Analytical and structural features of the gum exudate from Combretum hartmannianum schweinf.

The gum exudate from Combretum hartmannianum is water-soluble, forms very viscous solutions, and contains galactose (22%), arabinose (43%), mannose (10%), xylose (6%), rhamnose (4%), glucuronic acid (6%), 4-O-methylglucuronic acid (2%), and galacturonic acid (7%). The acidic components produced on hydrolysis of the gum were 6-O-(β-D-glucopyranosyluronic acid)-D-galactose, and two saccharides that had the same chromatographic mobility, and contained mannose and galacturonic acid, and galactose and 4-O-methylglucuronic acid, respectively. Methylation and methanolysis of the gum indicated the presence of terminal uronic acid, rhamnose, xylose, galactose, arabinofuranose, and arabinopyranose. Controlled, acid hydrolysis indicated the presence of (1→3)-linked arabinopyranose side-chains and (1→6)-linked galactose residues. C. hartmannianum gum, when subjected to two Smith-degradations, yielded Polysaccharides I and II, both of which contained galactose, arabinose, and mannose. Insufficient crude gum was available for a complete structural study, but the molecule was shown to contain long, sparsely branched chains of (1→6)-linked galactose residues, to which are attached (1→3)-linked arabinose and (1→3)-linked mannose side-chains.     

The extracellular polysaccharides of Rhizobium japonicum: Compositional studies

The extracellular polysaccharides of seven strains of Rhizobium japonicum were investigated by using a gas-chromatographic scheme developed for determination of the various sugars present. These polysaccharides were more heterogeneous in their composition than those of any other species of Rhizobium yet examined. Five strains (1809, 110, 123, 127, and 709) produced polysaccharides containing the same constituents, although in varying relative amounts: glucose (36–44%), galactose (7–25%), mannose (18–20%), 4-O-methylgalactose (5–13%), galacturonic acid (12–16%), and acetyl groups (4–8%). The sugars of the polysaccharide of strain 1809 were all of the d series. These are the first bacterial polysaccharides reported to contain 4-O-methylgalactose and the first Rhizobium polysaccharides in which galacturonic acid has been found. In contrast to this, the polysaccharide of strain 129 consisted of glucose (7%), galactose (51%), mannose (5%), xylose (5%), glucuronic acid (5%), and pyruvic acid (2%). The polysaccharide of strain 711 contained glucose (34%), galactose (13%), mannose (27%), and pyruvic acid (6%).     

Gum arabic glycoprotein is a twisted hairy rope : a new model based on o-galactosylhydroxyproline as the polysaccharide attachment site

Separation of the wound exudate from Acacia senegal (L.) Willd., “gum arabic,” on a preparative Superose-6 column gave two major fractions: a high molecular weight gum arabic glycoprotein (GAGP) containing about 90% carbohydrate and a lower molecular weight heterogenous gum arabic polysaccharide fraction. Hydrogen fluoride-deglycosylation of GAGP gave a large (~400 residue) hydroxyproline-rich polypeptide backbone (dGAGP). Alkaline hydrolysis of GAGP showed that most of the carbohydrate was attached to the polypeptide backbone as small (~30 residue) hydroxyproline (Hyp)-polysaccharide substituents. After partial acid hydrolysis of the Hyp-polysaccharide fraction we identified O-galactosylhydroxyproline as the glycopeptide linkage, identical with that of hydroxyproline-rich arabinogalactan-proteins (AGPs). However, unlike the acidic alanine-rich AGPs, GAGP is basic and notably deficient in alanine. Thus, while the GAGP polypeptide backbone more closely resembles that of the Hyp-rich cell wall protein extensin, the GAGP polysaccharide sidechains resemble AGPs. Possibly all three proteins comprise a phylogenetically related extensin superfamily of extended rod-like macromolecules. The “wattle-blossom” model for AGP and gum arabic predicts a few large polysaccharide substituents along the polypeptide backbone of a spheroidal macromolecule. On the contrary, our data imply a rodlike molecule with numerous small polysaccharide substituents (attached to 24% of the Hyp residues), regularly arranged along a highly periodic polypeptide backbone based, hypothetically, on a 10 to 12 residue repetitive peptide motif. Thus, a simple statistical model of the gum arabic glycoprotein predicts a repeating polysaccharide-peptide subunit of about 7 kilodaltons. The small polysaccharide substituents will maximize intramolecular hydrogen bonding if aligned along the long axis of the molecule, forming in effect a twisted hairy rope. Electron micrographs of rotary shadowed GAGP molecules support that prediction and may also explain how such apparently large molecules can exit the cell by endwise reptation through the small pores of the primary cell wall.     

