Isolation and characterization of human and canine gastric mucosal glycoproteins and their degradation by proteases and acid hydrolases

High molecular weight glycoproteins were isolated and purified from canine antral and fundic mucosal tissue by means of non-degrading techniques. The results disclosed the advantage of urea extraction technique over the culture method in isolating the native glycoproteins. The glycoproteins were susceptible to degradation by protease, thus yielding low molecular weight glycopeptides. Chemical analysis of these glycopeptides and their parent macromolecules revealed that the oligosaccharide residues are attached to threonine, serine and proline residues of the protein chains. Similarly, high molecular weight glycoproteins isolated from human gastric gel mucin showed the same characteristics of canine gastric glycoproteins. Canine fundic glycoprotein or glycopeptide released their prosthetic carbohydrate groups under the lytic effect of fundic acid hydrolases.     

Glycoproteines sulfates des membranes de l'oeuf de poule et de l'oviducte Isolement et caracterisation de glycopeptides sulfatesSulfated glycoproteins form egg shell membranes and hen oviduct. Isolation and characterization of sulfated glycopeptides

Sulfated glycopeptides were isolated from pronaisc and tryptic digests of egg shell membranes and hen oviduct. They were precipitated by cationic detergents and separated by preparative electrophoresis, after removal of small quantities of glucuronoglycosaminoglycans detected only in the oviduct (isthmus and magnum). The principal isolated sulfated glycopeptides were divided according to increasing electrophoretic mobilities into two groups A and B. The homogeneity of the purified glycopeptides was confirmed by gel filtration and polyacrylamide gel electrophoresis.Glycopeptides from pool preparation of tissue are analysed and carbohydrate and amino acids average values are estimated. Hexosamines (mainly N-acetylglucosamine), hexoses (galactose, glucose, mannose) and fucose were found in Glycopeptides A. The molar ratio of hexose/hexosamine was 0.4. N-Acetylneuraminic acid and sulfate were also present in Glycopeptides A. The molar ratio of sulfate/hexosamine ranged from 0.1 to 0.25. The Glycopeptides A composition indicated the presence of chains with many glycosyl groups and a few of amino acids residues. The carbohydrate components of Glycopeptides B from egg shell membranes and magnum were found to be hexosamines (N-acetylgalactosamine and N-acetylglucosamine in equimolar proportions), hexoses (galactose mainly and glucose), N-acetylneuraminic acid, and fucose. The molar ratio of hexose/hexosamine was 1. Sulfate was also present and the molar ratio of N-acetylneuraminic acid and sulfate to hexosamine was ranged from 0.8 to 1. The main amino acid residues in these glycopeptides were serine and threonine with destruction of these hydroxyamino acids during alkali treatment. Glycopeptides B probably consist of short carbohydrate chains, linked to the polypeptide through O-glycosidic bonds involving N-acetylgalactosamine and serine and threonine. Approximately 40% of the amino acid residues were linked to carbohydrate chains.Glycopeptides B from egg shell membranes magnum and egg white were very similar in their carbohydrate and amino acid composition and in their properties.Gylcopeptides A from egg shell membranes, isthmus and magnum showed similarities and divergences especially in the amino acid composition. These results suggest that magnum and isthmus in oviduct are both concerned with the synthesis of egg shell membrane glycoproteins.     

Schistosoma mansoni synthesizes glycoproteins containing terminal O-linked N-acetylglucosamine residues

