Synthesis of galactomannan sulfates

The experimental conditions for the sulfation of legume galactomannans were found, which allow for the obtainment of polysaccharides with a high degree of substitution. Sulfate esters of four galactomannans of different composition (galactose content, 16.4–47.5%) were synthesized using the SO₃-pyridine complex in dimethylformamide as a sulfating agent. The degree of substitution was as high as 1.4–1.8; it did not correlate with the content of galactose in the polysaccharides. It was found that the degree of sulfation depended on the reaction temperature in the range of 19–60°C.     

Changes to the galactose/mannose ratio in galactomannans during coffee bean (<Emphasis Type="Italic">Coffea arabica</Emphasis> L.) development: implications for in vivo modification of galactomannan synthesis

Endosperm was isolated from Arabica Caturra coffee beans 11, 15, 21, 26, 31 and 37 weeks after flowering, and the chemical composition and relative solubility of its component polysaccharides determined at each growth stage. Chemical analysis of the total mannan content of the cell wall material was done after solubilisation of galactomannans by alkaline extraction of the cell wall material followed by enzymatic digestion of the alkali-insoluble residue with a mixture of endo-mannanse and endo-glucanase. Eleven weeks after flowering, galactomannans accounted for approximately 10% of the polysaccharides but were highly substituted, with galactose/mannose ratios between 1:2 and 1:7. As the bean matured, galactomannan became the predominant polysaccharide, until 31 weeks after flowering it accounted for approximately 50% of the polysaccharides. However, it was less substituted, possessing galactose/mannose ratios between 1:7 and 1:40. Early in bean growth, up to 50% of the cell wall polysaccharides were extractable but as the galactomannan content of the bean increased there was a reduction in the extractability of all polysaccharides. The decrease in the galactose/mannose ratio of the galactomannans commenced between 21 and 26 weeks after flowering and was in synchrony with a rise in the concentration of free galactose in the beans. The results indicated that the degree of substitution of the galactomannans in coffee beans is developmentally regulated and may result, in part, from the modification of a primary synthetic product by the action of an alpha-galactosidase.     

Affinity interactions between agarose and β-1,4-glycans: a model for polysaccharide associations in algal cell walls

This paper reviews the extensive and previously unpublished work on the interactions between agarose and 1,4-linked β-d-glycans carried out at Unilever Research, Colworth Laboratory, UK. The effect of the following variables is discussed: (i) galactose content of galactomannans; (ii) substitution patterns in the agarose molecule; (iii) structural variations in the 1,4-β-d-glycan main chain; and (iv) molecular size of the 1,4-β-d-glycans.Double helices of agarose, a non-substituted regular polysaccharide comprising 1,3-linked β-d-galactose and 1,4-linked 3,6-anhydro-α-l-galactose, bind in an ordered cooperative fashion to an extended ribbon ordered conformation of sequences of 1,4-linked β-d-mannopyranose residues in plant galactomannans to give mixed gelling systems. This interaction survives, in a modified form, substitution along the agarose molecule by O-methyl ether and O-sulphate esters at O6 of the d-galactose and O2 of the 3,6-anhydro-l-galactose, and 4,6-linked pyruvic acid ketal groups on the d-galactose. The higher the level of substitution on the agarose, the weaker the interaction with galactomannan.In general, the higher the level of galactose substitution in the galactomannan the lower the extent of interaction with agarose. Evidence is presented, however, which indicates that the fine structural distribution of galactose along the galactomannan molecule is also an important determinant for the co-gelling interaction. Substituted 1,4-linked β-d-glucomannans, β-d-glucans and β-d-xylans which can form closely similar extended ribbon order conformations to the galactomannans also participate in co-gelling interactions with agarose. These β-d-glycans are similar in structure to important skeletal polysaccharides such as hemicelluloses and cellulose. This suggests that the binding between agars and β-d-glycans might mimic biological cohesion between skeleton and gel phases in natural red seaweed cell walls. The sensitivity of the interactions studied to fine details of agar and β-d-glycan structure is what might be expected on biological grounds, since the wide and subtle variations of natural polysaccharide structure are presumed to represent a mechanism for control of their intermolecular interactions.     

