Synthesis and migration of proteins in the cells of the exocrine pancreas as revealed by specific activity determination from radioautographs.

Radioautographs of pancreatic acinar cells were prepared in rats and mice sacrificed at various times after injection of leucine-, glycine-, or methionine-H(3). Measurements of radioactivity concentration (number of silver grains per unit area) and relative protein concentration (by microspectrophotometry of Millon-treated sections) yielded the mean specific activity of proteins in various regions of the acinar cells. The 2 to 5 minute radioautographs as well as the specific activity time curves demonstrate protein synthesis in ergastoplasm.

Migration of proteins along the axons of the sciatic nerve.

Soon after single or repetitive injections of leucine-H(3) in rats, an intense radioautographic reaction was seen over the nerve cell bodies, while the axons of the myelinated fibers of the sciatic nerve were insignificantly labeled. Later, however, these axons showed strong radioactivity, which at 4 days was located in a proximal and at 16 days in a distal region of the nerve. It was concluded that the protein synthesized in the nerve cell bodies of the sciatic nerve had migrated along its axons.

Continuous protein synthesis in nuclei, shown by radioautography with H3-labeled amino acids.

Radioautographic investigation of the cell nuclei of adult mice after injection of leucine-H(3), methionine-H(3), or glycine-H(3) shows a high uptake of tritium by chromatin material but not by nucleoli. It is concluded that protein synthesis occurs continuously within nuclear chromatin.