BIOSYNTHESIS OF MUCINS (MUC2-6) ALONG THE LONGITUDINAL AXIS OF THE HUMAN GASTROINTESTINAL-TRACT

Little is known about the biosynthesis of mucin molecules in humans. O ur aim was to examine the mucin biosynthesis (MUC2-6) along the longit udinal axis of the healthy human gastrointestinal tract. Biopsies of h uman stomach and small and large intestine were metabolically labeled with S-35-labeled amino acids, [S-35]sulfate, or [H-3]galactose, immun oprecipitated with antibodies against MUC2-6, and analyzed by reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). MUC5AC [apparent molecular weight (M-r) 500,000] and MUC6 (apparent M -r 400,000) were detected in the stomach but not in the small or large intestine, MUGS (apparent M-r 550,000) was detected in duodenum and j ejunum, MUC2 (apparent M-r 600,000) was detected throughout the small and large intestine, and MUC4 (apparent M-r >900,000) was detected pre dominantly in the large intestine. Interestingly, some individuals dis played double bands of MUC2 and MUGS precursors, suggesting allelic va riation within the respective genes. Between small and large intestine mature secreted MUC2 showed differences in mobility on SDS-PAGE, sugg esting differences in glycosylation. Each of the MUC2, MUGS, MUC4, MUC 5AC, and MUC6 precursors could be distinguished electrophoretically, a nd each showed region-specific expression along the gastrointestinal t ract.