GDP-fucose: beta-N-acetylglucosamine (Fuc to (Fuc alpha 1----6GlcNAc)-Asn-peptide)alpha 1----3-fucosyltransferase activity in honeybee (Apis mellifica) venom glands. The difucosylation of asparagine-bound N-acetylglucosamine

Incubation of honeybee (Apis mellifica) venom-gland extracts with GDP-[14C]fucose and GlcNAc beta 1----2Man alpha 1----6(GlcNAc beta 1----2Man alpha 1----3)Man beta 1----4GlcNAc beta 1----4(Fuc alpha 1----6)GlcNAc beta 1----N-Asn-peptide(NAc) gave a labeled product in 40% yield. Analysis by 500-MHz 1H-NMR spectroscopy indicated the transferred fucose-(Fuc) residue to be alpha 1----3-linked to the Asn-bound GlcNAc. Further proof was provided by one-dimensional and two-dimensional 1H-NMR analysis of the incubation mixture, after incubation with beta-N-acetylhexosaminidase. The established carbohydrate structure (formula; see text) proves the existence of a novel alpha 1----3-fucosyltransferase with the ability to effect difucosylation of the Asn-bound GlcNAc in N-glycans.     

Properties of baby-hamster kidney (BHK) cells treated with Swainsonine, an inhibitor of glycoprotein processing. Comparison with ricin-resistant BHK-cell mutants.

Baby-hamster kidney (BHK) cells were grown continuously in long-term monolayer culture in the presence of Swainsonine, an inhibitor of alpha-mannosidase II, a processing enzyme involved in glycoprotein biosynthesis. The asparagine-linked oligosaccharides (N-glycans) were isolated from Pronase-digested cells by gel filtration, ion-exchange chromatography and affinity chromatography on concanavalin A--Sepharose and lentil lectin--Sepharose. The major N-glycans, analysed by 500 MHz 1H-n.m.r. spectroscopy, were identified as hybrid structures containing five mannose residues and neutral high-mannose N-glycans. The major hybrid species contained a core-substituted fucose alpha(1----6) residue and a NeuNAc alpha(2----3)Gal beta(1----4)GlcNAc terminal sequence; smaller amounts of non-sialylated and non-fucosylated hybrid structures were also detected. Swainsonine-treated cells also produced neutral oligosaccharides containing a single reducing N-acetylglucosamine residue substituted with polymannose sequences. The glycopeptide composition of Swainsonine-treated BHK cells resembles closely that of the ricin-resistant BHK cell mutant, RicR21 [P. A. Gleeson, J. Feeney and R. C. Hughes (1985) Biochemistry 24, 493-503], except the hybrid structures of RicR21 cells contain three, not five, mannose residues. Like RicR21 cells, Swainsonine-treated BHK cells showed a greatly increased resistance to ricin cytotoxicity, but not to modeccin, another galactose-binding lectin. These effects were readily reversed on removal of Swainsonine and growth in normal medium.     

Fractionation of L-fucose-containing oligosaccharides on immobilized Aleuria aurantia lectin

The carbohydrate-binding specificity of Aleuria aurantia lectin was investigated by analyzing the behavior of a variety of fucose-containing oligosaccharides on an A. aurantia lectin-Sepharose column. Studies with complex-type oligosaccharides obtained from various glycoproteins by hydrazinolysis and their partial degradation fragments indicated that the presence of the alpha-fucosyl residue linked at the C-6 position of the proximal N-acetylglucosamine moiety is indispensable for binding to the lectin column. Binding was not affected by the structures of the outer chain moieties nor by the presence of the bisecting N-acetylglucosamine residue. These results indicated that A. aurantia lectin-Sepharose is useful for the group separation of mixtures of complex-type asparagine-linked sugar chains. Studies of glycosylated Bence Jones proteins indicated that this procedure is also applicable to intact glycoproteins. The behavior of oligosaccharides isolated from human milk and the urine of patients with fucosidosis indicated that the oligosaccharides with Fuc alpha 1----2Gal beta 1----4GlcNAc and Gal beta 1----4(Fuc alpha 1----3)GlcNAc groups interact with the lectin, but less strongly than complex-type sugar chains with a fucosylated core. Lacto-N-fucopentaitol II, which has a Gal beta 1----3(Fuc alpha 1----4)GlcNAc group, interacts less strongly than the above two groups with the matrix. Oligosaccharides with Fuc alpha 1----2Gal beta 1----3GlcNAc and Gal beta 1----4GlcNAc beta 1----3Gal beta 1----4(Fuc alpha 1----3)GlcNAc groups showed almost no interaction with the matrix.     

