Quantitative aspects of mucus glycoprotein biosynthesis in rat gastric mucosa

Abstract

The synthesis of the polypeptide backbone of mucus glycoproteins in rat stomach was studied. CsCl centrifugation of the homogenate of [3H]serine pulse-chase labelled stomach or mucosal scrapings showed that [3H]serine was mainly incorporated into molecules having a density identical to that of proteins and that only 8-12% was incorporated into macromolecules with the density of mucus glycoproteins. [3H]-Galactose, however, was almost exclusively incorporated into macromolecules with a density identical to that of mucus glycoproteins. Electrophoretic analysis of the CsCl fraction containing the mucus glycoprotein revealed that 78% of the [3H]serine-labelled macromolecules had an electrophoretic behaviour identical to that of mucus glycoproteins. Thus, only a small portion (about 6-10%) of incorporated [3H]serine was present in the backbone of the mucus glycoprotein. Translation in a wheat germ cell-free system of total RNA derived from both whole stomach and superficial mucosal scrapings, using either [35S]methionine or [35S]cysteine as radioactive amino acid, yielded a wide range of proteins. On sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, one major translation product of whole stomach RNA had an apparent Mr (43000) identical to that of rat pepsinogen. As this polypeptide could not be found amongst the translation products of RNA from scrapings it probably was pepsinogen. The present data provide strong evidence that the backbone polypeptide of mucus glycoproteins only accounts for a small part of the proteins synthesized by mucus-producing cells.

The Effect of Hyperglycemic Hyperinsulinemia on Small‐Intestinal Mucosal Protein Synthesis in Patients After Surgical Stress

“…In rats, it was found that sucraseisomaltase and maltase account for approximately 1% of mucosa proteins. 52 Total glycoprotein synthesis was found to be responsible for 6%-10% of total tracer incorporation in the mucosa, 53 whereas in rat liver about 10% of all proteins show a rapid turnover in the above range. 37,41 Our calculation of a size of 4% for such a rapidly turning over protein pool in human postoperative ileal mucosa would be in the range of these estimates and would, therefore, also support the validity of the rapidly turning over pool concept for explaining the enrichment changes that were seen during continuous isotope infusion over prolonged periods of time in ileal mucosa from controls.…”

Effect of Amino Acid Infusion on Human Postoperative Colon Protein Synthesis in Situ

“…According to animal data, this rapidly turning over protein pool in the gut mainly consists of enzymes or epithelial glycoproteins such as lactosaminoglycans or proteoglycans, which were found to have turnover rates in the range of 20%-30%/hour, depending on the physiologic conditions. 18 -22 Nevertheless, because the size of this specific pool amounts to Ͻ10% of the total protein pool, [23][24][25] the vast majority of proteins can still be studied in tracer infusion experiments such as ours.…”

“…18 -22 Nevertheless, because the size of this specific pool amounts to Ͻ10% of the total protein pool, [23][24][25] the vast majority of proteins can still be studied in tracer infusion experiments such as ours.…”

Biosynthesis of proteins by human gastric mucosa in vitro

“…Practical problems of studies of the structure, function and metabolism of mucous secretions have been reviewed, and lack of knowledge about the biosynthesis of the core protein of mucus, and also controversy in the understanding of the mechanism of mucus secretion, were emphasized (Carlstedt et al, 1985). Since the early work of Kent & Allen (1968), biosynthesis of gastric mucus has been investigated by a number of laboratories (Dekanski et al, 1975;Jentjens et al, 1984;Jentjens & Strous, 1985;Kent, 1972;Lukie & Forstner, 1972;Parke & Symons, 1977;Snary & Allen, 1971, 1972Spohn & McColl, 1980, 1986Starkey et al, 1974;Trotman & Greenwell, 1979;Yeomans & Millar, 1980), but so far the mechanisms involved and the fractors controlling them remain obscure. Moreover, information about the biosynthesis and secretion of mucus by human gastric mucosa is scarce.…”

“…Moreover, information about the biosynthesis and secretion of mucus by human gastric mucosa is scarce. Jentjens & Strous (1985) have formulated a hypothesis which states that the backbone polypeptide of mucus only accounts for a small part of protein synthesis of mucus-producing cells. Our evidence, based on investigations of synthesis of proteins in vitro by intact gastric mucosa and by isolated gastric epithelial-cell preparations from the guinea pig (Spohn & McColl, 1980, 1986, as also by fresh human gastric mucosa, conflicts with this hypothesis, but suggests an alternative explanation for the findings.…”