= Pancreatic secretory-protein pulse-chase experiment
In 1967, <James D. Jamieson> and <George E. Palade> incubated guinea pig <pancreas> slices, following a three-minute pulse of tritium-labeled <leucine> with excess unlabeled <leucine>. This <pulse-chase analysis> marked newly made <proteins> while reducing subsequent incorporation. Fixed, Epon-embedded thin sections were mounted on coated grids, covered with Ilford L-4 photographic emulsion, developed and stained for <electron microscopy>. <Autoradiography> located photographic grains relative to <pancreatic acinar cell> structures.<Intracellular Transport of Secretory Proteins in the Pancreatic Exocrine Cell. II. Transport to Condensing Vacuoles and Zymogen Granules by James D. Jamieson and George E. Palade>[Jamieson and Palade, Intracellular Transport of Secretory Proteins in the Pancreatic Exocrine Cell. II. Transport to Condensing Vacuoles and Zymogen Granules (1967), p. 598 Methods; Figure 10: three-minute pulse]{ref}
Pulse-end samples provided a temporal reference: label lay mainly over <rough endoplasmic reticulum>; later samples shifted toward peripheral <Golgi apparatus> elements, condensing vacuoles and <secretory granules>. As a contamination check, isolated granule pellets were also examined by <autoradiography>: early pellet labeling chiefly marked condensing vacuoles. Grids from the compared pellet samples were coated together to control photographic processing. This supported transport of a previously labeled cohort rather than separate synthesis at each location. Fixed samples did not track individual <proteins>; localization was finite, and labeling was not absolutely exclusive to secretory cargo. The result concerns this preparation, not every <protein> in every <biological cell>.<Intracellular Transport of Secretory Proteins in the Pancreatic Exocrine Cell. II. Transport to Condensing Vacuoles and Zymogen Granules by James D. Jamieson and George E. Palade>[pp. 603–606 and Figures 10–13: changing localization; pp. 610–611 and Figures 14–15, Table III: pellet check and matched emulsion processing; p. 611 General Premises: nonexportable-protein labeling]{ref}
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