The isolation and partial characterization of a glycoprotein isolated from human gastric aspirates and from extracts of gastric mucosae

Helicobacter pylori strains vary cell shape and flagellum number to maintain robust motility in viscous environments

The helical shape of the human stomach pathogen Helicobacter pylori has been suggested to provide mechanical advantage for penetrating the viscous stomach mucus layer. Using single-cell tracking and quantitative morphology analysis, we document marked variation in cell body helical parameters and flagellum number among H. pylori strains leading to distinct and broad speed distributions in broth and viscous gastric mucin media. These distributions reflect both temporal variation in swimming speed and morphologic variation within the population. Isogenic mutants with straight-rod morphology showed 7-21% reduction in speed and a lower fraction of motile bacteria. Mutational perturbation of flagellum number revealed a 19% increase in speed with 4 versus 3 median flagellum number. Resistive force theory modeling incorporating variation of both cell shape and flagellum number predicts qualitative speed differences of 10-30% among strains. However, quantitative comparisons suggest resistive force theory underestimates the influence of cell body shape on speed for helical shaped bacteria.

Micro- and macrorheology of mucus

Mucus is a complex biological material that lubricates and protects the human lungs, gastrointestinal (GI) tract, vagina, eyes, and other moist mucosal surfaces. Mucus serves as a physical barrier against foreign particles, including toxins, pathogens, and environmental ultrafine particles, while allowing rapid passage of selected gases, ions, nutrients, and many proteins. Its selective barrier properties are precisely regulated at the biochemical level across vastly different length scales. At the macroscale, mucus behaves as a non-Newtonian gel, distinguished from classical solids and liquids by its response to shear rate and shear stress, while, at the nanoscale, it behaves as a low viscosity fluid. Advances in the rheological characterization of mucus from the macroscopic to nanoscopic levels have contributed critical understanding to mucus physiology, disease pathology, and the development of drug delivery systems designed for use at mucosal surfaces. This article reviews the biochemistry that governs mucus rheology, the macro- and microrheology of human and laboratory animal mucus, rheological techniques applied to mucus, and the importance of an improved understanding of the physical properties of mucus to advancing the field of drug and gene delivery.

The isolation and partial characterization of the major bronchial glycoproteins

Partial characterization of glycoprotein obtained from mucous secretion of the bronchi and stomach has been attempted. The isolated glycoproteins and the glycoproteins from gastric aspirates showed similar carbohydrate and amino-acid composition. They consist of a protein core to which are attached carbohydrate side chains of galactose, N-acetylglucosamine and N-acetylgalactosamine in the ratio of 4 : 3 : 1. Superimposed on this structure were additional sugar residues, the blood group determinants. The carbohydrate side chains are linked by an alkali-labile O-glycosidic linkage to the threonine and serine residues of the protein core, with N-acetylgalactosamine forming the link.

Site of synthesis, intracellular transport and secretion of glycoprotein in exocrine cells

The site of attachment of the first sugar, N-acetylgalactosamine, to the seryl and threonyl residues of the protein chain is unknown in exocrine cells. The subsequent sugars of the carbohydrate side chains, galactose and N-acetylglucosamine alternately, and the end-group sugars, galactose, N-acetylgalactosamine and fucose, are attached in the Golgi complex. Sulphate too is attached in that structure. In the stomach, sulphate is probably transferred in the most mature cisterna of the Golgi stacks, galactose and fucose in other cisternae, suggesting a gradient in transferase activities along the stack. The possibilities of regulating the amount and relative sugar composition of the glycoproteins are discussed. The secretory product is stored in granules. Their polygonal, large and swollen appearance and complex formation by loss of bordering membranes, as observed in many kinds of glycoprotein-secreting cells ('mucous cells') might be caused by ineffective fixation techniques. Direct vascular perfusion results in a picture no different from what is found in non-mucous cells. Whether secretion is merely exocytotic, as in non-mucous cells, or whether it is accompanied by a loss of membrane and even cytoplasm needs thorough investigation, with the effects of various fixation techniques being compared.

