Biosynthesis of Gastric Mucins. In Vitro Incorporation of Radioactive Glucose

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Abstract
An in vitro model for the study of the mechanism of gastric-glycoprotein (mucin) biosynthesis is described. Gastric mucosa scrapings were incubated in Eagle's minimum medium with U-14C-glucose. Linear incorporation-kinetics were observed during 4 hours. U-14C-glucose was incorporated into soluble and cell bound glycoproteins. In the acid hydrolysate of soluble and cell bound fractions all the amino acids separated by high voltage electrophoresis and all the carbohydrates separated by thin layer chromatography contained appreciable radioactivity showing the active conversion of the added radioactive glucose to all the amino acid and carbohydrate precursors used by the gastric cells for the biosynthesis of macro-molecular glycoproteins. The carbohydrate/protein ratio of the excreted glycoproteins increases steadily during the 4h incubation period suggesting that the chemical composition of the excreted mucins changes during this period. The cell bound glycoprotein fraction retains a constant composition during the 4th incubation period. The high fucose to hexose ratio of the soluble (excreted) glycoproteins suggests that they are probably identical to the gastric mucins isolated from native gastric preparation. This model is therefore considered a valid one for the study of the regulation of the biosynthesis of gastric mucins as well as for the study of drug action.