EVIDENCE FOR INTRAGRANULAR PROCESSING OF PRO-OPIOCORTIN IN THE MOUSE PITUITARY INTERMEDIATE LOBE

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  • 1 January 1981
    • journal article
    • research article
    • Vol. 26  (1) , 177-183
Abstract
Mouse pituitary neurointermediate lobes were pulse-incubated in [3H]Arg or [3H]Lys for 10 min and then chase-incubated for periods 0-4 h. The labeled peptides from the lobes were analyzed by immunoprecipitation with specific antisera, and thereafter, by acid-urea polyacrylamide gel electrophoresis. Using this paradigm, the synthesis of a prohormone common to ACTH and endorphin was detected in 10 min pulse labeled lobes. Following a chase period, processing of the prohormone to several forms of ACTH (MW 25,000, 23,000 and 13,000), .beta.-lipotropin and .beta.-endorphin was observed. To determine the intracellular site of processing of the prohormone, subcellular fractionation studies of labeled lobes were carried out. Analysis of the fractions from the pulse-labeled lobes revealed that the newly synthesized labeled prohormone was primarily localized in a granule-enriched fraction. In lobes that were pulsed and then chase-incubated for 1 h, there was a decrease in the amount of prohormone and an appearance of processed products in the granule-enriched fraction. In another paradigm, where the secretory granule-fraction was isolated from pulse-labeled lobes and then incubated in vitro for 6 h at pH 5.5, processing of the endogenous labeled prohormone within the isolated granule fraction was observed. In the mouse neurointermediate lobe, the ACTH/endorphin prohormone (pro-opiocortin) apparently is rapidly packaged into secretory granules after synthesis and processed intragranularly.