Structure and antioxidant activities of sulfated guar gum: homogeneous reaction using DMAP/DCC catalyst

It was essential to understand the chemical structure of polysaccharides for further research and biochemical or medical application of this natural biopolymer. In the present study, sulfated derivatives of guar gum with high degree of sulfation (DS) were synthesized using 4-dimethylaminopyridine (DMAP)/dimethylcyclohexylcarbodiimide (DCC) as catalyst in homogeneous conditions. The effects of the ratio of chlorosulfuric acid to pyridine, the content of catalyst and reaction temperature were investigated. Results of FT-IR, (1)H and (13)C NMR indicated that C-6 substitution was predominant in sulfated polysaccharide. In the sulfation reaction, a sharp decrease in M(W) was observed. The enhanced antioxidant activities of sulfated polysaccharides were not a function of a single factor but a combination of high DS and low molecule weight.     

Effect of polysaccharide structure on mechanical and thermal properties of galactomannan-based films

Films were prepared from guar gum and locust bean gum galactomannans. In addition, enzymatic modification was applied to guar gum to obtain structurally different galactomannans. Cohesive and flexible films were formed from galactomannans plasticized with 20-60% (w/w of polymer) glycerol or sorbitol. Galactomannans with lower galactose content (locust bean gum, modified guar gum) produced films with higher elongation at break and tensile strength. The mechanical properties of films were improved statistically significantly by decreasing the degree of polymerization of guar gum with mannanase treatments (4 h) of 2 and 10 nkat/g, whereas 50 nkat/g produced films with low elongation at break and tensile strength. Galactomannans with approximately 6 galactose units per 10 mannose backbone units resulted in films with 2 peaks in loss modulus spectra, whereas films from galactomannans with approximately 2 galactose groups per 10 mannose units behaved as a single phase in dynamic mechanical analysis.     

Galactomannans and a galactoglucomannan in legume seed endosperms: Structural requirements for β-mannanase hydrolysis

A series of galactomannans with varying degrees of galactose substitution have been extracted from the endosperms of legume seeds with water and alkali and the amount of substitution required for water solubility has been determined. Some were heterogeneous with respect to the degree of galactose substitution. The structural requirements for hydrolysis by plant β-mannanase have been studied using the relative rates and extents of hydrolysis of these galactomannans. A more detailed examination of the products of hydrolysis of carob galactomannan has been made. At least two contiguous anhydromannose units appear to be needed for scission. This is similar to the requirement for hydrolysis by microbial enzymes. Judas tree (Cercis siliquastrum) endosperm contained a polysaccharide with a unique composition for a legume seed reserve. Gel chromatography and electrophoresis on cellulose acetate indicated homogeneity. Hydrolysis with a mixture of β-mannanase and α-galactosidase gave a glucose-mannose disaccharide and acetolysis gave a galactose-mannose. These results, as well as the pattern of hydrolysis by β-mannanase were consistent with a galactoglucomannan structure.     

Depolymerization of legume seed galactomannan by Celloviridin G20x

The depolymerization of legume galactomannans by the commercial preparation Celloviridin G20x was studied with the aim of obtaining macromolecular fragments of a constant composition. Four galactomannans, representative of the entire range of monomer ratios characteristic of this class of phytopolysaccharides, were hydrolyzed. The galactomannans were isolated from oriental goat’s rue (Galega orientalis Lam., Man: Gal 1.1), guar (Cyamopsis tetragonoloba L., Man: Gal 1.6), honeylocust (Gleditsia triacanthos f. inermis L., Man: Gal 2.4), and sophora (Styphnolobium japonicum (L.) Schott., Man: Gal 5.1). Fragments with a monomer ratio close to that in the original polysaccharides were obtained with a high yield (75–80%). The degree of substitution of the 1,4-β-D-mannopyranose chain at position C-6 with α-galactose residues influenced the molecular weight of the final reaction product.     

Cell-Wall Carbohydrates of the Endosperm of the Seed of Gleditsia triacanthos

The endosperm of the seed of Gleditsia triacanthos L. contains 18.55% of its dry weight as nonreserve, cell-wall carbohydrates. Of this carbohydrate material, comprising mainly mannose, galactose, and glucose, 76.1% was of low-molecular weight or highly hydrophilic. Mannose, galactose, and glucose were also the major sugar components of the polysaccharides extracted with alkali (23.1% of the cell-wall), while the same sugars, with minor amounts of arabinose, form the residues. Methylation analysis of the polysaccharides and the borate-sodium hydroxide residue indicate that the cell walls are built up on a network of galactomannans, with high Man/Gal ratios, reinforced with minor amounts of cellulose.     

