The biosynthesis of intestinal mucins. The effect of salicylate on glycoprotein biosynthesis by sheep colonic and human gastric mucosal tissues in vitro

Abstract

1. Incubation of sheep colonic mucosal scrapings in Krebs–Ringer buffer for 2½hr. in the presence of salicylate (15mm) resulted in decreased incorporation of radioactivity into the epithelial glycoprotein from the following labelled precursors: 16·6μm-d-[2−¹⁴C]glucose (83·9% inhibition), 20μm-l-[U−¹⁴C]threonine (82%) and ³⁵SO₄²⁻(79%). Oxygen uptake measured simultaneously was diminished to 41% of the control value. 2. At lower concentrations of salicylate (e.g. 3·75mm), incorporation of 20μm-l-[U−¹⁴C]threonine was little affected (3–6% inhibition), whereas utilization of 4μm-d-[U−¹⁴C]glucose and ³⁵SO₄²⁻ was inhibited (41–48% and 40–59% of the control values respectively). 3. Analysis of the papain-digested glycoprotein from tissue incubations with 16·6μm-d-[2−¹⁴C]glucose in the presence of salicylate (3·75mm) showed large decreases in labelling of N-acetylneuraminic acid and N-glycollylneuraminic acid residues (57% and 34% of the control values respectively) and of hexosamine constituents (glucosamine, 55% inhibition; galactosamine, 33% inhibition). Labelling of neutral sugars (galactose and fucose) was relatively little affected (9 and 11% inhibition respectively). 4. Glucose 6-phosphate transaminase and glucosamine 6-phosphate acetylase in particle-free enzyme preparations of the sheep tissue were unaffected by salicylate at the above concentrations. Acetyl-CoA synthetase was markedly inhibited. 5. Human gastric mucosa (from operation), on incubation as above, had in one experiment an oxygen consumption of 9·9μl./hr./mg. dry wt. of tissue and incorporated 5μm-d-[U−¹⁴C]glucose (15·8% of the total radioactivity added) into bound hexosamine (20·6% of the total radioactivity incorporated), hexoses (glucose and galactose, 5·7%) and fucose (14·2%). The presence of salicylate (15mm) decreased the incorporation of 5μm-d-[U−¹⁴C]glucose into the glycoprotein by 74%, all sugar constituents being affected, without influence on the rate of oxygen consumption. 6. The results suggest an inhibitory effect of salicylate on glycoprotein biosynthesis at the level of the amino sugar intermediates.