Ileal recovery of nutrients and mucin in humans fed total enteral formulas supplemented with soy fiber

The objective of this study was to determine whether soy fiber supplementation of total enteral nutrition formulas affected small intestinal recovery of nitrogen, amino acids, and carbohydrates or mucin output in eight human subjects (four males, four females) with ileostomies. The subjects ingested five test diets to provide 1.0-16.5 g soy fiber/L for 2 consecutive days each. The five test diets, each with a different soy fiber content were formulated by varying the relative proportion (1:0, 0.75:0.25, 0.5:0.5, 0.25:0.75, and 0:1) of two commercially available formulas. Effluent dry matter increased with soy fiber intake as a result of the quantitative recovery of soy fiber nonstarch polysaccharide. Nitrogen and amino acid digestibilities were unchanged by the ingestion of soy fiber. Nutrients from the total enteral nutrition formulas were well digested in the small intestine with true nitrogen and amino acid digestibilities in excess of 90% and starch digestibilities approaching 100%. Ileal mucin output was higher in male subjects and was unaffected by soy fiber intake. In summary, soy fiber supplementation does not compromise protein and carbohydrate absorption from the small intestine of humans.

Mucin-type glycoproteins

Considerable advances have been made in recent years in our understanding of the biochemistry of mucin-type glycoproteins. This class of compounds is characterized mainly by a high level of O-linked oligosaccharides. Initially, the glycoproteins were solely known as the major constituents of mucus. Recent studies have shown that mucins from the gastrointestinal tract, lungs, salivary glands, sweat glands, breast, and tumor cells are structurally related to high-molecular-weight glycoproteins, which are produced by epithelial cells as membrane proteins. During mucin synthesis, an orchestrated sequence of events results in giant molecules of Mr 4 to 6 x 10(6), which are stored in mucous granules until secretion. Once secreted, mucin forms a barrier, not only to protect the delicate epithelial cells against the extracellular environment, but also to select substances for binding and uptake by these epithelia. This review is designed to critically examine relations between structure and function of the different compounds categorized as mucin glycoproteins.

Sulphation causes heterogeneity of gastric mucins

The synthesis of mucus glycoprotein in rat stomach was studied in stomach segments, which were pulse-labelled with both [3H]galactose and [35S]sulphate and chased for various times. The radioactive glycoproteins were analyzed by CsCl centrifugation and by agarose gel electrophoresis. After a pulse-labelling for 15 min with [3H]galactose, a possible intermediate with an Mr of 200,000 and a buoyant density of 1.60 g/ml could be demonstrated. Following chase periods of 1 and 4 h, [3H]galactose and [35S]sulphate were present in glycoproteins with a mean buoyant density of 1.50 g/ml. This is clearly different from the main density of glycoproteins isolated from mucosal scrapings (1.46 g/ml). Another difference is the high electrophoretic mobility on gel electrophoretic analysis of newly synthesized glycoproteins compared to that of the major portion of the glycoproteins from mucosal scrapings. When sulphation of glycoproteins was inhibited by sodium chlorate, electrophoretic mobility and buoyant density both decreased. Sodium chlorate had no effect on glycoprotein synthesis nor on glycoprotein secretion. We conclude from our data that the heterogeneity in electrophoretic mobility and buoyant density can be attributed to a different degree of sulphation of the same glycoprotein.

The metabolism of galactose in the human gastric mucous membrane

After incubating pieces of human gastric mucous membrane with radioactive galactose, labeled metabolites of glycolysis (FDP,PEP,pyruvate):hexose and hexosamine intermediates in glycoconjugate biosynthesis (gal-1P, UDP-gal,acetylated hexosamines, and their phosphate esters), amino acids (glycine, alanine, and serine), and oxoglutarate as a metabolite of the citric acid cycle were isolated from the acid-soluble fraction. These results suggest that galactose in the human gastric mucous membrane is epimerized to glucose and metabolized in the glycolytic pathway together with oxidation in the citric acid cycle and in the direction of glycoconjugate biosynthesis.

The biosynthesis of glycoconjugates from galactose in the human gastric mucous membrane

Pieces of human gastric mucosa were incubated with labeled galactose. The ratio of glucosamine-galactosamine radioactivity in human gastric glycoconjugates, after incubation of the tissue with labeled galactose, was similar to that of the two compounds after incubation with labeled glucose.