Structural study of the extracellular polysaccharide gum from Rhizobium strain CB744

The structure of the extracellular polysaccharide gum from nitrogen-fixing Rhizobium sp. strain CB744 (a member of the slow-growing Cowpea group) has been investigated. Gas-chromatographic analysis of the alditol acetates of the acid hydrolysate showed the gum to be composed of galactose, 4-O-methylgalactose, mannose, and glucose in the molar ratio of 1:2.5:3.5:7.0. The polysaccharide is unusual in that it contains no carbonyl substituent, although such substituents are common amongst polysaccharides produced by the slow-growing group. The native and de-branched polysaccharides were examined by methylation analysis. The anomeric configurations were determined by ¹³C-n.m.r. and oxidation by chromium trioxide. It is concluded that there are two β-(1→4)-linked glycopyranosyl residues for each α-(1→4)-linked mannopyranosyl residue, and that each mannose is substituted at O-6 by a β-galactopyranosyl residue, with 71% of the galactose groups being present as 4-O-methylgalactose.     

Composition of gum exudates from Anacardium occidentale

The composition and solution properties of Indian and Papuan specimens of the gum from Anacardium occidentale have been studied and found to be closely similar. Contrary to earlier reports by Indian workers, this gum does not contain galacturonic acid. It does, however, contain glucose; this appears to be the first report of the presence of this sugar in a plant gum exudate. A freeze-dried sample of the gum was examined at intervals over a period of 2 months; its weight-average MW increased by a factor of three in that time, and molecular-sieve chromatography showed that self-association occurred with the formation of a small proportion of a very high MW component.     

The gum exudates from Brachystegia and Julbernardia species

Analytical data are presented for the water-soluble gum exudates from Brachystegia glaucescens, B. spiciformis, and Julbernardia globiflora. They are acidic polysaccharides containing glucuronic acid, 4-O-methylglucuronic acid and galacturonic acid, together with galactose, minor amounts of arabinose, and relatively high proportions of rhamnose. The exudate from B. glaucescens is of particular interest in having high molecular weight, high intrinsic viscosity, and a high methoxyl content. The nitrogen content of all three gums is low, but amino acid analysis shows that proteinaceous components are involved, as in the gum exudates from other genera.     

Some structural features of a heteropolysaccharide from the leaves of the cactus Pereskia aculeata

A homogenous water-soluble mucilaginous heteropolysaccharide containing 3.5 % protein was isolated from the leaves of Pereskia aculeata. It contains arabinose, galactose, rhamnose and galacturonic acid in a molar ratio of 5.1:8.2:1.8:1.0 and, based on conventional polysaccharide analysis techniques, has a (1→4)-linked β-D-galactopyranosyl main chain partially substituted at O-3 by β-L-arabinopyranosyl units, which are, in turn, di-O-substituted at O-2 and O-4 by non-reducing end-groups of α-L-arabinofuranose. Also present are O-substituted units of galactopyranosyluronic acid, which are also present as non-reducing end-groups. They are then linked (1→2) to rhamnopyranosyl units. Aqueous solutions of the heteropolymer had a maximum viscosity at pH 4.5 and viscosity was reduced in the presence of salts over a wide range of pHs. The ¹³C NMR spectrum of the polysaccharide in DMSO indicated a great difference between the elevated segmental motion of the arabinosyl side chains and that of the core, since signals of the former were sharp and those of the latter extremely broad.     

Structural studies of an extracellular polysaccharide (S-198) elaborated by Alcaligenes ATCC 31853

The structure of an extracellular polysaccharide, S-198, elaborated by Alcaligenes ATCC 31853 has been investigated; methylation analysis, specific degradations, and ¹H-n.m.r. spectroscopy were the main methods used. It is suggested that the polysaccharide is composed of “repeating units” with the structure

A sugar residue in the chain may be either L-rhamnose or L-mannose and only ≈50% of the residues contain the branching α-L-rhamnopyranosyl group. The polysaccharide further contains O-acryl groups. It belongs to a group of polysaccharides, elaborated by Alcaligenes and Pseudomonas species, which all have the same linear backbone (except that some of them do not contain L-mannose) without branching or with branches that differ in their chemical structures and/or positions.     

