Iodosylbenzene-Promoted Glycosylation with Selenoglycosides: Application in One-Pot Glycosylation

A novel method for the glycosylation of selenoglycosides activated by iodosylbenzene was developed. The glycosylation reaction conditions were mild, fast, and efficient, with a high tolerance to diverse protecting groups and a wide substrate scope, which is advantageous for synthesizing complex glycosides. In addition, selenoglycosides were shown to be orthogonal to thioglycosides under the promotion of iodosylbenzene. Notably, a high yield of the poorly reactive glucuronidation reaction product was obtained by acetyl-protected selenoglycoside. Finally, the orthogonal one-pot synthesis of β-(1→6) oligoglucans demonstrated the usefulness of this method in oligosaccharide synthesis.

Circumventing aglycon transfer en route to the synthesis of pentasaccharide thioglycoside donor for the chain extension of Plesiomonas shigelloides strain 302-73 (serotype O1) repeating unit

Herein we report a chemical synthesis of a pentasaccharide thioglycoside repeating unit of Plesiomonas shigelloides Strain 302-73 (Serotype O1), as a chain extension unit. In our synthetic endeavor we encountered multiple aglycon transfer reactions during glycosylations. This problem was obviated by employing a PMP group as a transient protecting group.

Activation of thioglycosides under mild alkylation conditions

Reported herein is the development of a novel method for the activation of thioglycosides and thioimidates using benzyl trichloroacetimidate in the presence of catalytic triflic acid. Excellent yields have been achieved with reactive substrates, whereas efficiency of reactions with unreactive glycosyl donors and/or acceptors was modest.

Formation of β-Configured Thioglycosides of d-Glucosamine and d-Galactosamine and Synthesis of Protected Human Milk Oligosaccharides

We report on the stereoselective multigram scale preparation of cyclohexyl- and phenyl thioglycosides of 2-azido-2-deoxy-β-d-gluco- and galactopyranosides from d-N-acetylglucosamine using a catalytic and solvent-free method. Two of the prepared building blocks were used as key intermediates for the synthesis of human milk oligosaccharides LNT and LNnT in their protected form.

Glycosyl benzoates as novel substrates for glycosynthases

The development of a procedure for the one-pot synthesis of glycosyl benzoates directly from unprotected sugars in aqueous media using 2-chloro-1,3-dimethylimidazolium chloride (DMC), thiobenzoic acid, and triethylamine is reported. These glycosyl donors are excellent substrates for wild-type and mutant glycosidases. β-Glucosyl benzoate was hydrolysed by the GH1 β-glucosidase derived from Halothermothrix orenii (HorGH1). Subsequent use of this substrate in thioligase-mediated glycosylation of p-nitrothiophenol demonstrated their superiority as donors compared to their p-nitrophenol counterparts with excellent conversions. Using a series of arene nucleophiles, we also demonstrate good to excellent conversions (up to 94%) of β-glucosyl benzoate to the corresponding p-nitrophenyl- and thioglycosides.

β-Glycosylations with 2-Deoxy-2-(2,4-dinitrobenzenesulfonyl)-amino-glucosyl/galactosyl Selenoglycosides: Assembly of Partially N-Acetylated β-(1 → 6)-Oligoglucosaminosides

An efficient protocol has been established for β-glycosylations with 2-deoxy-2-(2,4-dinitrobenzenesulfonyl)amino (2dDNsNH)-glucopyranosyl/galactopyranosyl selenoglycosides using PhSeCl/AgOTf as an activating system. The reaction features highly β-selective glycosylation with a wide range of alcohol acceptors that are either sterically hindered or poorly nucleophilic. Thioglycoside- and selenoglycoside-based alcohols prove to be viable nucleophiles, opening up new opportunities for one-pot construction of oligosaccharides. The power of this approach is highlighted by the efficient assembly of tri-, hexa-, and nonasaccharides composed of β-(1 → 6)-glucosaminosyl residues based on one-pot preparation of a triglucosaminosyl thioglycoside with DNs, phthaloyl, and 2,2,2-trichloroethoxycarbonyl as the protecting groups of amino groups. These glycans are potential antigens for developing glycoconjugate vaccines against microbial infections.