Ricin-resistant mutants of baby-hamster-kidney cells deficient in alpha-mannosidase-II-catalyzed processing of asparagine-linked oligosaccharides

Previous work has shown that two ricin-resistant mutants of baby hamster kidney (BHK) cells, RicR15 and RicR19, synthesize only hybrid and oligomannose-type asparagine-linked oligosaccharides [Hughes, R. C. and Mills, G. (1985) Biochem. J. 226, 487-498]. In the present report glycopeptides were released from disrupted cells by exhaustive digestion with pronase, fractionated by chromatography on concanavalin-A--Sepharose, DEAE-Sephacel and lentil-lectin--Sepharose and characterized by 500-MHz 1H-NMR spectroscopy. The major hybrid structure identified in both cell lines contains five mannose residues and the sequence NeuNAc alpha 2----3Gal beta 1----4GlcNAc beta 1----2 linked to the alpha 1----3 arm mannose of the core pentasaccharide. Analysis of extracts of normal or mutant cells has shown in the mutants a deficiency in alpha-mannosidase activity measured with p-nitrophenyl alpha-mannoside. This activity is swainsonine-sensitive and exhibits a pH optimum at about 6-6.5. Assays using a specific substrate for alpha-mannosidase II, a terminal processing glycosidase in conversion of penta-mannose hybrid intermediates to complex N-glycans, reveals a reduced activity in RicR15 cells. Analysis of glycopeptides obtained from cells labelled with [3H]fucose or [3H]galactose revealed a small proportion of branched complex N-glycans of normal structure in mutant cells.     

Carbohydrate-binding specificity of Tetracarpidium conophorum lectin.

The carbohydrate-binding specificity of a novel plant lectin isolated from the seeds of Tetracarpidium conophorum (Nigerian walnut) has been studied by quantitative hapten inhibition assays and by determining the behavior of a number of oligosaccharides and glycopeptides on lectin-Sepharose affinity columns. The Tetracarpidium lectin shows preference for simple, unbranched oligosaccharides containing a terminal Gal beta 1----4GlNAc sequence over a Gal beta 1----3GlcNAc sequence and substitution by sialic acid or fucose of the terminal galactose residue, the subterminal N-acetylglucosamine or more distally located sugar residues of oligosaccharides reduce binding activity. Branched complex-type glycans containing either Gal beta 1----4GlcNAc or Gal beta 1----3GlcNAc termini bind with higher affinity than simpler oligosaccharides. The lectin shows highest affinity for a tri-antennary glycan carrying Gal beta 1----4GlcNAc substituents on C-2 and C-4 of Man alpha 1----3 and C-2 of Man alpha 1----6 core residues. Bi- and tri-glycans lacking this branching pattern bind more weakly. Tetra-antennary glycans and mono- and di-branched hybrid-type glycans also bind weakly to the immobilized lectin. Therefore, Tetracarpidium lectin complements the binding specificities of well-known lectins such as Datura stramonium agglutinin, Phaseolus vulgaris agglutinin, and lentil lectin and will be a useful additional tool for the identification and separation of complex-type glycans.     

