices whose secretory proteins can be pulse-labeled with radioactive amino acids. From kinetic experiments performed on smooth and rough microsomes isolated by gradient centrifugation from such slices, we obtained direct evidence that secretory proteins are transported from the cisternae of the rough endoplasmic reticulum to condensing vacuoles of the Golgi complex via small vesicles located in the periphery of the complex. Since condensing vacuoles ultimately become zymogen granules, it was of interest to study this phase of the secretory cycle in pulse-labeled slices. To this intent, a zymogen granule fraction was isolated by differential centrifugation from slices at the end of a 3-min pulse with leucine-14C and after varying times of incubation in chase medium. At the end of the pulse, few radioactive proteins were found in this fraction; after +17 min in chaser, its proteins were half maximally labeled; they became maximally labeled between +37 and +57 min. Parallel electron microscopic radioautography of intact cells in slices pulse labeled with leucine-3H showed, however, that zymogen granules become labeled, at the earliest, +57 min post-pulse. We assumed that the discrepancy between the two sets of results was due to the presence of rapidly labeled condensing vacuoles in the zymogen granule fraction. To test this assumption, electron microscopic radioautography was performed on sections of zymogen granule pellets isolated from slices pulse labeled with leucine-3H and subsequently incubated in chaser. The results showed that the early labeling of the zymogen granule fractions was, indeed, due to the presence of highly labeled condensing vacuoles among the components of these fractions.
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1 August 1967
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August 01 1967
INTRACELLULAR TRANSPORT OF SECRETORY PROTEINS IN THE PANCREATIC EXOCRINE CELL : II. Transport to Condensing Vacuoles and Zymogen Granules
James D. Jamieson,
James D. Jamieson
From The Rockefeller University, New York 10021
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George E. Palade
George E. Palade
From The Rockefeller University, New York 10021
Search for other works by this author on:
James D. Jamieson
From The Rockefeller University, New York 10021
George E. Palade
From The Rockefeller University, New York 10021
Received:
February 20 1967
Online ISSN: 1540-8140
Print ISSN: 0021-9525
Copyright © 1967 by The Rockefeller University Press
1967
J Cell Biol (1967) 34 (2): 597–615.
Article history
Received:
February 20 1967
Citation
James D. Jamieson, George E. Palade; INTRACELLULAR TRANSPORT OF SECRETORY PROTEINS IN THE PANCREATIC EXOCRINE CELL : II. Transport to Condensing Vacuoles and Zymogen Granules . J Cell Biol 1 August 1967; 34 (2): 597–615. doi: https://doi.org/10.1083/jcb.34.2.597
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