Synthesis and preliminary immunologic properties of di-/trisaccharide-conjugates related to Bacillus anthracis

Herein, the di- and trisaccharide mimics of the hexasaccharide antigen related to Bacillus anthracis were synthesized and covalently coupled with carrier proteins, such as keyhole limpet hemocyanin (KLH) and bovine serum albumin (BSA), to form the corresponding glycoconjugates 1-6. 2,3,4,6-Tetra-O-benzyl thioglycoside and 2-deoxyl-2-phthalylamino-3,4,6-tri-O-benzyl thioglycoside were applied as glycosyl donors to guarantee α or β-configuration of the newly formed glycosidic bonds. Glutaraldehyde was used as a homobifunctional cross-linker for high-efficiency coupling. The synthetic KLH-glycoconjugates 2, 4 and 6 were also used to vaccinate female Balb/c mice and the preliminary results of ELISA uncovered that all three KLH-conjugates could induce immune responses and generate oligosaccharide-specific total IgG antibodies. The trisaccharide 8, the glycosyl part of glycoconjugate 4, is of great immunogenicity.

Novel triple mutant of an extremophilic glycosyl hydrolase enables the rapid synthesis of thioglycosides

In order to expand the toolbox of enzymes available for thioglycoside synthesis, we describe here the first example of an extremophilic glycosyl hydrolase from Halothermothrix orenii (HorGH1) engineered towards thioglycosynthase activity with a novel combination of mutations. Using the triple mutant, HorGH1 M299R/E166A/E354G, a range of thioglycosides from glycosyl fluoride donors and aromatic thiols could be synthesised with exquisite stereoselectivity and good to excellent conversions (61-93%).

Synthesis of fluorinated thiodigalactoside analogues

In this work, we report the first synthesis of fluorinated thiodigalactoside analogues. We used tri-isopropylsilyl thioglycosides as masked glycosyl thiol nucleophiles for the elaboration of two monofluorinated heterodimers, one difluorinated homodimer, and one difluorinated heterodimer. Moreover, we also present an alternative synthesis of 3-deoxy-3-fluorogalactose and 4-deoxy-4-fluorogalactose from a common precursor. Finally, this small set of more stable thiodigalactoside analogues could be interesting inhibitors of galactose-specific lectins.

Phloem-Specific Methionine Recycling Fuels Polyamine Biosynthesis in a Sulfur-Dependent Manner and Promotes Flower and Seed Development

The Yang or Met Cycle is a series of reactions catalyzing the recycling of the sulfur (S) compound 5'-methylthioadenosine (MTA) to Met. MTA is produced as a by-product in ethylene, nicotianamine, and polyamine biosynthesis. Whether the Met Cycle preferentially fuels one of these pathways in a S-dependent manner remained unclear so far. We analyzed Arabidopsis (Arabidopsis thaliana) mutants with defects in the Met Cycle enzymes 5-METHYLTHIORIBOSE-1-PHOSPHATE-ISOMERASE1 (MTI1) and DEHYDRATASE-ENOLASE-PHOSPHATASE-COMPLEX1 (DEP1) under different S conditions and assayed the contribution of the Met Cycle to the regeneration of S for these pathways. Neither mti1 nor dep1 mutants could recycle MTA but showed S-dependent reproductive failure, which was accompanied by reduced levels of the polyamines putrescine, spermidine, and spermine in mutant inflorescences. Complementation experiments with external application of these three polyamines showed that only the triamine spermine could specifically rescue the S-dependent reproductive defects of the mutant plants. Furthermore, expressing gene-reporter fusions in Arabidopsis showed that MTI1 and DEP1 were mainly expressed in the vasculature of all plant parts. Phloem-specific reconstitution of Met Cycle activity in mti1 and dep1 mutant plants was sufficient to rescue their S-dependent mutant phenotypes. We conclude from these analyses that phloem-specific S recycling during periods of S starvation is essential for the biosynthesis of polyamines required for flowering and seed development.