Characterization of the carbohydrate moiety of Clerodendron trichotomum lectins. Its structure and reactivity toward plant lectins

Lectins were isolated from fruits and leaves of Clerodendron trichotomum by affinity chromatography on lactamyl-Sepharose. The purified lectins (C. trichotomum agglutinin: CTA) were homogeneous on SDS/polyacrylamide gel electrophoresis, and the carbohydrate moiety was characterized by physicochemical and immunochemical methods. The asparagine-linked oligosaccharides were released by treatment with N-oligosaccharide glycopeptidase (almond, EC 3.5.1.52) of peptic glycopeptides obtained from fruit CTA, and separated by gel filtration and thin-layer chromatography. The structure of the predominant oligosaccharide was determined as Xyl beta 1----2 (Man alpha 1----6)(Man alpha 1----3)Man beta 1----4GlcNAc beta 1----4(Fuc alpha 1----3)GlcNAc by high-performance liquid chromatography, sugar analysis and 1H-NMR spectroscopy. The reactivity of the carbohydrate moiety of CTA toward various lectins was studied. Fruit and leaf CTAs were applied to polyacrylamide gel electrophoresis, transferred to nitrocellulose sheets and detected with horseradish-peroxidase-conjugated lectins. Concanavalin A, lentil lectin, pea lectin, Vicia faba lectin and Ulex europeus agglutinin I, but not wheat germ lectin, bound to fruit CTA. The results indicate new binding properties of these plant lectins: a beta-xylosyl residue substituted at C-2 of the beta-mannosyl residue of N-linked oligosaccharide does not affect the binding with mannose-specific lectins, lentil, pea and Vicia faba lectins can bind to N-linked oligosaccharides containing an alpha-L-fucosyl residue attached to C-3 of the asparagine-linked N-acetyl-D-glucosamine residue, and Ulex europeus agglutinin I can bind to the (alpha 1----3)-linked fucose residue of the N-linked oligosaccharide.     

Biosynthesis of Lewis fucolipid antigens in human colorectal carcinoma cells. Partial characterization of LcOse4Cer and H-1 fucolipid fucosyl transferase acceptor activities

Purified glycolipids were tested for their ability to serve as acceptors of [14C]fucose from GDP-[14C]fucose as catalyzed by cell-free extracts and purified membrane fractions of human colorectal carcinoma cells, SW1116, cultured in serum-free medium. Purified lactotetraosyl ceramide (Gal beta 1----3GlcNAc beta 1----3Gal beta 1----4Glc-Cer or LcOse4Cer) and H-1 glycolipid (Fuc alpha 1----2Gal beta 1----3GlcNAc beta 1----3Gal beta 1----4Glc-Cer or IV2 Fuc alpha LcOse4Cer) stimulated incorporation of radioactivity into lipid-soluble glycolipid at a rate greater than ten times that of Lea glycolipid [Gal beta 1----3(Fuc alpha 1----4)GlcNAc beta 1----3Gal beta 1----4Glc-Cer or III4 Fuc alpha LcOse4Cer]. The enzymatic activities in crude and purified membrane fractions were optimized for substrate concentrations (glycolipid and GDP-fucose), detergent requirement (taurocholate), pH, time and protein. The radioactive product of H-1 fucosylation migrated as discrete and distinct bands on high-performance thin-layer chromatograms (HPTLC). Evidence for their identity with Leb fucolipid described previously [Fuc alpha 1----2Gal beta 1----3(Fuc alpha 1----4)GlcNAc beta 1----3Gal beta 1----4Glc-Cer or III4IV2 (Fuc alpha) LcOse4Cer] is presented. The radioactive product of LcOse4Cer fucosylation was mainly Lea fucolipid as determined by co-migration with authentic Lea fucolipid in three HPTLC systems as native and acetylated derivatives. Our results also indicated a low level of H-1 and Leb glycolipid synthesis from LcOse4Cer. On the basis of the optima, linearity for time, and enzyme-limiting conditions, we obtained a 12-19-fold purification of the LcOse4Cer and H-1 fucosyl transferase acceptor activities in three peaks of a sucrose gradient. The peak with the highest specific activity (peak 3) was highest in density and in Na+, K+, ATPase specific activity, although NADH-cytochrome-c reductase and UDP-GalNac transferase were also present in peak 3. The apparent Km values of LcOse4Cer acceptor activity and H-1 acceptor activity in peak 3 were significantly different (p less than 0.01) by statistical tests, 2.4 microM and 0.5 microM, respectively. These apparent Km values were much lower (10(3) X) and the pH optima were lower (4.8-5.3), than the corresponding properties reported for the alpha 1----3/alpha 1----4 fucosyl transferase purified from human milk. Our results suggest a role for the non-glycosidic moieties of the acceptors and/or the tissue-specific or primitive expression of these fucosyl transferase activities.     