In this report, we describe our studies on the structures of the O-linked oligosaccharides in glycoproteins synthesized by the human blood fluke Schistosoma mansoni. Adult male schistosomes were incubated with either [2-3H]mannose, [6-3H]glucosamine, or [6-3H]galactose to metabolically radiolabel newly synthesized glycoproteins. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis and fluorographic analyses indicated that many glycoproteins were labeled by each of the radioactive precursors. Glycopeptides were prepared from radiolabeled glycoproteins by pronase treatment and fractionated on columns of concanavalin A-Sepharose and pea lectin-agarose. The O-linked oligosaccharides were released from glycopeptides by treatment with mild base/borohydride. All O-linked material was found in glycopeptides not bound by either of the immobilized lectins. The structures of the released chains were then analyzed by a variety of techniques. Our results demonstrate that the schistosomes synthesize glycoproteins containing two major types of simple O-linked sugar chains. One type, which represents a minor fraction of the O-linked oligosaccharides, contains N-acetylgalactosamine linked to peptide. These O-linked chains occur as terminal O-linked N-acetylgalactosamine and the O-linked disaccharide, galactose----N-acetylgalactosamine. Sialic acid was not present in either of these O-linked chains or in any other glycopeptides derived from adult male schistosomes. However, the major type of O-linked chain in glycoproteins synthesized by adult schistosomes is an unusual terminal O-linked N-acetylglucosamine linked to peptide. This latter structure represents approximately 10% of the total radioactive N-acetylglucosamine recovered in all glycopeptides. Our results also suggest the possibility that the O-linked oligosaccharides are highly clustered on the glycopeptides.     

Quantitation of the beta-elimination reaction as used on glycoproteins

The carbohydrate side chains of mucus-type glycoproteins are O-glycosidic bonds between N-acetylgalactosamine to the hydroxyl groups of serine and threonine in the protein core. The alkaline catalyzed beta-elimination reaction, in the presence of sodium borohydride, is used for determining the number of side chains. The present paper presents a study of the quantitativeness of the alkaline borohydride procedure, using four parameters: the loss of seryl and threonyl residues, the formation of alanine and 2-aminobutanoic acid; the decrease in N-acetylhexosamine and the recovery of the amino sugar alcohols. Bovine, ovine and porcine submandibular glycoproteins were studied. Evidence is presented for the existence of N-acetylglucosamine involvement in O-glycosidic linkages to serine and threonine. Results for the relative rates of beta-elimination indicate that serine-linked glycosides are released more rapidly than threonine-linked glycosides.     

Resistance to deglycosylation by ammonia of IgA1 O-glycopeptides: implications for the beta-elimination of O-glycans linked to serine and threonine

Pools of O-glycopeptides (and their deglycosylated analogues) derived from trypsin-digested normal human serum IgA1 have been treated with ammonia under conditions reported to result in complete liberation of O-glycans linked to serine and threonine residues in glycopeptides and glycoproteins. MALDI-TOF MS analysis has revealed that only one of the six glycosylated sites is susceptible to beta-elimination under these conditions. It is likely that resistance to beta-elimination is due to very close proximity of proline to the glycosylated serine or threonine residues. Preliminary results using 0.1M NaOH (instead of ammonia) to perform beta-elimination indicated that there was also selective de-O-glycosylation with this reagent, however, these results were complicated by the concomitant hydrolysis of the peptide bonds. These findings may have implications for similarly O-glycosylated peptides and proteins and possibly for other chemical methods that are used to carry out beta-eliminations of O-glycans.     

The isolation and characterization of glycopeptides and mucopolysaccharides from plasma membranes of an ascites hepatoma, AH 130.

Plasma membranes were isolated from an ascites hepatoma, AH 130, by the fluorescein mercuric acetate (FMA) method. Glycopeptides and mucopolysaccharides were prepared by digesting the membranes with pronase, then by fractionating the digest chromatographically and electrophoretically. Isolated fractions were analyzed for their amino acid and carbohydrate compositions. Results were compared with those for corresponding fractions from AH 66 (J. Biochem. 76, 319-333 (1974)). Mucopolysaccharides and a series of glycopeptides were isolated from the fraction excluded from Sephadex G-50. The mucopolysaccharides were identified as a family of heparan sulfates with different electrophoretic mobilities. The glycopeptides contained serine, threonine, galactose, galactosamine, glucosamine, and sialic acid as the major constituents as aspartic acid and mannose as minor ones. This suggests that most of the carbohydrate moieties are linked to serine or threonine (O-glycosidic), and that some are linked to asparagine (N-glycosidic). No nearly purely O-glycosidic glycopeptides were found in this fraction from AH 130, through they were the major glycopeptides from the AH 66 plasma membranes. In the fraction included in the gel, glycopeptides containing fucose, galactose, mannose, glucosamine, glaactosamine, and sialic acid were found. The presence of galactosamine suggests that some of the glycopeptides are O-glycosidic though most are N-glycosidic. In the corresponding fraction from AH 66, nearly purely N-glycosidic glycopeptides were found.     