Valorisation of chicken feathers for xanthan gum production using Xanthomonas campestris MO-03

Xanthan gum is an important commercial polysaccharide produced by Xanthomonas species. In this study, xanthan production was investigated using a local isolate of Xanthomonas campestris MO-03 in medium containing various concentrations of chicken feather peptone (CFP) as an enhancer substrate. CFP was produced with a chemical process and its chemical composition was determined. The addition of CFP (1–8?g/l) increased the conversion of sugar to xanthan gum in comparison with the control medium, which did not contain additional supplements. The highest xanthan production (24.45?g/l) was found at the 6?g/l CFP containing control medium in 54?h. This value was 1.73 fold higher than that of control medium (14.12?g/l). Moreover, addition of CFP improved the composition of xanthan gum; the pyruvate content of xanthan was 3.86% (w/w), higher than that of the control (2.2%, w/w). The xanthan gum yield was also influenced by the type of organic nitrogen sources. As a conclusion, CFP was found to be a suitable substrate for xanthan gum production.     

The gum exudates from Chloroxylon swietenia,Sclerocarya caffra,Azadirachta indica and Moringa oleifera

Analytical data are presented for the polysaccharide and proteinaceous components of the gum exudates from Chloroxylon swietenia and Sclerocarya caffra, and for the amino acid compositions of the exudates from Azadirachta indica (two specimens) and Moringa oleifera. The gums from C. swietenia and S. caffra contain 4-O-methylglucuronic acid, glucuronic acid, galactose and arabinose; rhamnose is absent. Amino acid analysis shows that proteinaceous material is present in the gums from C. swietenia, S. caffra and M. oleifera despite their low nitrogen content. Hydroxyproline accounts for 28 % of the amino acid content of S. caffra gum. In contrast, A. indica gum has a high nitrogen content but contains very little hydroxyproline.     

The structure of the neutral polysaccharide gum secreted by Rhizobium strain cb744

A previous investigation of the structure of the extracellular polysaccharide gum from the nitrogen-fixing Rhizobium strain cb744 (a member of the slow-growing Cowpea group) indicated that there were two β-(1→4)-linked d-glucopyranosyl residues for each α-(1→4)-linked d-mannopyranosyl residue, and that each mannose was substituted at O-6 by a β-d-galactopyranosyl residue having 71% of the galactose present as 4-O-methylgalactose. The present study shows that, although the gum appeared to have a simple tetrasaccharide repeating unit, it is composed of two closely associated components. One is a (1→4)-linked α-d-mannan substituted at each O-6 by a β-d-galactopyranosyl residue (71% 4-O-methylated). The second component is a (1→4)-linked β-d-glucan. The existence of the two polysaccharides was established by separation of the β-d-galactosidase-treated gum on a column of concanavalin A-Sepharose 4B. The d configurations were determined and the anomeric attribution of the linkages confirmed by the use of enzymes. The interaction between the two gum components is discussed.     

A Galacturonic Acid–Containing Xyloglucan Is Involved in Arabidopsis Root Hair Tip Growth

Root hairs provide a model system to study plant cell growth, yet little is known about the polysaccharide compositions of their walls or the role of these polysaccharides in wall expansion. We report that Arabidopsis thaliana root hair walls contain a previously unidentified xyloglucan that is composed of both neutral and galacturonic acid–containing subunits, the latter containing the β-d-galactosyluronic acid-(1→2)-α-d-xylosyl-(1→ and/or α-l-fucosyl-(1→2)-β-d-galactosyluronic acid-(1→2)-α-d-xylosyl-(1→) side chains. Arabidopsis mutants lacking root hairs have no acidic xyloglucan. A loss-of-function mutation in At1g63450, a root hair–specific gene encoding a family GT47 glycosyltransferase, results in the synthesis of xyloglucan that lacks galacturonic acid. The root hairs of this mutant are shorter than those of the wild type. This mutant phenotype and the absence of galacturonic acid in the root xyloglucan are complemented by At1g63450. The leaf and stem cell walls of wild-type Arabidopsis contain no acidic xyloglucan. However, overexpression of At1g63450 led to the synthesis of galacturonic acid–containing xyloglucan in these tissues. We propose that At1g63450 encodes XYLOGLUCAN-SPECIFIC GALACTURONOSYLTRANSFERASE1, which catalyzes the formation of the galactosyluronic acid-(1→2)-α-d-xylopyranosyl linkage and that the acidic xyloglucan is present only in root hair cell walls. The role of the acidic xyloglucan in root hair tip growth is discussed.     