Structures of sugar chains of human kidney gamma-glutamyltranspeptidase

gamma-Glutamyltranspeptidase purified from human kidneys contains 4-5 asparagine-linked sugar chains in each molecule. The sugar chains were released from the polypeptide portion of the enzyme by hydrazinolysis as oligosaccharides and separated by paper electrophoresis into one neutral and two acidic fractions. By sequential exoglycosidase digestion and methylation analysis, the neutral fraction, which comprised 69% of total oligosaccharides, was shown to be a mixture of bisected bi- and triantennary complex-type sugar chains with and without a fucose on the proximal N-acetylglucosamine residue and with Gal beta 1----4GlcNAc and/or Gal beta 1----4(Fuc alpha 1----3)GlcNAc groups in their outer chain moieties. The acidic oligosaccharide fractions were mixtures of mono- and disialyl derivatives of bisected triantennary complex-type oligosaccharides with Gal beta 1----4GlcNAc and/or Gal beta 1----4(Fuc alpha 1----3)GlcNAc group in their outer chain moieties. Some of the outer chains of the acidic oligosaccharides were considered to be sialylated X-antigenic structures.     

Detection of bisected biantennary form in the asparagine-linked oligosaccharides of fibronectin isolated from human term amniotic fluid

Fibronectin purified from human term amniotic fluid contains 10 asparagine-linked sugar chains in one molecule. The sugar chains were quantitatively liberated as radioactive oligosaccharides from the polypeptide moiety by hydrazinolysis followed by N-acetylation and NaB3H4 reduction and fractionated by anion-exchange column chromatography and serial lectin affinity chromatography. The structures of these sugar chains were determined by sequential exoglycosidase digestion in combination with methylation analysis. The results indicated that they are a mixture of bisected and non-bisected bi- and triantennary complex-type sugar chains with and without a fucose on the proximal N-acetylglucosamine residue and with Gal beta 1----4GlcNAc beta 1----, GlcNAc beta 1----, Neu5Ac alpha 2----3Gal beta 1----4GlcNAc beta 1----, and Neu5Ac alpha 2----6Gal beta 1----4GlcNAc beta 1---- groups in their outer chain moieties.     

Distinct N-glycan fucosylation potentials of three lepidopteran cell lines.

The fucosyltransferase activities of three insect cell lines, MB-0503 (from Mamestra brassicae), BM-N (from Bombyx mori) and Sf-9 (from Spodoptera frugiperda), were investigated and compared with that of honeybee venom glands. Cell extracts and venom gland extracts were incubated with GDP-[14C]fucose and glycopeptides isolated from human IgG and from bovine fibrin. The labeled oligosaccharide products were released by peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase A, fluorescence marked with 2-aminopyridine and analyzed both by reversed-phase and size-fractionation HPLC. They were identified by their elution positions before and after exoglycosidase treatment in comparison with standard oligosaccharides. These experiments revealed distinct fucosylation potentials in the three cell lines tested. While MB-0503 cells, like honeybee venom glands, are able to transfer fucose into alpha 1-3 and alpha 1-6 linkage to the innermost N-acetylglucosamine, only alpha 1-6-fucosyl linkages were detected with BM-N and Sf-9 cells.     

Evidence for an O-glycan sialylation system in brain. Characterization of a beta-galactoside alpha 2,3-sialyltransferase from rat brain regulating the expression of an alpha-N-acetylgalactosaminide alpha 2,6-sialyltransferase activity