Subcellular and anatomical distribution in rat brain of glycoproteins that contain mannose-rich heteropolysaccharide chains

Mannose-rich glycopeptides derived from brain glycoproteins were obtained by proteolysis of bovine brain tissue or subcellular fractions derived from rat brain tissue. The dialyzable mannose-rich glycopeptides were isolated by colum electrophoresis and gel flitration. These glycopeptides contained, on the average, six mannose and two N-acetylglucosamine residues with variable amounts of fucose and galactose. Over 50% of the mannose-rich glycopeptides of rat brain were localized in the microsomal and synaptosomal fractions; myelin and the soluble fraction contained lesser amounts. None was recovered from the mitochondria. The amount, per mg protein, of mannose-rich oligosaccharide chains in the myelin exceeded the concentration found in the microsomal and synaptosomal fractions. The concentration of mannose-rich glycopeptides derived from glycoproteins was 50% higher in white matter than in gray. On the other hand, the non-dialyzable and acidic sialoglycopeptides showed a three-fold enrichment in gray matter compared to white. The relatively lower ratio of sialoglycopeptides to mannose-rich glycopeptides observed in white matter (2.5) compared to gray matter (6.9) is reflected in the lower value for the ratio in myelin (1.1) compared to synpatosomes (2.1). Although glycoproteins that contain mannose-rich oligosaccharide chains are present in the nerve cell and its terminals, these glycoproteins appear to be relatively enriched in myelin and/or glial membranes.     

Relationship of the terminal sequences to the length of poly-N-acetyllactosamine chains in asparagine-linked oligosaccharides from the mouse lymphoma cell line BW5147. Immobilized tomato lectin interacts with high affinity with glycopeptides containing long poly-N-acetyllactosamine chains

To investigate the factors regulating the biosynthesis of poly-N-acetyllactosamine chains containing the repeating disaccharide [3Gal beta 1,4GlcNAc beta 1] in animal cell glycoproteins, we have examined the structures and terminal sequences of these chains in the complex-type asparagine-linked oligosaccharides from the mouse lymphoma cell line BW5147. Cells were grown in medium containing [6-3H]galactose, and radiolabeled glycopeptides were prepared and fractionated by serial lectin affinity chromatography. The glycopeptides containing the poly-N-acetyllactosamine chains in these cells were complex-type tri- and tetraantennary asparagine-linked oligosaccharides. The poly-N-acetyllactosamine chains in these glycopeptides had four different terminal sequences with the structures: I, Gal beta 1,4GlcNAc beta 1,3Gal-R; II, Gal alpha 1,3Gal beta 1,4GlcNac beta 1,3Gal-R; III, Sia alpha 2,3Gal beta 1,4GlcNAc beta 1,3Gal-R; and IV, Sia alpha 2,6Gal beta 1,4GlcNAc beta 1,3Gal-R. We have found that immobilized tomato lectin interacts with high affinity with glycopeptides containing three or more linear units of the repeating disaccharide [3Gal beta 1,4GlcNAc beta 1] and thereby allows for a separation of glycopeptides on the basis of the length of the chain. A high percentage of the long poly-N-acetyllactosamine chains bound by immobilized tomato lectin were not sialylated and contained the simple terminal sequence of Structure I. In addition, a high percentage of the sialic acid residues that were present in the long chains were linked alpha 2,3 to penultimate galactose residues (Structure III). In contrast, a high percentage of the shorter poly-N-acetyllactosamine chains not bound by the immobilized lectin were sialylated, and most of the sialic acid residues in these chains were linked alpha 2,6 to galactose (Structure IV). These results indicate that there is a relationship in these cells between poly-N-acetyllactosamine chain length and the degree and type of sialylation of these chains.     