Changes in the Incorporating Activity of 35S-Sulfate into Gastric Sulfated Glycoproteins in the Rat with Erosions by Restraint and Water Immersion Stress

The synthetic activity of rat gastric sulfated glycoproteins (SGP) in vitro was investigated at various time intervals after water immersion stress using 35S-sulfate as a precursor. More than 90 percent of the total radioactivity was incorporated into mucosal SGP, and the rest was incorporated into glycosaminoglycans in the gastric muscular layer. The incorporation of 35S-sulfate into SGP increased at 2 hr and decreased at 6 hr after the onset of stress. The incorporating activity again increased markedly at 12 hr and then recovered to the normal level at 24 hr after the onset of stress. An anti-ulcer agent, N-(N-acetyl-beta-alanyl)-L-histidine aluminum complex (AAHA), significantly increased the SGP synthetic activity at 12 hr and at 24 hr after the onset of stress. It was indicated from the elution patterns on the DEAE-cellulose column that AAHA increased the amount of highly sulfated glycoproteins compared with the stress control at 12 hr after the onset of stress. The uronic acid content in the gastric muscular layer of the rat was unchanged with stress. These results in the in vitro experiment indicate that the SGP synthetic activity does not decrease with stress load, but rather increases at 2 hr and at 12 hr after the onset of stress when a sufficient amount of 35S-sulfate is supplied. Accordingly, it is suggested that SGP facilitates the restoration of the gastric mucosal damage caused by stress.

The site of sulfated glycoprotein biosynthesis in rat gastric mucosa

The site of the synthesis of the sulfated glycoproteins in rat gastric mucosa using organ culture system has been studied. About 98% of the 35S radioactivity associated with the glycoproteins was found in corpus region. The sulfated glycoproteins were synthesized mainly in corpus, poorly in antrum and none in forestomach. The synthesized sulfated glycoproteins were heterogeneous by equilibrium centrifugation in CsCl density gradients. The 35S-labeled oligosaccharides released from the glycoproteins under alkaline condition were composed of 4-8 sugar residues.

Factors influencing the viscous properties of chicken tracheal mucins

1. Reduced viscosities, in water, of different types of mucin, such as fibrillar, gelatinous and soluble phase, separated from chicken tracheal secretions were measured. 2. H-bond breaking agents caused a significant decrease in the reduced viscosity of these mucins, but thiol-reagents alone did not have any effect. 3. Papain and Pronase did not cause any decrease in the reduced viscosity of these mucins. Neuraminidase decreased the reduced viscosity of soluble phase mucin by 50% by removing about 30% of its N-acetylneuraminic acid but had no effect on fibrillar and gelatinous mucins. Sulphatase neither removed any sulphate ester groups nor decreased the reduced viscosity. Due to some nonspecific intermolecular interaction, mixtures of mucins and enzymes or ovalbumin exhibited elevated reduced viscosities. 4. Ionic strength of the solutions appeared to decrease the reduced viscosity of these mucins. Increasing concentrations of Ca2+ in solutions of ionic strength of approx. 0.1 caused significant decrease in the reduced viscosity, but had no such effect in solutions of ionic strength of more than 0.1. 5. N-Acetylneuraminic acid and sulphate ester residues were 46.6 +/- 0.2, 43.4 +/- 0.6, 27.9 +/- 3.3 mg/g and 66.0 +/- 2.0, 34.2 +/- 3.3, 2.5 +/- 0.8 mg/g for fibrillar, gelatinous and soluble phase mucins, respectively. There appeared to be a good correlation between viscosity and N-acetylneuraminic acid contents among mucins of low reduced viscosities and between viscosity and sulphate ester residues among mucins of high reduced viscosities.

Ultrastructural visualization of galactosyl residues in various alimentary epithelial cells with the peanut lectin-horseradish peroxidase procedure

