Bovine pancreas; albumin thin sections; Immuno-ferritin localization of trypsinogen: GolgiJamieson, James DKraehenbuhl, J-P4/19/19663.25 in. x 4 in. Lantern SlidesOriginal Magnification: x20,000This was the first study to use immuno-EM to localize secretory proteins in pancreatic acinar cells. It showed that the RER cisternae, all compartments of the Golgi and all zymogen granules contained trypsinogen. We also demonstrated that trypsinogen was much more concentrated in zymogen granules than in the earlier compartments on the secretory pathway.still image