Synthesis of a thio-linked Lewis A (Le(a)) epitope

The synthesis of heptyl (alpha-L-fucopyransoyl)-(1-->4)-S-[(beta-D-galactopyranosyl)-(1--> 3)] -1,4-dithio-beta-D-glucopyranoside (2), as thio-linked Lewis A analogue was based on thexyldimethylsilyl 3-O-allyl-2-O-benzoyl-6-O-(4-methoxybenzyl)-4-thio-beta-D-glucopyranosid e (15) which was readily obtained from D-galactose. Reaction of 15 with O-3,4-di-O-acetyl-2-O-(4-methoxybenzyl)-alpha-L-fucopyranosyl trichloroacetimidate (8) as fucosyl donor afforded the alpha-(1-->4)-thio-linked disaccharide. Replacement of the 4-methoxybenzyl groups by acetyl groups and removal of the 3a-O-allyl group afforded as 3a-O-unprotected acceptor thexyldimethylsilyl (2,3,4-tri-O-acetyl-alpha-L-fucopyranosyl)-(1-->4)-S-6-O-acetyl-2-O-benz oyl -4-thio-beta-D-glucopyranoside (19), which gave with 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl trichloroacetimidate as galactosyl donor (20) the trisaccharide. Transformation into a trichloroacetimidate as glycosyl donor, glycosylation of heptylmercaptan, and then removal of the O-acyl protective groups afforded target molecule 2.

Photoaffinity labeling of human lysosomal beta-hexosaminidase B. Identification of Glu-355 at the substrate binding site

The carbene precursor 3-azi-1-[([6-3H]-2-acetamido-2-deoxy-1-beta-D-galactopyranosyl)thi o -butane (also designated [3H]-1-ATB-GalNAc) has been used as a photoaffinity label for human lysosomal beta-hexosaminidase B (Hex B, EC 3.2.1.52) purified to apparent homogeneity from postmortal liver. [3H]-1-ATB-GalNAc behaved as an active site-directed inhibitor, which bound covalently to Hex B upon photolysis at 350 nm and resulted in 15% inactivation of enzyme activity. Up to 75% of the inactivation of Hex B was prevented by including the competitive inhibitor 2-acetamido-2-deoxy-D-glucono-1,5-lactone in the photoaffinity experiment. Incubation of [3H]-1-ATB-GalNAc with the enzyme followed by irradiation and subsequent separation of the three polypeptides composing the beta-subunit led mainly to labeling of the beta a-polypeptide. Subsequent proteolysis of beta a with trypsin and separation of the resulting peptides by high pressure liquid chromatography yielded one prominently labeled peptide fraction. Edman degradation resulted in the sequence E339ISEVFPDQFIHLGGD-EVEFK359. However, no modified amino acid was detected, indicating that the photoaffinity label was presumably bound to the peptide by a labile ester linkage. This was proven when the radiolabel was almost completely released from the peptide by treatment with aqueous ammonium hydroxide. Simultaneously, Glu-355 was converted into Gln-355, which is located within a region of Hex B that shows considerable homology with the alpha-subunit of human hexosaminidase A and other hexosaminidases from various species.

The synthesis of antibody binding-site probes: a hexasaccharide and two pentasaccharides related to the Brucella A antigen and prepared by in situ activation of thioglycosides with bromine

Two pentasaccharide analogues and a hexasaccharide fragment of the Brucella A antigen [----2)-alpha-D-Rhap4NFo-(1----]n have been prepared as their methyl glycosides. The pentasaccharide analogues each have two formamido groups replaced by hydroxyl groups. Protected derivatives of the three oligosaccharides were prepared by in situ activation with bromine of mono- and di-saccharide thioglycosides of D-rhamnose and 4-azido-4,6-dideoxy-D-mannose in the presence of a glycosyl acceptor and silver triflate as promoter. Reduction of the azido groups with hydrogen sulfide, N-formylation with ethyl formate, and hydrogenolysis then gave the target pentasaccharide glycosides.

