(Pro)insulin associates with Golgi membranes of pancreatic B cells.

The immunocytochemical demonstration of (pro)insulin on intracellular membrane compartments of the pancreatic B cell reveals that the immunolabeling detected by the protein A/gold method is associated, at the level of the Golgi apparatus, with the inner aspect of the cisternal membranes; on the secretory granules, by contrast, insulin immunoreactive sites predominate over the granule core, and very little immunoreactivity is associated with the granule membrane. The localization of (pro)insulin immunoreactivity on Golgi membranes is compatible with the presence, at this level, of specific binding sites for (pro)insulin, which could be related to the proteolytic processing or sorting out (or both) of these peptides on their way from the rough endoplasmic reticulum to the storage secretory granules.