Abstract
The posttranslational processing of SI was investigated in organ culture of human intestinal biopsies labelled with 35S-methionine and immunoprecipitated with monoclonal antibodies. SI is synthesized as a high mannose precursor molecule of Mr 210,000 which is slowly converted in the Golgi to the complex glycosylated form of Mr 245,000. The half-time for the conversion of the Mr 210,000 to the Mr 245,000 is about 2 h. Owing to the absence of pancreatic secretions in the culture medium, only pro-SI and neither of the subunits S or I can be identified by SDS-PAGE. Trypsin, when added to homogenates from biosynthetically labelled biopsies, cleaved pro-SI to its subunits. Elastase and chymotrypsin were not effective. Based on this finding the transit time of pro-SI from the Golgi to the brush border membrane was estimated. In the presence of trypsin, the appearance of S and I and the decrease in the labelling intensity of pro-SI was observed after 2 h of chase. This is indicative for a membrane insertion of pro-SI and its exposure to trypsin in the culture medium. The half-time for the conversion of pro-SI by the aid of trypsin to S and I was between 30 min and 1 h which corresponds to the transit post Golgi-time.
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Naim, H., Sterchi, E. & Lentze, M. 94. KINETICS OF THE PROCESSING OF NEWLY SYNTHESIZED SUCRASE-ISOMALTASE (SI) IN ORGAN CULTURES OF HUMAN INTESTINAL BIOPSIES. Pediatr Res 22, 111 (1987). https://doi.org/10.1203/00006450-198707000-00115
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DOI: https://doi.org/10.1203/00006450-198707000-00115
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