A conjugate of peanut lectin with horseradish peroxidase (PL-HRP) has been employed for ultrastructural localization of glycoprotein with presumed terminal galactose residues in mouse alimentary epithelial cells. The PL-HRP conjugate imparted electron opacity in sites that stain at the light microscopic level, as for example, Golgi cisternae in surface epithelial cells of the stomach and in superficial and deep crypt cells and goblet cells of the large intestine. Ultrastructural staining revealed that Golgi cisternae intermediate between the trans and cis faces stained selectively in these sites. Secretion stored in secretory granules or Golgi vesicles in the cells lacked affinity for PL-HRP conjugate, however. Selective staining of intermediate Golgi cisternae in cells with unreactive secretory product is interpreted as indicating the site of galactosyl transferase activity and a location where galactose occurs transitorily as the terminal sugar in the glycoprotein side chains. The luminal aspect of the surface epithelial cells in the stomach and columnar cells in the colon also stained, but with some variability. Staining of these surfaces was considered possibly attributable to PL affinity of some of the secretory glycoprotein which, after absorbing to the cell surface, lost terminal sialic acid through action of luminal enzyme. PL-HRP conjugate stained granules in pancreatic zymogen cells near the block surface but not in other cells, presumably because of limited penetration of reagent. Secretion on the surface of pancreatic acinar cells or in the lumen also exhibited affinity for PL-HRP complex as did the luminal surface of gastric chief cells. Staining of secretion in the pancreatic zymogen cells and gastric chief cells for galactose appeared inconsistent with lack of evidence for presence of glycoprotein in these sites which failed to stain with the periodic acid-Schiff or periodic acid-thiocarbohydrazide-silver proteinate methods for demonstrating glycoprotein at the light and electron microscopic levels. This discrepancy points to possible selective binding of PL-HRP conjugate to a moiety other than terminal galactose of glycoprotein in a few histologic sites. These results demonstrate the applicability of the PL-HRP technique at the ultrastructural level and provide information concerning the chemical structure of epithelial cell glycoproteins and their biosynthesis.

Ultrastructural visualization of galactose in the glycoprotein of gastric surface cells with a peanut lectin conjugate

The ultrastructural localization of peanut lectin-binding sites in the gastric surface epithelial cell has been studied using a horseradish peroxidase-labelled peanut lectin (PL-HRP) conjugate and other cytochemical techniques. The PL-HRP procedure has visualized glycoprotein with presumed terminal galactose residues in the apical plasmalemma and secreted mucins and has localized such glycoprotein selectively in the 'intermediate Golgi cisternae' situated between the saccules of the maturing face and those of the forming face of the Golgi stacks. Other cytoplasmic organelles, including the forming and stored secretory granules, did not reveal glycoprotein with terminal galactosyl residues. These results demonstrate the applicability of the PL-HRP labelling technique at the electron microscopical level to localize not only extra but also intracellular peanut lectin-reactive sites. The observation afford information concerning the possible site in the Golgi apparatus where galactose residues are added to the growing oligosaccharide side-chain of mucous glycoprotein.

Efficacy of anti-ulcer drugs on the recovery of gastric mucosal glycoproteins with aspirin-induced gastric damage in rat

The efficacy of two anti-ulcer drugs, Cimetidine and Cetraxate, on the mucus glycoproteins of gastric mucosa in the aspirin-induced gastric damage was studied in rats. Simultaneous or previous oral administration of Cimetidine or Cetraxate with aspirin reduced the diminution of the mucus glycoproteins which was occurred by aspirin administration. The recovery of the content of mucus glycoprotein in drug dosed rats occurred within 3 h after aspirin dosing and was nearly 90% of control at 5 h in all cases. Single administration of Cetraxate or Cimetidine produced an increase in the mucus glycoprotein content greater than that of the untreated control. Although a macroscopical method for the measurement of gastric damage was applied to this work, neither erosions nor linear ulcers were observed in all cases except the single administration of aspirin. The biochemical method used should be able to assess the efficacy of drugs on the mucosal lesion which cannot be expressed as the ulcer index.

Glycoprotein synthesis in the mucous cells of the vascularly perfused rat stomach. III. Mucous cells of the antrum and the duodenal glands

Labeled leucine, serine, galactose, glucosamine, fucose, and sulfate were administered to rat stomachs in a vascular perfusion system. Sections of gastric fundus and antrum, and of the duodenal glands, were studied by light-microscopic autoradiography. The rate of incorporation of radioactive label in the various mucous cell types of the antrum and of the duodenal glands was measured by counting the silver grains over each cell type and comparing this rate with that of the surface mucous cells of the fundus. The following major observations were made: The patterns of incorporation in the mucous cells on the surface and in the pits of the antrum did not differ essentially from those of the surface mucous cells of the fundus. On the contrary, the incorporation patterns of the surface mucous cells of the fundus differed considerably from those of the mucous cells of the antral glands and from the mucous cells of the duodenal glands. The mucous cells of the antral glands showed a lower incorporation rate of amino acids and of (amino) sugars, especially of galactose and glucosamine, but a higher incorporation rate of sulfate. The mucous cells of the duodenal glands showed a considerably higher rate of incorporation for serine, but a lower rate for glucosamine. No differences were seen for leucine, galactose, and sulfate. The relatively low synthetic activity of the mucous cells of antral glands correlates well with the various amounts of RER, Golgi system, and secretory granules, found in these cells, and with the histochemical staining characteristics of their mucous granules. The mucous cells of the duodenal glands are characterized by typical parallel arrays of their numerous RER cisternae and by a low number of small secretory granules.