H(+)-ATP synthase from rat liver mitochondria. A simple, rapid purification method of the functional complex and its characterization

A novel, simple, and rapid preparative method for purification of rat liver H(+)-ATP synthase by anion-exchange HPLC was developed. The H(+)-ATP synthase purified had higher ATPase activity in the absence of added phospholipids than any preparation reported previously, and this activity was completely inhibited by oligomycin. When reconstituted into proteoliposomes, the H(+)-ATP synthase showed an ATP-dependent 8-anilinonaphthalene-1-sulfonate response and ATP-Pi exchange activity, both of which were also completely inhibited by oligomycin and an uncoupler, indicating the intactness of the H(+)-ATP synthase. An immunochemical study and a labeling experiment with N,N'-[14C]dicyclohexylcarbodiimide ([14C]DCCD) demonstrated the presence of chargerin II ( a product of mitochondrial A6L DNA) and DCCD-binding protein (subunit c) in the complex. The subunits of the complex were separated into 11 main fractions by reverse-phase HPLC, and 3 of them and the delta subunit in F1 were partially sequenced. A search for sequence homologies indicated that these components were subunit b, coupling factor 6, subunit delta, and subunit epsilon. This is the first report of the existence of subunit b, factor 6, and chargerin II in H(+)-ATP synthase purified from rat liver mitochondria.

[Thioglycoside synthons for obtaining di-, tri- and hexasaccharide fragments of O-specific polysaccharides of Salmonella from serogroups A, B and D1]

The synthesis of a versatile trisaccharide synthon is described with the combination of protecting groups suitable for preparing higher oligosaccharides of the sequence Man-Rha-Gal and for introducing side-chain substituents (such as residues of 3,6-dideoxy-hexoses and alpha-D-glucose). This synthon was used for the synthesis of protected tri- and hexasaccharide fragments (as 2-phtalimidoethyl glycosides) of Salmonella polysaccharides (serological groups A, B, and D1).

Measurement of proton pump activity of the thermophilic bacterium PS3 and Nitrobacter agilis at the cytochrome oxidase level using total membrane and heptyl thioglucoside

It is possible to prepare liposomal vesicles by solubilization of total bacterial membranes with n-heptyl beta-D-thioglucoside followed by reconstitution into proteoliposomes by a freeze-thaw-sonication procedure with soybean phospholipids. The resulting proteoliposomes from total membrane fraction of sufficiently aerated cells of the thermophilic bacterium PS3 containing cytochrome aa3 showed a reasonable H+ pumping activity upon addition of reduced cytochrome c. On the other hand, the proteoliposomes reconstituted from air-limited PS3 cells containing cytochrome o and those from Nitrobacter agilis cells containing cytochrome aa3 did not show H+ pumping upon addition of reduced cytochrome c, although the vesicles showed "respiratory control"; 3-4-fold stimulation of oxygen consumption took place upon addition of an uncoupler. In proteoliposomes prepared from PS3 membranes by this method, H+-translocating ATPase (F0 X F1) was successfully reconstituted as well, suggesting that this method has wide applicability for investigation of enzymes catalyzing transmembrane processes.

The crystal structure of isopropyl 1-thio-beta-D-galactopyranoside monohydrate at 123 K

The crystal structure of isopropyl 1-thio-beta-D-galactopyranoside monohydrate is orthorhombic, P2(1)2(1)2(1), Z = 4, with cell dimensions at 123 K [293 K] of a = 7.983(1) [8.037(1)], b = 24.574(5) [24.709(4)], c = 6.329(1) [6.3736(8)] A, V = 1241.84 [1265.71] A3. The calculated and measured density is Dx = 1.371 [1.345] g cm-3, Dm = [1.340] g cm-3. Diffraction data were obtained with CuK alpha radiation and a Nonius CAD-4 diffractometer. The structure was solved by using MULTAN, and refined to R(F2) = 0.051, RW(F2) = 0.078, R(F) = 0.029, S = 1.16 for 1502 reflections. The molecule has the 4C1(D) conformation. The orientation of the primary alcohol group is gauche/trans, and that about the glycosidic C-S bond is (-)synclinal relative to the ring C-O bond. Although this compound does not form thermotropic liquid crystals, it has two crystal-to-crystal phase-transitions, at 70 and 104 degrees, prior to melting at 126 degrees. The crystal structure has a characteristic, amphiphilic, head-to-head bilayer molecular packing, with intercalated alkyl groups. The water molecule is included in the hydrogen-bond structure that links the galactoside moieties.

