Conversion of proglucagon in pancreatic alpha cells: the major endproducts are glucagon and a single peptide, the major proglucagon fragment, that contains two glucagon-like sequences.

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Abstract
Biosynthetic labeling studies show that glucagon is synthesized in mammalian islets via an 18-kDa [kilodalton] precursor, proglucagon, that during processing gives rise to glucagon and a secreted peptide of 10 kDa (the major proglucagon fragment, MPGF). A simple procedure was developed for the isolation of this peptide from rat pancreatic islets and have characterized it more fully. On the basis of its amino acid composition, MPGF is identified as the COOH-terminal portion of proglucagon that contains 2 glucagon-related sequences. These sequences do not appear to be liberated from MPGF in .alpha. cells of the islets of Langerhans but MPGF may be processed further elsewhere in the body or in other cells of the gastrointestinal tract that produce glucagon precursors.