The pancreatic B cell has been used as a model to compare the release of newly synthesized prohormone/hormone with that of stored hormone. Secretion of newly synthesized proinsulin/insulin (labeled with [3H]leucine during a 5-min pulse) and stored total immunoreactive insulin was monitored from isolated rat pancreatic islets at basal and stimulatory glucose concentrations over 180 min. By 180 m...

The biological function of the connecting peptide (C-peptide) of proinsulin is unknown. Comparison of all known C-peptide sequences reveals the presence of a highly conserved peptide sequence, Glu/Asp-X-Glu/Asp (X being a hydrophobic amino acid), adjacent to the Arg-Arg doublet at the B chain/C-peptide junction. Furthermore, the next amino acid in the C-peptide sequence is also acidic in many a...

Biogenesis of the regulated secretory pathway in the pancreatic beta-cell involves packaging of products, notably proinsulin, into immature secretory granules derived from the trans-Golgi network. Proinsulin is converted to insulin and C-peptide as granules mature. Secretory proteins not entering granules are conveyed by transport intermediates directly to the plasma membrane for constitutive s...

There have been numerous attempts to study insulin biosynthesis by perfused pancreas slices and isolated islets of Langerhans, but so far insulin synthesis has rarely been successfully carried out with broken-cell preparation of islets or other subcellular fractions. Nevertheless, Wagle (1 965) showed that a pH 5 enzyme-microsomal fraction obtained from foetal dog pancreas incorporated *4C-labe...

Inosine, guanosine and adenosine strongly stimulated proinsulin biosynthesis and insulin secretion in isolated mouse pancreatic islets. None of the purine ribonucleosides stimulated insulin secretion in rat islets, although as reported [jain & Logothetopoulos (1977) Endocrinilogy 100, 923-927] inosine and guanosine, but no adenosine, were potent stimulants of proinsulin biosynthesis in this spe...

Improved understanding of the primary molecular events underlying NIDDM and obesity is essential if more effective therapies are to be devised. Individual susceptibility to these interrelated conditions is under genetic influence (1), and clues to the identity of the major aetiological genes may come from physiological studies that pinpoint candidate pathways. A characteristic feature of NIDDM ...

Proinsulin is a key autoantigen in type 1 diabetes. Evidence in the mouse has underscored the importance of the insulin B chain region in autoimmunity to pancreatic beta cells. In man, a majority of proteasome cleavage sites are predicted by proteasome cleavage algorithms within this region. To study CD8+ T cell responses to the insulin B chain and adjacent C peptide, we selected 8- to 11-mer p...

In neuronal and endocrine cells, peptide hormones are selectively segregated into storage granules, while other proteins are exported continuously without storage. Sorting of hormones by cellular machinery involves the recognition of specific structural domains on prohormone molecules. Since the propeptide of insulin is known to play an important role in its three-dimensional structure, it is r...

Human proinsulin C-peptide has been extracted from human pancreas with acid-ethanol and purified by means of gel filtration, carboxymethyl-cellulose chromatography, paper electrophoresis, and partition chromatography. The purified material was judged to be about 98% pure by compositional analysis. Amino acid sequence analysis was carried out on the intact C-peptide and fragments derived by hydr...

Although the enzymes that catalyze the transformation of proinsulin to insulin have not yet been identified, studies of intermediate forms of proinsulin isolated from bovine pancreas indicate the existence of a mechanism in which the interchain connecting peptide is cleaved with elimination of a pair of basic residues from each end to yield insulin and the intact remainder of the connecting pep...