The crystal structure of isobutyl 2,3,4-tri-O-acetyl-1-thio-beta-D-xylopyranoside

Isobutyl 2,3,4-tri-O-acetyl-1-thio-beta-D-xylopyranoside is monoclinic, P21, with a = 10.134(4), b = 7.748(3), c = 11.726(4) A, beta = 96.63(3) degrees, V = 914.55 A3, Z = 2, Dm = 1.262, Dx = 1.264 g . cm-3, mu(MoK alpha) = 226 M-1. The X-ray intensities of 1724 reflections were measured with Nb-filtered MoK alpha radiation (lambda = 0.7107 A) at room temperature. The structure was solved by direct methods, and refined by full-matrix least squares, with anisotropic thermal parameters for the carbon and oxygen atoms and isotropic thermal parameters for the hydrogen atoms, to a final agreement factor of R = 0.08. The molecule has the 4C1(D) conformation, with puckering parameters Q = 0.582 A, theta = 5.6 degrees, phi = 334.7 degrees. The acetyl groups have the planar, (S)-cis configuration most commonly observed. They are oriented, as in many other per-O-acetylated aldopyranosides, with the acetyl planes within +/- 30 degrees of the C-H bond at the ring-carbon atom to which they are attached. Although this is primarily a van der Waals structure, there is some evidence for CH---O hydrogen-bonding.

Value of heptyl-beta-D-thioglucoside, a new nonionic detergent, in studies on membrane proteins

A new nonionic detergent, heptylthioglucoside, was synthesized and found to be more soluble than octylthioglucoside in water at low temperatures. Use of this detergent for solubilization and reconstitution of membrane proteins of Escherichia coli was examined. Heptylthioglucoside was as effective as octylthioglucoside and octylglucoside in solubilizing membrane proteins, and by the heptylthioglucoside-dilution procedure the H+-translocating ATPase (F1F0) and melibiose carrier could easily be reconstituted into liposomes. It is concluded that heptylthioglucoside is very useful in studies on membrane proteins.

Use of n-octyl-beta-D-thioglucoside, a new nonionic detergent, for solubilization and reconstitution of membrane proteins

n-Octyl-beta-D-thioglucopyranoside (octylthioglucoside), a new nonionic detergent, was synthesized. Properties of this detergent and its applicability to membrane biochemistry were investigated. The critical micelle concentration of this detergent was determined to be 9 mM. Membrane proteins of Escherichia coli were effectively solubilized with octylthioglucoside at 25-35 mM. The solubilizing power was equivalent to that of n-octyl-beta-D-glucopyranoside (octylglucoside). Reconstitution of the melibiose carrier into liposomes was performed by the detergent dilution procedure. It was found that the concentration range of octylthioglucoside for successful reconstitution (45-70 mM) was considerably wider than that of octylglucoside (43-46 mM), thus giving more reproducible results. Octylthioglucoside is more stable than octylglucoside. Furthermore, the former is synthesized with high yield at low cost whereas the latter is very expensive. Thus, we conclude that octylthioglucose is superior to octylglucoside, and is very useful in membrane biochemistry.