Pressure cell assisted solution characterization of polysaccharides. 2. Locust bean gum and tara gum

Following the work carried out on guar gum in our first paper of a series, the "pressure cell" solubilization method was applied to two other less highly substituted galactomannans: locust bean gum (LBG) and tara gum. True molecular solution of the polymers was achieved using appropriate temperature, time, and pressure regimes. The technique of capillary viscometry was used to determine the intrinsic viscosity [eta] of the "pressure cell" treated and untreated samples. Molecular weight (M(w)) and radius of gyration (R(g)) were determined by light scattering. The data obtained for LBG and tara gum were compared statistically with reliable data found for guar gum in the literature. The variation in [eta] with M(w) followed the Mark-Houwink-Sakurada relationship, giving the exponent alpha = 0.74 +/- 0.01 for galactomannans consistent with random coil behavior. The characteristic ratio, C(infinity), and the chain persistence length, L(p), were both calculated for LBG and tara gum using the Burchard-Stockmayer-Fixman (BSF) method which is appropriate for flexible to semiflexible chains. A general value of 9 < C(infinity) < 16 and 3 < L(p) < 5 nm can now be estimated with statistical confidence for all galactomannans. According to our statistical analysis, the chain persistence length was found to be insensitive to the degree of galactose substitution.     

Structural features of acetylated galactomannans from green Coffea arabica beans

Polysaccharides were extracted from green Coffea arabica beans with water (90 °C, 1 h). Galactomannans were isolated from the water extract using preparative anion-exchange chromatography. Almost all of the galactomannans eluted in two neutral populations, while almost all of the arabinogalactans bound to the column, indicating that these arabinogalactans contain charged groups. Analysis of the molecular weight distribution of the two neutral populations showed that they differ in their molecular weight. Further characterization of these neutral populations by NMR and by MALDI-TOF MS after enzymatic degradation with an endo-mannanase, showed the presence of acetyl groups linked to the galactomannans, a feature not previously described for this type of polysaccharides from coffee beans. It was found that the high molecular weight (ca. 2000 kDa) neutral fraction was highly substituted both with galactose residues and acetyl groups, while the low molecular weight (ca. 20 kDa) population was much less substituted. Based on these results it can be concluded that at least two distinctly different populations of galactomannans are present in green coffee beans. It was also shown that the degradation of the galactomannans from green coffee beans with an endo-mannanase from A. niger is hindered by the presence of acetyl groups.     

Structure-activity relationship of antithrombotic polysaccharide derivatives

Heparin has been the drug of choice in clinical pre-surgical and post-surgical prophylaxis of thrombotic events. However, because of its side-effects, such as bleeding and other disadvantages (i.e. chemical inhomogeneity and variability of its physiological activities), alternatives to heparin are an important field of research. A necessary procedure in the development of new drugs is the evaluation of structure-activity relationships. Genuine neutral polysaccharides were chemically modified and examined for their anticoagulant activities. The linear β-1,3-glucan curdlan, an easily available bacterial polysaccharide, served as the basic polymer. It could be established that the anticoagulant activity was dependent on the degree of sulfation and the molecular weight. For heparin, the sulfation pattern, i.e. the actual location of the sulfate groups along the heparin chain, was of importance in addition to the degree of sulfation. Therefore, we investigated whether there was also a relationship between the substitution pattern of the curdlan sulfates and their anticoagulant activity. For determination of the substitution pattern of the sulfated polysaccharides, a method was developed that is based on synthesis of the partially alkylated alditol acetates of the polymer and examination of these derivatives using combined gas chromatographymass spectrometry. In addition to the analytical data, the structure-activity relationship of anticoagulative curdlan sulfates is presented.     

Depolymerisation of legume seed galactomannans by Celloviridin G20x

The depolymerisation of legume seed Galactomannans by commercial preparation "Celloviridin G20x" to produce fragments of macromolecules with unchanged monomer ratio was studied. The hydrolysis of four galactomannans in whole range of monomer ratio for this phytopolysaccharide group 1.1-5.1 was performed by enzyme preparation, which is a sum of carbohydrases (producent--Trichoderma reesei). Degree of substitution 1,4-beta-D-mannopyranose chain on C-6 position by alpha-galactose residues had influence on values of molecular mass of final reaction products. The fragments with high yelds and monomer ratio nearly of that initial polysaccharides were obtained.     