Stimulation of mucus output from rat colon in vivo

Sodium chloride (155 mM) and N-acetyl cysteine (6 mM) were recirculated through the colons of anaesthetized rats. Mucus accumulated in the perfusion fluid which was changed at intervals to allow mucus output to be estimated by measurement of hexose. The output of mucus could be stimulated by intravenous administration of the cholinergic drugs carbachol and bethanechol; this effect was inhibited by atropine. Mucus output could also be stimulated by intravenous 5-hydroxytryptamine. This was not a muscarinic cholinergic effect because atropine did not prevent it. Neither did methysergide inhibit it; but chlorpromazine did. Precursors of 5-hydroxytryptamine, 5-hydroxytryptophan and L-tryptophan, also stimulated mucus output if given in high dosage. The results suggest that in this preparation mucus output can be stimulated by two distinct mechanisms, one cholinergic, the other involving 5-hydroxytryptamine and perhaps 5-hydroxytryptophan.

Role of galactosyl-transferases in rat gastric epithelial glycoprotein synthesis

Two galactosyl-transferases have been found in the Golgi-enriched subcellular fractions derived from rat gastric mucosa. One incorporates galactose into ovomucoid at optimal pH 6.8. The reaction can be completely inhibited by acetylglucosamine. The apparent Km for UDPgalactose is 0.024 mM. The other galactosyl-transferase incorporates galactose into desialated ovine submaxillary mucin at optimal pH 7.5 and the transfer cannot be inhibited by acetylglucosamine. The apparent Km for UDPgalactose is 0.191 mM. Both enzymes require Mn2+ and Triton X-100 for optimal galactose incorporation. The enzymes could be separated by polyacrylamide gel electrophoresis. Incorporation into endogenous glycoprotein was studied in conditions optimal for the two galactosyl-transferases: (1) at pH 6.8, using Mes as buffer system, and (2) at pH 7.5, using Tris-HCl in the presence of an inhibitory excess of acetylglucosamine. In both cases, most radioactive galactose is incorporated into macromolecules, which could be identified as epithelial glycoprotein. Endogenous incorporation in the presence of excess acetylglucosamine results in the formation of a substantial amount of a disaccharide (probably galactose-beta-(1-3)acetylgalactosamine), whereas upon incorporation at pH 6.8 almost no disaccharide is formed. Quantitative immunoprecipitation experiments with specific antibodies to the endogenous product, labelled by [3H]galactose in the presence of varying amounts of desialated ovine submaxillary mucin and/or acetylglucosamine, indicated that other galactosyl-transferases are involved in the biosynthesis of epithelial glycoprotein.

Correlation of quantitative changes of gastric mucosal glycoproteins with aspirin-induced gastric damage in rats

Quantitative changes of gastric mucosal glycoproteins with the gastric damage induced by acetylsalicylic acid (aspirin) in rat have been studied. Gastric injury was easily observed macroscopically within one hour after the oral administration of aspirin. The most striking changes occurred at five hours, and the injury was overcome within nine hours after dosing. The glycoproteins extracted from rat stomack with Tris buffer containing Triton X-100 were fractionated on Bio-Gel A-1.5 m column chromatography and divided into three fractions. The first peak, corresponding to gastric mucus macromolecular neutral and acidic glycoproteins with or without sulphate (Fr.I), was diminished after aspirin administration. A considerable alteration of Fr.I (49% of control) appeared at three hours, and a gradual return to the control value was observed subsequently. The changes in the amount of the glycoproteins were detected before the macroscopical changes of the mucosa. These results suggest that gastric ulceration induced by aspirin may be caused by a deficiency of gastric mucus macromolecular glycoproteins of gastric mucus.