Conformations in solution of alpha,alpha-trehalose, alpha-D-glucopyranosyl alpha-D-mannopyranoside, and their 1-thioglycosyl analogs, and a tentative correlation of their behaviour with respect to the enzyme trehalase

The conformation in solution of alpha-D-glucopyranosyl alpha-D-glucopyranoside (alpha,alpha-trehalose, 1), alpha-D-glucopyranosyl alpha-D-mannopyranoside (3) and their corresponding 1-thioglycosyl analogs, alpha-D-glucopyranosyl 1-thio-alpha-D-glucopyranoside (1-thio-alpha,alpha-trehalose, 2) and alpha-D-glucopyranosyl 1-thio-alpha-D-mannopyranoside (4) were established from high-resolution 1H-NMR and 13C-NMR measurements. These experimental results are in good agreement with the conformations as inferred from hard-sphere calculations. The dihedral angles phi H and psi H are not significantly different for the O-glycosyl disaccharides 1 and 3 compared with their 1-thioglycosyl analogs 2 and 4; however, the internuclear H-1--H-1' and H-1--H-5' distances appear to be longer for 1-thiodisaccharides. This may account for the differences in affinities of cockchafer trehalase which have been observed. This enzyme exhibits less affinity for the competitive inhibitor alpha-D-glucopyranosyl 1-thio-alpha-D-mannopyranoside (4) than for its O-glycosyl analog 3 (Ki 0.055 mM versus 0.0057 mM). From the similarity in Ki between 1-thio-alpha, alpha-trehalose and alpha-D-glucopyranosyl 1-thio-alpha-D-mannopyranoside (0.050 mM versus 0.055 mM), it is possible to assume a similar decrease in the enzymic affinity between the natural substrate (1) and the corresponding 1-thioglycosyl inhibitor (2), which can together be ascribed to the aforementioned difference in the conformation of the molecules.

Preparation of some new neoglycoproteins by amidination of bovine serum albumin using 2-imino-2-methoxyethyl 1-thioglycosides

The cyanomethyl 1-thioglycosides of beta-D-galactose, 6-O-methyl-beta-D-galactose, alpha-L-arabinose, beta-D-fucose, beta-L-fucose, beta-D-glucose, beta-D-xylose, beta-D-allose, alpha-D-mannose, 2-acetamido-2-deoxy-beta-D-glucose, 2-acetamido-2-deoxy-beta-D-galactose, 2-deoxy-beta-D-glucose, and 3-O-methyl-beta-D-glucose were prepared from the respective pseudothiourea derivatives and chloroacetonitrile. The nitrile function in the aglycon of the cyanomethyl 1-thioglycosides was converted to a methyl imido ester by treatment with sodium methoxide in methanolic solutions, thereby affording the 2-imino-2-methoxyethyl 1-thioglycosides [Lee, Y.C., Stowell, C.P., & Krantz, M.J. (1976) Biochemistry 15, 3956-3963]. The stability of these reagents was investigated. The 2-imino-2-methoxyethyl 1-thioglycosides were then used to attach carbohydrates to bovine serum albumin. Amidination could be accomplished within a few hours in a pH range of 7-10. The extent of amidination could be controlled by varying the ratio of imido ester to protein amino group. These new neoglycoproteins were used to determine stereospecificity of the rabbit hepatic carbohydrate-binding system [Stowell, C.P., Lee, R.T., & Lee, Y.C. (1980) Biochemistry (following paper in this issue)].

beta-D-xylosidase from Penicillium wortmanni: binding and hydrolysis of alkyl and aryl 1-oxygen and 1-thio-beta-D-xylopyranosides

The influence of the chain length in n-alkyl beta-D-xylopyranosides and of the para substituents in aryl beta-D-xylopyranosides on the kinetic parameters (Ka, V) for hydrolysis of these substrates by a beta-D-xylosidase from Penicillium wortmanni, has been investigated. Binding of the corresponding 1-thio derivatives as competitive inhibitors (Ki) was studied for comparative purposes. For the n-alkyl substrates, a slight dependency of V on the chain length is noted, whereas the aryl beta-D-xylopyranosides show nearly constant V values. The influence of the aglycon on Ka and Ki values is complex; for the n-alkyl derivatives the contribution of the hydrophobicity of the aliphatic chain seems predominant, although steric factors cannot be neglected. These results, together with previous observations, can tentatively be interpreted in terms of a double-displacement mechanism.