On the Steric Configuration of the Urushi Polysaccharide

This paper presents the steric configuration of a polysaccharide obtained from the latex of the Japanese lacquer tree. Thus, the polysaccharide consisted of galactose and galacturonic acid, and the main chain of polysaccharide was proved to be linked with 1 → 3 linkage of galactose residue of 6-O-galacturonosyl galactose unit by the periodate oxidation method. The molecular weight was calculated to be 6 × 10⁴ by Archibald’s ultracentrifugal method. The configuration of the polysaccharide was discussed to be α helical structure of which one turn of the helices consists of 6 to 7 6-O-galacturonosyl galactose units and the diameter of the helix is 21 Å and one pitch is 9.5 Å on the basis of viscosity measurements, color reaction with iodine, crystallization with capronic acid and consideration of molecular models.     

The structure of Lannea humilis gum

Lannea humilis trees exude a water-soluble gum polysaccharide containing galactose (75%), arabinose (11%), rhamnose (2%), and uronic acids (12%). Three aldobiouronic acids are present (chromatographic analysis), namely 4-O-(α-D-galactopyranosyluronic acid)-D-galactose, 6-O-(β-D-glucopyranosyluronic acid)-D-galactose, and 6-O-(4-O-methyl-β-D-glucopyranosyluronic acid)-D-galactose. Linkage analysis of degraded gums A and B, obtained by controlled, acid hydrolysis, gave (chromatographic analysis) 3-O-β-L-arabinofuranosyl-L-arabinose, 3-O-β-L-arabinopyranosyl-L-arabinose, 3-O-α-D-galactopyranosyl-L-arabinose, 3-O-β-D-galactopyranosyl-D-galactose, and 6-O-β-D-galactopyranosyl-D-galactose. Degraded gums A and B were examined by methylation analysis, and the former was subjected to a Smith-degradation, giving degraded gum C, which was studied by linkage and methylation analysis. The O-methyl derivative of the whole gum was prepared (a) by the Haworth and Purdie procedures, and (b) by the sodium hydride-methyl iodide-methyl sulphoxide technique. Both products were examined, after methanolysis, by g.l.c.: 2,3,4-tri-O-methyl-L-rhamnose; 2,3,5- and 2,3,4-tri- and 2,5-di-O-methyl-L-arabinose; 2,3,4,6-tetra-, 2,3,6-, 2,4,6- and 2,3,4-tri-, 2,6- and 2,4-di-, and 2-O-methyl-D-galactose; 2,3,4-tri-O-methyl-D-glucuronic acid and 2,3,4-tri-O-methyl-D-galacturonic acid were identified. The whole gum was subjected to four successive Smith-degradations giving Polysaccharides I–IV, which were examined by linkage and methylation analysis. Polysaccharide IV is a branched galactan; the arabinose-containing sidechains in L. humilis gum therefore do not contain more than four residues, and only a few of that length occur. The evidence obtained indicates that the gum molecules are very highly branched. The galactan framework consists of short chains of β-(1→3)-linked D-galactose residues, branched and interspersed with β-(1→6)-linkages. To positions 3 and 6 of this framework are attached either single D-galactose end-groups or short side-chains of D-galactose or of L-arabinose residues, and three aldobiouronic acids. A possible structural fragment that shows these features is proposed.     

The composition and properties of the gum exudates from Terminalia sericea and T. Superba

The gum polysaccharides from Terminalia sericea and T. superba have been analysed. They have a complex sugar composition, containing galacturonic, glucuronic, and 4-O-methylglucuronic acids as well as galactose, arabinose, rhamnose, mannose and xylose. The exudates from T. sericea and T. superba are remarkably similar in composition, particularly with respect to their proportions of neutral sugars and total uronic acid content, although T. sericea gum contains considerably more 4-O-methylglucuronic acid than T. superba. Both gums are very viscous and dissolve readily to give solutions of good colour.!!     

Isolation of portulaca oleracea (regla) mucilage and identification of its structure

Portulaca oleracea leaves were found to contain 0.42% of a mucilage mixture. The mucilage was fractionated into an acidic and a neutral fraction. The acidic fraction consists of galacturonic acid residues joined by α-(1→4)-linkages; 60% of these residues are present as the calcium salt, and esterified galacturonic acid residues are absent. The neutral fraction is composed of 41% of arabinose and 43% of galactose residues, besides traces of rhamnose residues.     