We present evidence for the existence in rat brain of several sialyltransferases able to sialylate sequentially asialofetuin. [14C]Sialylated glycans of asialofetuin were analyzed by gel filtration. Three types of [14C]sialylated glycans were synthesized: N-glycans and monosialylated and disialylated O-glycans. The varying effects of N-ethylmaleimide, lysophosphatidylcholine (lysoPtdCho) and trypsin, were helpful in the identification of these different sialyltransferases. One of them, selectively inhibited by N-ethylmaleimide, was identified as the Neu5Ac alpha 2----3Gal beta 1----3GalNAc-R:alpha 2----6 sialyltransferase previously described [Baubichon-Cortay, H., Serres-Guillaumond, M., Louisot, P. and Broquet, P. (1986) Carbohydr. Res. 149, 209-223]. This enzyme was responsible for the synthesis of disialylated O-glycans. LysoPtdCho and trypsin selectively inhibited the enzyme responsible for the synthesis of monosialylated O-glycan. N-ethylmaleimide, lysoPtdCho and trypsin did not inhibit Neu5Ac transfer onto N-glycans, giving evidence for three different molecular species. To identify the enzyme responsible for monosialylated O-glycan synthesis, we used another substrate: Gal beta 1----3GalNAc--protein obtained after galactosylation of desialylated ovine mucin by a GalNAc-R:beta 1----3 galactosyltransferase from porcine submaxillary gland. This acceptor was devoid of N-glycans and of NeuAc in alpha 2----3 linkages on the galactose residue. When using N-ethylmaleimide we obtained the synthesis of only one product, a monosialylated structure. After structural analysis by HPLC on SAX and SiNH2 columns, we identified this product as Neu5Ac alpha 2----3Gal beta 1----3GalNAc. The enzyme leading to synthesis of this monosialylated O-glycan was identified as a Gal beta 1----3GalNAc-R:alpha 2----3 sialyltransferase. When using lysoPtdCho and trypsin, sialylation was completely abolished, although the Neu5Ac alpha 2----3Gal beta 1----3GalNAc-R:alpha 2----6 sialyltransferase was not inhibited. We provided thus evidence for the interpendence between the two enzymes, the alpha 2----3 sialyltransferase regulates the alpha 2----6 sialyltransferase activity since it synthesizes the alpha 2----6 sialyltransferase substrate.     

alpha-L-fucosidase from aspergillus niger: demonstration of a novel alpha-L-(1----6)-fucosidase acting on glycopeptides

An alpha-L-fucosidase which hydrolyzes fucose from alpha-(1----6)-linkage to N-acetylglucosamine was found in Aspergillus niger. The enzyme was purified by affinity chromatography with bovine IgG glycopeptide-Sepharose 4B. The enzyme preparation released fucose from bovine IgG glycopeptide and fucosylated asialoagalactofetuin, but failed to cleave 1----2, 1----3 or 1----4 linkages of alpha-L-fucosides.     

N-acetylglucosaminyltransferase III, IV and V activities in Novikoff ascites tumour cells, mouse lymphoma cells and hen oviduct. Application of a sensitive and specific assay by use of high-performance liquid chromatography

A specific and fast method for the determination of N-acetylglucosaminyltransferase III, IV and V activity in one assay is described. The method is based on the separation by HPLC of the three transferase products formed from the common acceptor oligosaccharide substrate GlcNAc beta 1----2Man alpha 1----3(GlcNAc beta 1----2Man alpha 1---- 6)Man beta 1----4GlcNAc. Assays are not interfered with by substances that result from enzymatic or chemical breakdown of the donor substrate UDP-[14C]GlcNAc. Using this assay system N-acetylglucosaminyltransferase III, IV and V activities were estimated in Novikoff ascites tumour cells, mouse lymphoma BW 5147 cells and hen oviduct.     

Structures of the sugar chains of rabbit immunoglobulin G: occurrence of asparagine-linked sugar chains in Fab fragment

The asparagine-linked sugar chains of rabbit immunoglobulin G (IgG) and its Fc and Fab fragments were quantitatively liberated from the polypeptide portions by hydrazinolysis followed by N-acetylation and NaB3H4 reduction. After fractionation by paper electrophoresis, lectin chromatography, and gel filtration, their structures were studied by sequential exoglycosidase digestion in combination with methylation analysis. Rabbit IgG was shown to contain 2.3 mol of asparagine-linked sugar chains per molecule distributed in both the Fc and Fab fragments. The sugar chains were of the biantennary complex type containing four cores: Man alpha 1----6(Man alpha 1----3)(+/- GlcNAc beta 1----4)Man beta 1----4GlcNAc beta 1----4(+/- Fuc alpha 1----6)-GlcNAc. A total of 16 distinct neutral oligosaccharide structures was found after sialidase treatment. The galactose residue in the monogalactosylated oligosaccharides was present on either the alpha 1----3 or alpha 1----6 side of the trimannosyl core. The Fab fragments contained neutral, monosialylated, and disialylated oligosaccharides, whereas the Fc fragment contained only neutral and monosialylated structures. The oligosaccharides isolated from the Fab fragments also contained more galactose and bisecting N-acetylglucosamine residues than those from the Fc fragments.     

Peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F cannot release glycans with fucose attached alpha 1----3 to the asparagine-linked N-acetylglucosamine residue

The ability of peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F (PNGase F) from Flavobacterium meningosepticum and PNGase A from sweet almonds to deglycosylate N-glycopeptides and N-glycoproteins from plants was compared. Bromelain glycopeptide and horseradish peroxidase-C glycoprotein, which contain xylose linked beta 1----2 to beta-mannose and fucose linked alpha 1----3 to the innermost N-acetylglucosamine, were used as substrates. In contrast to PNGase A, the enzyme from F. meningosepticum did not act upon these substrates even at concentrations 100-fold higher than required for complete deglycosylation of commonly used standard substrates. After removal of alpha 1----3-linked fucose from the plant glycopeptide and glycoprotein by mild acid hydrolysis, they were readily degraded by PNGase F at moderate enzyme concentrations. Hence we conclude that alpha 1----3 fucosylation of the inner N-acetylglucosamine impedes the enzymatic action of PNGase F. Knowledge of this limitation of the deglycosylation potential of PNGase F may turn it from a pitfall into a useful experimental tool.     

PARTICULATE AND SOLUBILIZED FUCOSYL TRANSFERASES FROM MOUSE BRAIN

The transfer of [¹⁴C]fucose from GDP-[U-¹⁴C]fucose to endogenous and exogenous acceptors by particulate and solubilized preparations from mouse brain is described. Suspensions of brain microsomes incorporated [¹⁴C]fucose into a heterogenous group of glycoprotein products, which have a distribution on gel electrophoresis similar to those synthesized in vivo. Fucosyl transferase, extracted from brain microsomes by Triton X-100, transferred [¹⁴C]fucose from GDP-[U-¹⁴C]fucose to terminal galactose residues exposed by mild acid hydrolysis of porcine plasma glycoprotein. Comparison of the specific activities of the solubilized fucosyl transferase from a number of organs showed that, in the presence of the exogenous acceptor which was used, the transferase of brain was more active than the transferases from all other organs tested, with the exception of kidney. Examination of subcellular fractions of brain, with endogenous and exogenous acceptors, showed that activity was limited to fractions containing microsomal membranes, whereas synaptosomal and other fractions were virtually inactive.     

The function of beta-N-acetyl-D-glucosaminyl monophosphorylundecaprenol in biosynthesis of lipoteichoic acids in a group of Bacillus strains

Membrane preparations, obtained from Bacillus strains which have N-acetylglucosamine-linked lipoteichoic acids in their membranes, were shown to catalyze the transfer of N-[14C]acetylglucosamine (GlcNAc) from beta-[14C]GlcNAc-P-undecaprenol to endogenous polymer. In this reaction, alpha-GlcNAc-P-undecaprenol or alpha-GlcNAc-PP-undecaprenol could not substitute for beta-GlcNAc-P-undecaprenol as the N-acetylglucosamine donor. This enzyme was most active at pH 6.0 and in the presence of 40 mM MgCl2. The apparent Km for beta-GlcNAc-P-undecaprenol was 2 microM. The radioactive polymer products, solubilized by hot phenol treatment, coincided with lipoteichoic acids in chromatographic behavior. Hydrogen fluoride treatment of the polymer products gave a major fragment identical with GlcNAc(alpha 1----2)glycerol, which corresponded to the dephosphorylated repeating units of the lipoteichoic acids in the examined strains. Thus it is concluded that beta-GlcNAc-P-undecaprenol serves as the donor of N-acetylglucosamine in the biosynthesis of lipoteichoic acids in a group of Bacillus strains.     