The nutritive value of faba beans and low glucosinolate rapeseed meal for swine

Faba beans may be effectively used as a partial replacement for other protein supplements in swine diets. Breeding swine appear to be particularly sensitive to the level of faba beans in their diets. The lack of response to autoclaving faba beans suggests that the trypsin inhibitor level and condensed tannin content of faba beans do not significantly influence the performance of growing-finishing swine. Supplementation of diets containing faba beans with lysine and/or methionine has not improved pig performance. The scientific selection and commercial production of low glucosinolate varieties of rape constitutes a major advance for swine nutrition. All swine experiments that have compared low glucosinolate rapessed meal with regular rapeseed meal have demonstrated the superiority of the low glucosinolate material as a protein source. Substantially larger proportions of the low glucosinolate material may be fed to all classes of swine without any significant depression in performance.

Binding of alkyl 1-thio-beta-D-galactopyranosides to beta-D-galactosidase from E. coli

The binding of a series of alkyl 1-thio-beta-D-galactopyranosides to beta-D-galactosidase from E. coli has been investigated. The inhibition constants were compared to the partition coefficients for the transfer of these substrate-analogues from water to 1-octanol. The relationships between the observed binding-constants and the partition coefficients indicate that part of the aglycon group binds to a hydrophobic area that is limited in relation to the length of hydrocarbon chain that can be accomodated. Outside this area, the hydrocarbon chain is only partially desolvated. The main driving-force for binding of the aglycon group is the increase in entropy resulting from the return of water molecules from the more-organized layer around the solute molecule to the bulk-water phase.

2-Imino-2-methoxyethyl 1-thioglycosides: new reagents for attaching sugars to proteins

Cyanomethyl 1-thioglycosides ofD-galactose, D-glucose, 2-acetamido-2-deoxy-D-glucose, and D-mannose were prepared from the respective pseudothiourea derivatives and chloroacetonitrile. The nitrile group in these cyanomethyl thioglycosides can be converted to a methyl imidate group by treatment with sodium methoxide or HC1 in dry methanol to yield 2-imino-2-methoxyethyl 1-thioglycosides (IME-thioglycosides). The factors influencing the yield of IME-thioglycosides were investigated. The most convenient method of preparing IME-thioglycosides was treating 0.1 M cyanomethyl thioglycoside peracetate in dry methanol with 0.01 M sodium methoxide at room temperature for 24-48 h (50-60% yield). These IME-thioglycosides reacted readily with simple amines, amino acids, and proteins in mildly alkaline buffer solutions. Alpha-amylase and lysozyme modified with these reagents under appropriate conditions retained full activities. Thus the IME-thioglycosides constitute a new group of reagents for attaching sugars to proteins.

Affinity chromatography of glycosidases. Preparation and properties of affinity column adsorbents

A number of adsorbents useful for purifying glycosidases were synthesized and their adsorption and characteristics were examined using partially purified glycosidase mixtures from Takadiastase or soybean. These adsorbents were prepared by coupling di-epsilon-aminocaproyl-p-aminophenyl N-acetyl-1-thio-beta-D-glucosaminide, beta-D-glucoside, beta-D-galactoside or alpha-D-mannoside with CNBr-activated Sepharose 4B. Many glycosidases were adsorbed on the four adsorbents at low ionic strength, and increase of the ionic strength caused the enzymes to be eluted. However, the specificity of the adsorbents, contrary to our expection, was very low. All of these adsorbents adsorbed Taka N-acetyl-beta-D-glucosaminidase [EC 3.2.1.30], Taka beta-D-glucosidase [EC 3.2.1.21], and Taka beta-D-galactosidase [EC 3.2.1.23] at low ionic strength. The order of elution of these three enzymes by a linear gradient of ionic strength was the same in the four adsorbents, the order being beta-D-galactosidase, beta-D-glucosidase, and N-acetyl-beta-D-glucosaminidase. Soybean glycosidases also showed nearly the same elution pattern, though the ionic strength of the eluate was slightly lower than with Taka glycosidases. Soybean alpha-D-mannosidase [EC 3.2.1.24] was also adsorbed on these adsorbents, and was eluted between beta-D-glucosidase and N-acetyl-beta-D-glucosaminidase. These adsorption phenomena were not specific as regards the structure of the glycoside moiety, but they were useful for purifying glycosidases, possessing good reproducibility with easy activation and mild operating conditions.

