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.
pH-independent and -dependent cleavage of proinsulin in the same secretory vesicle.
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L Orci, P Halban, A Perrelet, M Amherdt, M Ravazzola, R G Anderson; pH-independent and -dependent cleavage of proinsulin in the same secretory vesicle.. J Cell Biol 1 September 1994; 126 (5): 1149–1156. doi: https://doi.org/10.1083/jcb.126.5.1149
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