Heterogeneity of rat goblet-cell mucin before and after reduction.

Goblet-cell mucin of rat small intestine was purified from mucosal scrapings by using centrifugation, Sepharose 4B and Sepharose 2B chromatography. The mucin was applied in low concentrations (1 microgram/track) to slab gels containing 0.5% agarose/2% (w/v) polyacrylamide, and bands were detected after electrophoresis by silver stain or by fluorography of 3H-labelled mucin. Before reduction the mucin contained three distinct components: a polymeric species at the top of the gel and two large glycoproteins of higher mobility. After reduction, the polymer disappeared, the two glycoproteins remained unchanged, and two glycopeptide bands of higher mobility appeared. In addition, a non-glycosylated, heavily stained peptide of mol.wt. 118000 was detected. The individual mucin components were partially separated on Sepharose 2B, 0.2M-NaCl/1% sodium dodecyl sulphate being used as eluant. Individual amino acid and carbohydrate analyses suggested that the glycosylated components, despite their differences in size, had identical profiles. The 118000-mol.wt. peptide had a very different amino acid profile, with much less serine, threonine and proline. Glycine and aspartic and glutamic acids comprised 34% of the total amino acids. Thus the 'native' mucin is a heterogeneous structure containing at least two non-covalently associated glycoproteins plus polymeric material. The latter is stabilized by disulphide bonds and consists of several glycopeptides of different size as well as a 'link' peptide of mol.wt. 118000.     

Glycoproteins of the opium poppy

Two carbohydrate-protein fractions were isolated from the water-soluble biopolymer from opium poppy capsules by chromatography on SP-Sephadex. The carbohydrate chains are composed of arabinose, rhamnose, xylose, mannose, glucose, galactose, galacturonic acid, glucuronic acid and 4-O-methyl glucuronic acid. Methylation analysis indicated a high degree of branching suggesting a very complex structure. Treatment of the glycoprotein with NaOH in the presence of NaBH₄ resulted in a significant decrease in the serine and threonine content. The carbohydrate side chains released contained the sugar alcohol, galactitol. These results indicate that polysaccharide chains are linked to protein via serine-O-galactoside linkages.     

Immunochemical studies on blood groups. Immunochemical properties of B-active and non-B-active blood group substances from horse gastric mucosae and the relative size distributions of oligosaccharides liberated by base-borohydride.

Horse B-active and non-B-active glycoproteins from gastric mucosae are indistinguishable in their precipitating abilities with concanavalin A, anti-BP1, type XIV horse antipneumococcal serum, the lectin from Lotus tetragonolobus and a group 1 anti-I serum, Ma; no Le^a or Le^b activity was found. Each was subjected to catalyzed release of its oligosaccharide chains by 0.05 n NaOH in 1 m NaBH₄. Destruction of serine, threonine and 2-acetamido-2-deoxygalactopyranose (dGalNAc) was associated with production of alanine, α-aminobutyric acid and N-acetyl-d-galactosaminitol, as expected for a carbohydrate to peptide linkage via dGalNAc to serine or threonine. No evidence of basecatalyzed peeling was seen. Bio-Gel P-2 elution patterns of the salt-free oligosaccharides from the two preparations were compared. Unlike results obtained with human ovarian cyst substances, very little material was excluded. The largest-size chains are in the range of deca- or dodecasaccharides, and a reduced octasaccharide was isolated. The four most abundant amino acids in both B-active and non-B-active materials are threonine, serine, proline and glutamic acid, which together account for 60% of the weight of amino acids.     