On the galactosyl distribution of commercial galactomannans

A simple method was developed that enabled the enzymatic determination of the galactose distribution in galactomannans. endo-Mannanase of Aspergillus niger was used to degrade the galactomannan polymers and the degradation products were determined with high-performance anion-exchange chromatography. A whole range of commercial high-to-low substituted galactomannans was analyzed in this way. It was found that differences in the anion-exchange chromatograms reflected dissimilarities in the distribution of galactose and could be used directly to discern these dissimilarities. The differences among the various elution profiles were used to construct a similarity distance tree. In addition to this approach, the absolute amount of non-substituted mannose released by the enzyme was found to be a good discriminating factor. In this way, galactomannans with regular, blockwise, and randomly distributed galactose could be discerned. All guars and the highly substituted gum of Prosopis juliflora were found to have a blockwise distribution of galactose. For different batches of tara gum both random and blockwise distributions were found. Among batches of locust bean gum the greatest variation was observed: both random, blockwise, and ordered galactose distributions were present. Cassia gum was found to have a highly regular distribution of galactose.     

Immunological Studies on Dermatophytes I. Serological Reactivities of Neutral Polysaccharides with Rabbit Antiserum to Microsporum quinckeanum

Antiserum produced in the rabbit to autoclaved mycelial suspensions of Microsporum quinckeanum reacted with three neutral polysaccharides isolated from each of five species of dermatophytes, M. quinckeanum, Trichophyton granulosum, T. interdigitale, T. rubrum, and T. sch?nleinii. The serological reactivities of these polysaccharides, grouped as galactomannans I, galactomannans II, and glucans, were compared by qualitative precipitation analyses in gel and quantitative complement-fixation analyses. Significant differences were found among the glucans and galactomannans II but not among the galactomannans I of these species.     

Polysaccharides of cell cultures of Silene vulgaris

Callus and suspension cultures of campion (Silene vulgaris) produced pectin polysaccharides, similar in structure to the polysaccharides of intact plants. The major components of the pectins were D-galacturonic acid, galactose, arabinose, and rhamnose residues. The maximum content of pectins was found in callus. The monosaccharide composition of arabinogalactans isolated from cells and a culture medium of callus cultures were similar, with the ratio between arabinose and galactose of 1: (2.3-6.5) being retained. The arabinogalactans from the cells and culture medium of the suspension cultures also had a similar structure, and the arabinose to galactose ratio was 1: (1.5-1.8). In contrast to the callus cultures, the suspension cultures produced arabinogalactans with an increased content of arabinose residues and a decreased content of galactose residues. The greatest content of arabinogalactan was detected in the culture medium of the suspension cultures.     

不同硫取代度昆布多糖硫酸酯的合成及理化性质初步研究

目的:对昆布多糖进行不同硫取代度的硫酸酯化修饰,并对其产物的硫酸基含量、糖含量与分子量进行检测,为研究不同硫取代度昆布多糖硫酸酯的生物活性奠定物质基础。方法:采用氯磺酸-吡啶法对昆布多糖进行硫酸化修饰,通过改变硫酸化修饰条件,来制取不同硫酸基取代度的昆布多糖硫酸酯;利用盐酸水解-硫酸钡比浊法测定昆布多糖硫酸酯的硫酸基含量,并通过公式求得其硫取代度;用苯酚-硫酸法测定昆布多糖硫酸酯的多糖含量,并使用HPGPC法测定其分子量。结果:两种不同硫取代度昆布多糖硫酸酯的硫酸基含量分别为37.8%、45.92%,取代度分别为1.07、1.51,糖含量分别为44.52%、37.19%,分子量分别为13000、16000。结论:利用氯磺酸-吡啶法对昆布多糖进行硫酸酯化修饰,该方法可以获取不同取代度产物,酯化率高。     

In vivo modification of the cell wall polysaccharide galactomannan of guar transformed with a α-galactosidase gene cloned from senna

Galactomannans are composed of a 1to4 mannan backbone with varying degrees of 1to6 galactose substitutions and are found in the cell walls of legume endosperm. Like other cell wall polysaccharides, many factors controlling the metabolism of galactomannans remain to be elucidated. In the endospermous legume senna (Senna occidentalis) increased -galactosidase activity has previously been observed to coincide temporarily with a decrease of the galactose content of the galactomannan. To evaluate the potential role of -galactosidase for the control of the final galactose content, a -galactosidase gene expressed in immature senna seeds was cloned and transformed into the related high-yielding species guar (Cyamopsis tetragonoloba). The isolated cDNA encoded a 406 amino acid protein with a calculated molecular mass of 44313 Da. The amino acid sequence was 75% identical to the galactomannan hydrolysing -galactosidases from germinating guar and coffee bean. The senna -galactosidase gene was inserted behind a wheat high-molecular-weight glutenin promoter in the vector employed for transformation of guar by Agrobacterium tumefaciens-mediated gene transfer. About 30% of the guar transformants produced endosperm with galactomannans where the galactose content was significantly reduced. After self-fertilization of primary transformants displaying the highest galactose reduction of the galactomannan, endosperms of R₁ plants were analysed demonstrating that this property was inherited stably to the progeny and that it was 100% coupled to the presence of the senna -galactosidase gene. This suggests that -galactosidases can be involved in the determination of the final galactose content of endosperm galactomannans, demonstrating that cell wall polysaccharide biosynthesis can be modified in vivo.     