Isolation and partial characterization of rat gastric mucous glycoprotein

Mucus glycoproteins from the rat stomach were characterized after their isolation from homogenates of the superficial gastric mucosa by equilibrium centrifugation in CsCl density gradients. Water-soluble as well as water-insoluble glycoproteins were studied. The latter were solubilized by 2-mercaptoethanol reduction of the homogenate. From both homogenate fractions the sames two glycoproteins 1 and 2 were purified, glycoprotein 1 being present in considerably higher amount than glycoprotein 2. Their respective buoyant densities in a CsCl gradient were 1.47--1.50 g/ml and 1.56--1.58 g/ml. The two glycoproteins expressed slight differences in gel electrophoresis and gel filtration. The results from column chromatographic comparisons between reduced and unreduced glycoproteins indicated strongly that both glycoproteins 1 and 2 were built from subunits kept together by S-S bonds. The s20,w values of the reduced glycoproteins 1 and 2 were 15.7 S and 11.6 S. Glycoprotein 1 contained 5% protein, 70% carbohydrate and 1--2% sulphate, whereas these percentages for glycoprotein 2 were 10% protein, 65% carbohydrate and 10% sulphate. The molar proportions of the main sugar components galactose, fucose, glucosamine and galactosamine were 4 :2 : 4 : 1 (glycoprotein 1) and 3 : 2 : 3 : 1 (glycoprotein 2). Blood-group activity A was expressed by glycoprotein 1, whereas glycoprotein 2 showed mainly blood-group activity Leb, some B activity and also some A activity, but to a lesser extent than glycoprotein 1.

Histochemical reactions of gastrointestinal mucosubstances with orcein, high iron diamine and Alcian blue after prior oxidation of tissue sections

The histochemical orcein reaction (orc) for mucosubstances in tissue samples from the human gastrointestinal tract was compared with PAS, high iron diamine (HID) and Alcian blue reactions at pH 1.0 or 2.5 (AB 1 and AB 2.5). Orc, HID and AB 1 reactions were performed also with prior oxidation of the tissue sections with potassium permanganate or performic acid (ox-orc, ox-HID and ox-AB reactions, respectively). Orc reaction stained mucosubstances similarly to HID and AB 1; only the brush border and goblet cells in the colon were stained. The reactions of the mucosubstances obtained with ox-orc differed from those with PAS, HID, AB 1 or AB 2.5 but were similar to those with ox-HID or ox-AB; the mucosubstances in the brush border and the goblet cells in the colon and small bowel and in the foveolar epithelium of the stomach were strongly stained. Pyloric and cardiac glands were stained faintly with ox-orc but not with ox-HID or ox-AB. Brunner's glands were negative with ox-orc, ox-HID and ox-AB reactions. It was assumed that the orc reaction stains, like HID or AB 1, sulphate groups in epithelial mucosubstances, and that sulphonic acid residues, resulting from oxidation of disulphide groups in the protein core of mucus glycoproteins, are responsible for the ox-orc as well as for the ox-HID and ox-AB reactions.

Histochemical reactions of gastrointestinal mucosubstances with high iron diamine after prior oxidation and methylation of tissue sections

High iron diamine reactions after the prior methylation and oxidation of tissue sections with performic acid or potassium permanganate (metox-HID or ox-met-HID) in epithelial mucosubstances and in mucosal mast cells were studied in tissue samples from the human gastrointestinal tract and were compared with reactions with high iron diamine without any pretreatment (HID) and high iron diamine with the prior methylation (met-HID). High iron diamine reactions after the prior oxidation (met-ox-HID, ox-met-Hid and ox-Hid) demonstrated mucosubstances in a way which seemed to operate by the staining of acidic groups evoked by the oxidation of the tissue sections. These acidic groups were not blocked by the methylation. It was supposed that they are sulphonic acids resulting from sulphur groups (sulphydryls or disulphides) in some mucus glycoproteins. Met-ox-HID and ox-met-HID reactions seemed to stain mucosubstances and mast cells in a similar way but differed from the ox-HID reactions with the manner which could be interpretated to be due to the blocking of free sulphate ester groups in reactions of the former. Met-ox-HID (and ox-met-HID) positive and in goblet cells of small and large bowel.

Glycoprotein synthesis in gastric epithelial cells of the rat. Properties of microsomal glycoprotein glycosyltransferases

1. Optimal assay conditions were determined for a microsomal glycoprotein galactosyl- and fucosyltransferase derived from gastric epithelial scrapings with both exogenous and endogenous acceptor glycoprotein. 2. Subcellular fractionation of the homogenate yielded microsomal fractions enriched in glycosyltransferases. 3. The effect of feeding on galactosyltransferase activity per cell was examined. 4. Endogenous acceptor molecules were identified as glycoproteins after labeling by means of UDP-[3H]galactose in the cell-free system.