A new neuraminic acid derivative and three types of glycopeptides isolated from the Cuvierian tubules of the sea cucumber Holothuria forskali

The Cuvierian tubules of Holothuria forskali Della Chiaje, a sea cucumber found in the Adriatic Sea, were investigated with regard to their carbohydrate moieties. From a Pronase digest of these tubules three types of carbohydrate units were isolated and characterized. 1. A high-molecular-weight glycopeptide fraction was shown to contain sulphated polyfucose, galactosamine, a uronic acid and a previously unknown neuraminic acid derivative. The sulphate was shown by i.r. analysis to be present as an O-ester. The carbohydrate unit was linked O-glycosidically to threonine and serine residues in the polypeptide chain. The hitherto unknown neuraminic acid derivative (Hf-neuraminic acid) was resistant to enzymic cleavage by neuraminidase, even after mild alkaline hydrolysis for the removal of O-acyl residues. However, the glycosidic linkage of this compound to the other part of the carbohydrate moiety was readily cleaved by mild acid hydrolysis. Its chromatographic properties distinguished Hf-neuraminic acid from other known neuraminic acid derivatives (N-acetyl-, NO-diacetyl-, NOO-triacetyl- and N-glycollyl-neuraminic acid). Further, this acidic sugar was shown to possess neuraminic acid as its basic structure. Thus, an as yet unknown substituent lends the distinct properties to Hf-neuraminic acid. 2. The carbohydrate composition of a second glycopeptide fraction consisting of a derivative of neuraminic acid, galactose, mannose and glucosamine was similar to that of the well-known carbohydrate groups of the globular glycoproteins. 3. The third fraction contained two glycopeptides containing the disaccharide, glucosylgalactose, which was shown to be linked to the hydroxyl group of hydroxylysine residues of a collagen-like protein. Approximately half of these residues were glycosylated. In addition to these glycopeptides, a small amount of a third glycopeptide that carried only a galactosyl residue was detected. The amino acid sequence of the two major compounds were found to be Gly-Ala-Hyl*-Gly-Ser and Gly-Pro-Hyl*-Gly-Asp, where Hyl* represents a glycosylated amino acid residue.     

Studies on the uronic acid-containing glycoproteins of Fusarium sp. M7-1: I. Isolation and some properties of the glycoproteins.

An acidic heteropolysaccharide preparation derived from the mycelium of Fusarium sp. M7-1 was fractionated into two fractions, precipitable and nonprecipitable, by treatment with cetyltrimethylammonium bromide (Cetavlon). These two fractions were further purified to apparent homogeneity on ultracentrifugation by treatment with charcoal and gel filtration chromatographies. Two glycoproteins, precipitable GP I and nonprecipitable GP II, were obtained. The molecular weights of GP I and GP II were estimated to be about 8.8 x 10(4) and 3.7 x 10(4), respectively, on gel filtration chromatography. Both GP I and GP II contained a high proportion of serine and threonine. Treatment of GP I and GP II with alkaline solution resulted in an increase in absorbance at 240 nm. Alkaline borohydride treatment markedly decreased the number of seryl and threonyl residues and resulted in an increase in alanine and the formation of 2-aminobutyric acid. It also resulted in release of low and high molecular weight carbohydrate chains. From these results, we conclude that both GP I and GP II are glycoproteins with carbohydrate chains attached to the protein moiety through O-glycosidic linkages to the hydroxyl group of serine and/or threonine.     

Heterogeneity of protein–polysaccharides of porcine articular cartilage. The chondroitin–sulphate proteins associated with collagen

Pig articular cartilage, from which protein-polysaccharides soluble in iso-osmotic sodium acetate had been removed, was extracted in three further stages with 8m-urea in 2m-sodium acetate and with tris-HCl buffer after bacterial collagenase digestion, followed by the same urea-sodium acetate solution, thus leaving only 2% of the original uronic acid in the tissue. The histological appearance of the cartilage was unaltered until after collagenase digestion. The collagenase used did not affect the viscosity or molecular size of a protein-polysaccharide preparation obtained previously. The protein-polysaccharides in each extract differed in size, amino acid composition and protein content, but protein and keratan sulphate contents were not related to hydrodynamic size, in contrast with protein-polysaccharides extracted previously before collagenase digestion. Hydroxyproline could not be removed from those obtained by the first urea-sodium acetate extraction until degraded by heat. The galactosamine/pentose molar ratio agreed closely with the galactosamine/serine molar ratio that was destroyed on treatment with 0.5m-sodium hydroxide, showing that chondroitin sulphate was attached only to serine residues. From these molar ratios the chondroitin sulphate chains were calculated to be of the same average length in protein-polysaccharides in all three extracts although somewhat shorter than in protein-polysaccharides extracted previously. Some threonine residues were also destroyed on alkali treatment suggesting that keratan sulphate may be attached to threonine. These findings together with previous results show that differences in size, composition and physical state extend to all the protein-polysaccharides in cartilage.     