Tobacco transgenic lines that express fenugreek galactomannan galactosyltransferase constitutively have structurally altered galactomannans in their seed endosperm cell walls

Galactomannans [(1-->6)-alpha-D-galactose (Gal)-substituted (1-->4)-beta-D-mannans] are major cell wall storage polysaccharides in the endosperms of some seeds, notably the legumes. Their biosynthesis in developing legume seeds involves the functional interaction of two membrane-bound glycosyltransferases, mannan synthase (MS) and galactomannan galactosyltransferase (GMGT). MS catalyzes the elongation of the mannan backbone, whereas GMGT action determines the distribution and amount of Gal substitution. Fenugreek (Trigonella foenum-graecum) forms a galactomannan with a very high degree of Gal substitution (Man/Gal = 1.1), and its GMGT has been characterized. We now report that the endosperm cell walls of the tobacco (Nicotiana tabacum) seed are rich in a galactomannan with a very low degree of Gal substitution (Man/Gal about 20) and that its depositional time course is closely correlated with membrane-bound MS and GMGT activities. Furthermore, we demonstrate that seeds from transgenic tobacco lines that express fenugreek GMGT constitutively in membrane-bound form have endosperm galactomannans with increased average degrees of Gal substitution (Man/Gal about 10 in T(1) generation seeds and about 7.5 in T(2) generation seeds). Membrane-bound enzyme systems from transgenic seed endosperms form galactomannans in vitro that are more highly Gal substituted than those formed by controls under identical conditions. To our knowledge, this is the first report of structural manipulation of a plant cell wall polysaccharide in transgenic plants via a biosynthetic membrane-bound glycosyltransferase.     

Polysaccharides of green Arabica and Robusta coffee beans

Two independent procedures for the quantitative determination of the polysaccharide content of Arabica Caturra (Coffea arabica var. Caturra) and Robusta ROM (Coffea canephora var. ROM) green coffee beans showed that they both contained identical amounts of polysaccharide. Cell wall material (CWM) was prepared from the beans and partial solubilisation of component polysaccharides was effected by sequential extraction with water, 1 M KOH, 0.3% NaClO2, 4 M KOH and 8 M KOH. The monosaccharide compositions of the CWMs were similar, although Arabica beans contained slightly more mannose than Robusta. In the latter, more arabinogalactan was solubilised during preparation of the CWM and the water-soluble fraction of the CWM contained higher amounts of galactomannan than in Arabica. Linkage analysis indicated that the galactomannans possessed unbranched to branched mannose ratios between 14:1 and 30:1 which is higher than previously reported. No major difference in the structural features of the galactomannans between species was found. The arabinogalactans were heterogeneous both with regard to the degree of branching and the degree of polymerisation of their arabinan side-chains. Compared to Arabica, Robusta appeared to contain greater amounts of arabinogalactans with longer side chains. It is concluded that there was no detectable difference between the Arabica and Robusta varieties of this study in their absolute polysaccharide content or in the gross structural features of their galactomannans. Differences were apparent both in the structural features and ease of solubility of the arabinogalactans but a more detailed study of several varieties of Arabica and Robusta will be required to determine whether these differences occur consistently between species.     

A wide diversity of sulfated polysaccharides are synthesized by different species of marine sponges

Sulfated polysaccharides were extracted from four species of marine sponges by exhaustive papain digestion. These compounds were purified by anion-exchange and gel-filtration chromatography. Analysis of the purified polysaccharides revealed a species-specific variation in their chemical composition and also in their molecular masses. In the species Aplysina fulva we found a sulfated glucan with a glycogen-like structure. The other three species contained sulfated polysaccharides with variable proportions of galactose, fucose, arabinose and hexuronic acid and also with different degrees of sulfation. Although the complex nature of these polysaccharides did not allow complete structure determination, we detected the occurrence of 4-sulfated residues of fucose and arabinose in the species Dysidea fragilis. The biological role of these sulfated polysaccharides requires further investigation. They may be involved in the species-specific aggregation of sponge cells and/or in the structural integrity of sponge, resembling the proteoglycans of mammalian connective tissues.