Biosynthesis of insulin in bovine fetal pancreatic slices: the incorporation of tritiated leucine into a single-chain proinsulin, a double-chain intermediate, and insulin in subcellular fractions.
This communication reports the biosynthesis of insulin in the bovine fetal pancreatic slices in vitro. Double-chain proinsulin and insulin were found as major components in the mitochondrial-granule fraction of bovine fetal pancreas. Tritiated leucine was incorporated into a single-chain proinsulin, a double-chain proinsulin, and insulin. Subcellular fractionation of the slices incubated with tritiated leucine showed that radioactive single-chain proinsulin was present in the deoxycholate-soluble microsomal fraction, deoxycholate-insoluble microsomal fraction, and mitochondrial-granule fraction. Labeled double-chain proinsulin and insulin were present in the deoxycholate-soluble microsomal and mitochondrial-granule fractions. These results are consistent with the hypothesis that insulin is synthesized as a single-chain polypeptide on the ribosomes, and that intracellular proteolysis in the subcellular membranous organelles and beta-granules converts the single-chain proinsulin to insulin via a double-chain intermediate.
D000818:Animals; D002417:Cattle; D002850:Chromatography, Gel; D005333:Fetus; D006651:Histocytochemistry; D007122:Immunoelectrophoresis; D066298:In Vitro Techniques; D007328:Insulin / Q000096:biosynthesis*; D007930:Leucine / Q000378:metabolism; D008854:Microscopy, Electron; D008928:Mitochondria; D010179:Pancreas / Q000378:metabolism*; D014316:Tritium
D007328:Insulin; D014316:Tritium; D007930:Leucine