Structure of the extracellular polysaccharide from xanthomonas campestris

Xanthan gum, the extracellular polysaccharide from Xanthomonas campestris, has been reinvestigated by methylation analysis, and by uronic acid degradation followed by oxidation and elimination of the oxidized residue. The polysaccharide is composed of pentasaccharide repeating-units with the following structure:

     

The preparation of a crystalline guanosine trialcohol and its sodium salt

A polysaccharide has been extracted from Cassia corymbosa seeds with cold, acidulated water, and purified to give a water-soluble product containing d-galactose and d-mannose in 4:7 molar ratio. Acid-catalyzed fragmentation, periodate oxidation, methylation, and enzymic hydrolysis showed that the seed gum has a branched structure consisting of a linear chain of β-d-(1→4)-linked mannopyranosyl units, some of which are substituted at O-6 by two α-d-(1→6) galactopyranosyl units mutually linked glycosidically. Methylation analysis of the galactomannan afforded 2,3,4-tri- and 2,3,4,6-tetra-O-methylgalactose, along with 2,3-di- and 2,3,6-tri-O-methylmannose, in the molar ratios of 2:2:2:5. Both the methylation and the periodate-oxidation studies showed ～36.4% of end groups. The significance of these results, together with the findings of partial hydrolysis with acid, are discussed, in relation to ascertaining the structure of the repeating unit of the polysaccharide.     

An anionic galactomannan polysaccharide gum from a newly-isolated lactose-utilizing bacterium. I. Strain description and gum characterization.

As part of an effort to obtain microorganisms able to produce polysaccharide gums from whey and whey permeate, soil samples from farm fields regularly treated with whey were screened for bacteria able to produce gums from lactose. The most promising organism isolated (ATCC 55046) is a facultative anaerobe, tentatively identified as a new Erwinia species on the basis of biochemical and morphological tests. The organism produces a polysaccharide gum from lactose and other sugars (herein named lactan gum) composed of mannose, galactose, and galacturonic acid with an approximate molar ratio of 5:3:2 and containing no organic acid modifying groups. The weight average molecular weight of the gum is approximately 7 x 10(6). Aqueous solutions of lactan gum exhibit shear-thinning and elastic flow behavior with an estimated power law model flow index of 0.26 at 1% (w/w) gum. The viscosity of aqueous 1% (w/w) lactan gum solutions is stable over a pH range of 2-11, being particularly stable in alkaline environments. Aqueous 1% (w/w) gum solutions at pH 5-11 show excellent thermostability, retaining at least 80% of the original viscosity after being heated to 121 degrees C for 15 min. These flow properties indicate potential industrial applications in food and nonfood products requiring a moderate degree of thickening, wet-end additives and coating agents for paper products, ceramics, detergents, and binders for building materials.     

The structure of lannea coromandelica gum

Lannea coromandelica trees exude a water-soluble gum polysaccharide containing galactose (70%), arabinose (11%), rhamnose (2%), and uronic acids (17%). Three aldobiouronic acids are present (chromatographic analysis), namely 4-O-(α-d-galactopyranosyluronic acid)-d-galactose, 6-O-(β-d-glucopyranosyluronic acid)-d-galactose, and 6-O-(4-O-methyl-d-glucopyranosyluronic acid)-d-galactose. Linkage analysis of degraded gum A, obtained by controlled, acid hydrolysis, gave (chromatographic analysis) 3-O-β-l-arabinofuranosyl-l-arabinose, 3-O-β-l-arabinopyranosyl-l-arabinose, 3-O-α-d-galactopyranosyl-l-arabinose, 3-O-β-d-galactopyranosyl-d-galactose, and 6-O-β-D-galactopyranosyl-d-galactose. Degraded gum A was examined by methylation analysis, and was subjected to a Smith-degradation, giving degraded gum B, which was studied by linkage and methylation analysis. The O-methyl derivative of the whole gum was prepared by the Haworth and Purdie procedures and examined, after methanolysis, by g.l.c.: 2,3,4-tri-O-methyl-l-rhamnose, 2,3,5- and 2,3,4-tri- and 2,5-di-O-methyl-l-arabinose; 2,3,4,6-tetra-, 2,3,6-, 2,4,6-, and 2,3,4-tri-, and 2,6- and 2,4-di-O-methyl-d-galactose; 2,3,4-tri-O-methyl-d-glucuronic acid and 2,3,4-tri-O-methyl-d-galacturonic acid were identified. The whole gum was subjected to three successive Smith-degradations, giving Polysaccharides I–III which were examined by linkage and methylation analysis. The structural evidence obtained indicates that the gum molecules are very highly branched, based on a galactan framework consisting of short chains of β-(1→3)-linked d-galactose residues, branched and interspersed with β-(1→6) linkages. To positions 3 and 6 of this framework are attached either single d-galactose end-groups or short side-chains of d-galactose or of l-arabinose residues, and three aldobiouronic acids. The structure therefore appears to be very similar to that established recently for Lannea humilis gum.