Outcome of pregnancy from day 0 to 19 and serum tocopherol levels in mother rats fed on a rapeseed protein concentrate essentially free from glucosinolates

A rapeseed protein concentrate containing only minute amounts of glucosinolates was fed to rats during gestation as the sole source of protein at a 20% dietary protein level. Compared with rats obtaining a casein-based diet at the same level of protein, the mother rats on the rapeseed diet showed much lower weight gains during the last trimester. At day 19 of gestation, rats treated with rapeseed protein showed a reduced number of live fetuses and an increased resorption quotient. The average weight of the fetuses was similar, in some cases even higher, in mother rats given the rapeseed diet vis-à-vis the controls. The animals on the rapeseed diet also showed a highly significant decrease in the serum content of tocopherol, which amounted to between 24 and 41% of the control values.

Inhibition of lacZ gene translation initiation in trp-lac fusion strains

Different levels of beta-galactosidase are found in various trp-lac fusion strains. These levels of beta-galactosidase fall within a 60-fold range. The amount of thiogalactoside transacetylase activity detected in these same strains only varies 10-fold and is found in amounts greater than those predicted from the beta-galactosidase levels. The observation that the beta-galactosidase and thiogalactoside transacetylase levels are not directly proportional, that the lacZ messenger ribonucleic acid (mRNA) levels are not proportional to the beta-galactosidase activity, that, at least for the one fusion strain tested, the SuA polarity suppressor does not affect the beta-galactosidase level, and that, in all but one strain, the beta-galactosidase activity appears to reside in normal beta-galactosidase molecules suggests that the disproportionately low production of beta-galactosidase is due to a decrease in the frequency of translation initiation of lacZ mRNA in these strains. Several mechanisms are proposed to explain this decrease. Some possible bases for the disproportional production of beta-galactosidase and thiogalactoside transacetylase are also described. The preferred explanation for these disproportional enzyme levels is that only a fraction of the full complement of ribosomes need initiate translation at lacZ for the functional synthesis of lac mRNA to occur and that once the lac ribonucleic acid is made a full complement of ribosomes can bind at internal translation initiation sites at Y and A.

A mutant of Escherichia coli with a new, highly efficient promoter for the lactose operon

We have isolated a mutant of E. coli whose maximal rate of synthesis of lac mRNA is 25-fold greater than that of its parental wild-type strain. The mutant also shows alterations in the kinetics of beta-galactosidase synthesis, the functional half-life of beta-galactosidase mRNA, and the properties of lac repressor.

Solubilization and selected properties of crambe seed thioglucosidase (thioglucoside glucohydrolase, EC 3.2.3.1)

Ultrasonic treatment releases thioglucoside glucohydrolase (thioglucosidase) from insoluble particles of Crambe abyssinica seed meal. The crude enzyme is optimally activated by 10−2 M ascorbate, requires a reducing agent for stability, and is inhibited by 10−3 M p-chloromercuribenzenesulfonate.Chromatography of a meal extract on cross-linked dextran separates two enzyme fractions. About 80% of the activity elutes at an apparent molecular weight of 110 000; the remainder elutes at the void volume. Both crude soluble enzyme and the fractions from the dextran column produce goitrin from epi-progoitrin, but in the presence of ferrous ion the chief aglucon product becomes 1-cyano-2-hydroxy-3-butene. The Michaelis constant (of the major peak) at pH 5 is 0.004 M. Ferrous ion produces substrate inhibition at high epi-progoitrin levels. Sequential fractionation of meal extract by ammonium sulfate precipitation and by chromatography on cross-linked dextran effects an 80-fold purification.