Methods for the identification of N-asparaginyl and O-seryl/threonyl glycosidic linkages to aminosugars in glycoproteins

Methods are presented for the identification of certain glycopeptide bonds in glycoproteins. Mucin-type linkages are determined following treatment of glycoproteins with alkaline sodium [³H]borohydride. Such treatment cleaves O-glycosidic bonds to serine and threonine and simultaneously labels the sugar and amino acid components of the linkage. Following acid hydrolysis and dansylation, the sugar component of the linkage is identified as its corresponding dansyl-hexosaminitol by fluorographic techniques. A method is described for the separation of dansyl-galactosaminitol and dansyl-glucosaminitol by thin-layer electrophoresis in borate buffers. The amino acid component of the glycopeptide linkage is identified by fluorography following two-dimensional thin-layer chromatography of its dansyl derivative on polyamide plates. For the analysis of plasma-type glycoproteins, glycopeptides are prepared by exhaustive pronase digestion and purified by gel filtration chromatography. Final purification is effected by dansylation and thin-layer electrophoresis. The linkage compound 2-acetamido-1-N-β-l-aspartyl-2-deoxy-β-d-glucopyranosylamine is isolated from such glycopeptides as its dansyl derivative following partial acid hydrolysis. Its identity is confirmed by comparison of its properties with those of the synthetic compound. Thus the components of the glycosylamine linkage are identified following complete acid hydrolysis, redansylation, and separation by thin-layer electrophoresis.     

Human urinary glycoproteomics; attachment site specific analysis of N- and O-linked glycosylations by CID and ECD

Urine is a complex mixture of proteins and waste products and a challenging biological fluid for biomarker discovery. Previous proteomic studies have identified more than 2800 urinary proteins but analyses aimed at unraveling glycan structures and glycosylation sites of urinary glycoproteins are lacking. Glycoproteomic characterization remains difficult because of the complexity of glycan structures found mainly on asparagine (N-linked) or serine/threonine (O-linked) residues. We have developed a glycoproteomic approach that combines efficient purification of urinary glycoproteins/glycopeptides with complementary MS-fragmentation techniques for glycopeptide analysis. Starting from clinical sample size, we eliminated interfering urinary compounds by dialysis and concentrated the purified urinary proteins by lyophilization. Sialylated urinary glycoproteins were conjugated to a solid support by hydrazide chemistry and trypsin digested. Desialylated glycopeptides, released through mild acid hydrolysis, were characterized by tandem MS experiments utilizing collision induced dissociation (CID) and electron capture dissociation fragmentation techniques. In CID-MS(2), Hex(5)HexNAc(4)-N-Asn and HexHexNAc-O-Ser/Thr were typically observed, in agreement with known N-linked biantennary complex-type and O-linked core 1-like structures, respectively. Additional glycoforms for specific N- and O-linked glycopeptides were also identified, e.g. tetra-antennary N-glycans and fucosylated core 2-like O-glycans. Subsequent CID-MS(3), of selected fragment-ions from the CID-MS(2) analysis, generated peptide specific b- and y-ions that were used for peptide identification. In total, 58 N- and 63 O-linked glycopeptides from 53 glycoproteins were characterized with respect to glycan- and peptide sequences. The combination of CID and electron capture dissociation techniques allowed for the exact identification of Ser/Thr attachment site(s) for 40 of 57 putative O-glycosylation sites. We defined 29 O-glycosylation sites which have, to our knowledge, not been previously reported. This is the first study of human urinary glycoproteins where "intact" glycopeptides were studied, i.e. the presence of glycans and their attachment sites were proven without doubt.     

