title: pH-independent and -dependent cleavage of proinsulin in the same secretory vesicle.
abstract: By quantitative immunoelectron microscopy and HPLC, we have studied the effect of disrupting pH gradients, by ammonium chloride, on proinsulin conversion in the insulin-producing B-cells of the islets of langerhans. Proinsulin content and pH in single secretory vesicles were measured on consecutive serial sections immunostained alternately with anti-proinsulin or anti-dinitrophenol (to reveal the pH-sensitive probe DAMP) antibodies. Radioactivity labeled proinsulin, proinsulin cleavage intermediates, and insulin were quantitated by HPLC analysis of extracts of islets treated in the same conditions. Cleavage at the C-peptide/A-chain junction is significantly less sensitive to pH gradient disruption than that of the B-chain/C-peptide junction, but the range of pH and proinsulin content in individual vesicles indicate that both cleavages occur in the same vesicle released from the TGN.
authors.affiliation: Département de Morphologie, University of Geneva, Switzerland.
authors.forename: L
authors.initials: L
authors.lastname: Orci
authors.forename: P
authors.initials: P
authors.lastname: Halban
authors.forename: A
authors.initials: A
authors.lastname: Perrelet
authors.forename: M
authors.initials: M
authors.lastname: Amherdt
authors.forename: M
authors.initials: M
authors.lastname: Ravazzola
authors.forename: R G
authors.initials: RG
authors.lastname: Anderson
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D003594:Cytoplasmic Granules / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000378:metabolism*; D011384:Proinsulin / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000643:Ammonium Chloride; D011384:Proinsulin; D005947:Glucose