Solubilization and properties of GDP-fucose: xyloglucan 1,2-alpha-L-fucosyltransferase from pea epicotyl membranes

GDP-fucose:xyloglucan 1,2-alpha-L-fucosyltransferase from pea (Pisum sativum) epicotyl microsomal membranes was readily solubilized by extraction with the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (Chaps). When using GDP-[14C]fucose as fucosyl donor and tamarind xyloglucan (XG) as acceptor, maximum activation was observed at 0.3% (w/v) Chaps and the highest yield of solubilized activity at 0.4%. The reaction product was hydrolyzed by Trichoderma cellulase to yield labeled oligosaccharides that peaked on gel permeation chromatography at the same elution volume as pea XG nona- and decasaccharide subunits. The apparent Km for fucosyl transfer to tamarind XG by the membrane-bound or solubilized enzyme was about 80 microM GDP-fucose. This was 10 times the apparent Km for fucosyl transfer to endogenous pea nascent XG. Optimum activity was between pH 6 and 7, and the isoelectric point was close to pH 4.8. The solubilized enzyme showed no requirement for, or stimulation by, added cations or phospholipids, and was stable for several months at -70 degrees C. Solubilization and gel permeation chromatography on columns of Sepharose CL-6B enriched the specific activity of the enzyme by about 20-fold relative to microsomes. Activity fractionated on columns of CL-6B with an apparent molecular weight of 150 kDa. The solubilized fucosyltransferase was electrophoresed on nondenaturing polyacrylamide slab gels containing 0.02% (w/v) tamarind XG, and its activity located by incubation in GDP-[14C]fucose, washing, and autoradiographing the gel. A single band of labeled reaction product appeared with an apparent molecular weight of 150 kDa.     

Biosynthesis of glycoproteins by membranes of Acer pseudoplatanus. Incorporation of mannose and N-acetylglucosamine.

Membrane preparations from Acer pseudoplatanus suspension cultures were demonstrated to incorporate radioactivity from GDP-[U-14C]mannose and UDP-N-acetyl-[6-(3)H]glucosamine into high-molecular-weight polymers characterized as glycoprotein. From 20 to 25% of the 14C was incorporated as fucose with the remainder as mannose, whereas 90% of the 3H was incorporated as N-acetylglucosamine with the remainder as N-acetylgalactosamine. Pronase digestion yielded radioactive glycopeptides that were separated into four fractions by gel-permeation chromatography and paper electrophoresis. The isolated glycopeptides differed in molecular weight and isotopes incorporated, as well as in amino-acid and monosaccharide composition. The membrane preparation also incorporated radioactivity from the added nucleotides into chloroform/methanol (2:1, v/v)- and chloroform/methanol/water (10:10:3, by vol.)-soluble lipids, and into an insoluble pellet.     

Structures of the sugar chains of mouse immunoglobulin G

The asparagine-linked sugar chains of mouse immunoglobulin G (IgG) were quantitatively liberated as radioactive oligosaccharides from the polypeptide portions by hydrazinolysis followed by N-acetylation, and NaB3H4 reduction. After fractionation by paper electrophoresis, lectin (RCA120) affinity high-performance liquid chromatography, and gel filtration, their structures were studied by sequential exoglycosidase digestion in combination with methylation analysis. Mouse IgG was shown to contain the biantennary complex type sugar chains. Eight neutral oligosaccharide structures, viz, +/- Gal beta 1----4GlcNAc beta 1----2Man alpha 1----6(+/- Gal beta 1---- 4GlcNAc beta 1----2Man alpha 1----3)Man beta 1----4GlcNAc beta 1----4(+/- Fuc alpha 1----6)GlcNAc, were found after the sialidase treatment. The molar ratio of the sugar chains with 2,1, and 0 galactose residues was 2:5:3. The galactose residue in the monogalactosylated sugar chains was distributed on Man alpha 1----3 and Man alpha 1----6 sides in the ratio of 1:3. The oligosaccharides were almost wholly fucosylated and contained no bisecting N-acetylglucosamine which is present in human, rabbit, and bovine IgGs.