Localization of glycoproteins in insulin secretory granules by ultrastructural autoradiography

To determine whether or not the secretory granules of insulin-secreting cells contained glycoproteins, isolated rat pancreatic islets were incubated for 2 and 4 hr in a medium containing L-[3H]-fucose. Quantitative analysis of high-resolution electron microscopic autoradiographs of the insulin-secreting beta cells demonstrated that glycoproteins with fucose residues are contained within the insulin secretory granule.