Abstract
Three cases of congenital sucrase-isomaltase deficiency in man were investigated by pulse-labelling of biopsy specimen in organ culture with 35S-methionine and by measurement of enzyme activity. Sucrase activity was either completely absent or drastically reduced. Isomaltase activity was in all cases 1/10 of that found in normals. Pulse-labelling followed by immunoprecipitation of SI with monoclonal antibodies revealed only the high-mannose precursor forms. In fact, the polypeptides precipitated from the 30 min and 4 h labelled biopsies were equally sensitive to endoglycosidase H (endo H). In normal controls, the complex glycosylated, endo H-insensitive form of SI was the predominant species after 4 h pulse.
Conclusions: These findings suggest that SI is synthesized but did not acquire complex carbohydrates in the Golgi and consequently is not further transported to the microvillus membrane. These results correlate well and extend those found by immuno-electronmicroscopic localization of the SI precursors in one of the biopises studied here.
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Naim, H., Sterchi, E., Hauri, H. et al. DEFECTIVE POSTTRANSLATIONAL PROCESSING OF SUCRASE-ISOMALTASE (SI) IN CONGENITAL SUCRASE-ISOMALTASE DEFICIENCY. Pediatr Res 20, 693 (1986). https://doi.org/10.1203/00006450-198607000-00048
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DOI: https://doi.org/10.1203/00006450-198607000-00048