Glycopeptide fractions prepared from purified central and peripheral rat myelin

Myelin was purified from rat brain and sciatic nerve after invivo labeling with [³H]fucose and [¹⁴C]glucosamine to provide a radioactive marker for glycoproteins. The glycoproteins in the isolated myelin were digested exhaustively with pronase, and glycopeptides were isolated from the digest by gel filtration on Bio-Gel P-10. The glycopeptides from brain myelin separated into large and small molecular weight fractions, whereas the glycopeptides of sciatic nerve myelin eluted as a single symmetrical peak. The large and small glycopeptide fractions from central myelin and the single glycopeptide fraction from peripheral myelin were analyzed for carbohydrate by colorimetric and gas liquid chromatographic techniques. The glycopeptides from brain myelin contained 2.4 μg of neutral sugar and 0.59 μg of sialic acid per mg total myelin protein, whereas sciatic nerve myelin glycopeptides contained 10 μg of neutral sugar and 3.8 μg of sialic acid per mg total protein. Similarly, the gas-liquid chromatographic analyses showed that the glycopeptides from peripheral myelin contained 4- to 7-fold more of each individual per mg total myelin protein than those from central myelin. Most of the sialic acid and galactose in the glycopeptides from central myelin were in the large molecular weight fraction, and the small molecular weight glycopeptides contained primarily mannose and $\text{N-}\text{acetylglucosamine}$. The considerably higher content of glycoprotein-carbohydrate in peripheral myelin supports the results of gel electrophoretic studies, which indicate that the major protein in peripheral myelin in glycosylated while the glycoproteins in purified central myelin are quantitatevely minor components.     

Structure of the cell wall proteogalactomannan from Neurospora crassa. II. Structural analysis of the polysaccharide part

The native proteoheteroglycan (PHG) from mycelia of Neurospora crassa contain two kinds of carbohydrate chains differing structure. The oligosaccharides containing mannose and galactofuranose are attached by O-glycosidic linkages to serine or threonine residues in the protein (J. Biochem. 96, 1005-1011, 1984). The second kind of carbohydrate chain is a polysaccharide containing mannose and galactofuranose as the main sugar components. The results of structural studies with methylation and NMR analyses on the native PHG and some of its specifically degraded products obtained on partial acid hydrolysis and acetolysis indicate that the polysaccharide moiety of the PHG has an (alpha 1-6) linked mannan backbone with mainly (alpha 1-2) linked side chains, each of which consists of 2 to 5 mannose units, and most of the mannosyl side chains bear beta-galactofuranosyl residues linked to the 2 positions of the mannosyl nonreducing terminals. The galactofuranose residues are linked with each other by (beta 1-5) bonds.     

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

The isolation and partial characterization of a glycoprotein isolated from individual gastric aspirates and extracts of gastric mucosae solubilized with N-acetylcysteine is described.The isolated glycoproteins and the glycoproteins from proteolysed gastric aspirates showed virtually the same carbohydrate and amino acid composition. The results indicate that they consist of a protein core to which are attached carbohydrate side-chains composed of four sugars: N-acetylgalactosamine N-acetylglucosamine, galactose, fucose showing a ratio of 1 : 3 : 4 : 2. Superimposed on this basic structure were additional sugar residues, the blood-group determinants. The results also suggest that the carbohydrate side-chains are linked by an alkali-labile O-glycosidic linkage to the threonine and serine residues of the protein core, N-acetylgalactosamine forming the link.     

Studies on Egg White Proteins

Four components of ovomucoid were digested exhaustively and four kinds of glycopeptide corresponding to the four components were separated by gel filtration. Each glycopeptide was shown to be homogenious by paper chromatography and paper electrophoresis. Molar ratios of carbohydrate components of these glycopeptides varied to some extent but the amino acid compositions of these glycopeptides were essentially identical with each other with the exception of alanine. Aspartic acid and threonine were predominant amino acids in the all glycopeptides. It is most likely that the modes of linkages between polysaccharide and protein in individual ovomucoid I, II, III and IV are essentially the same, and that the carbohydrate moiety is linked to the protein via asparaginyl residue or the hydroxyl group of threonine, although the possibility of the linkages to glutamine and serine can not be excluded.