Utilization of degraded peach gum polysaccharide by Aspergillus flavus

d-Galactose, d-mannose, d-xylose, l-arabinose, and d-glucuronic acid and its γ-lactone were examined as carbon sources for the culture of Aspergillus flavus. d-Mannose was taken up the most rapidly and d-glucuronic acid and its γ-lactone the least rapidly. A partially degraded polysaccharide from peach tree gum (Prunus persica [L.] Batsch containing the above sugars together with d-glucuronic acid and its 4-O-methyl ether was used as substrate for another A. flavus culture. It was found that d-galactose was the major sugar passing into the culture medium with lower proportions of d-xylose, l-arabinose, 2-O-β-d-glucopyranuronosyl-d-mannose, and 6-O-β-d-glucopyranuronosyl-d-galactose. This indicates that the fungus produces extracellular exo- and endo-glycanohydrolases which may be useful in structural studies on polysaccharides.     

Isolation and chemical characterization of compounds isolated fromAspergillus flavus conidia

Three types of heterogenous preparations and four types of preparations of polysaccharide nature were obtained in studies aimed at the isolation of active compounds fromAspergillus flavus conidia bearing their biological stimulatory activity. Extraction with trichloroacetic acid at 0 °C yielded a preparation in which the protein component predominated over the polysaccharide moiety at a ratio of 3: 1. In the preparation isolated from the phenolic phase of the phenol—water mixture at 68 °C the protein polysaccharide ratio was 1 : 1. In the material extracted in the aquoues phase and in that obtained by extraction with acetic acid at 100 °C the polysaccharide portion highly predominated (8 : 1 and 7 : 1 respectively).     

New structural features of the polysaccharide from gum ghatti (Anogeissus latifola)

Methylation and 13C NMR analyses were carried out on the high-arabinose, acidic heteropolysaccharide of gum ghatti and the products obtained on three successive, controlled Smith degradations. The side chains contained mainly 2-O- and 3-O-substituted Araf units. Of these the second degradation eliminated remaining alpha-Araf units, and their beta anomers became evident. The proportion of Galp units gradually increased in the form of nonreducing end- and Galp units, although 3,6-di-O- and 3,4,6-tri-O-substituted Galp units diminished. After three degradations groups with consecutive 3-O-substituted beta-Galp units were formed. The proportion of periodate-resistant 3-O- and 2,3-di-O-substituted Manp units was maintained. As a guide to side-chain structures in the polysaccharide, seven of the 10 free reducing oligosaccharide fractions (PC) present in the gum were isolated and examined (NMR, ESIMS, and sometimes methylation analysis). Characterized are alpha-Araf-(1 --> 2)-Ara and three Ara-containing oligosaccharide fractions containing 2-O- and 3-O-substituted units. These gave respectively, ESIMS molecular ions arising from Ara(2), beta-Araf oligosaccharides with four units, beta-Araf oligosaccharides with seven units, and Hex(2)-Ara(4). Alpha-Rhap-(1 --> 4)-GlcA, alpha-Rhap-(1 --> 4)-beta-GlcpA-(1 --> 6)-Gal, and alpha-Rhap-(1 --> 4)-beta-GlcpA-(1 --> 6)-beta-Galp-(1 --> 6)-Gal represented other side chains.     

Structural studies of gum arabic, the exudate polysaccharide from Acacia senegal

A 25.182-MHz ¹³C-n.m.r. spectrum of gum arabic allows unambiguous characterisation of all the C-1 resonances. These assignments have been confirmed by correlation of the modification of the intensities of these signals after controlled acid hydrolysis and characterisation of the released fragments. The resonances of the other carbons have been assigned through partial relaxed T₁ spectra of the polysaccharides obtained by graded degradation of the gum. These results indicate gum arabic to consist mainly of a (1→3)-β- -galactan core with (1→6)-β- -galacto-pyranosyl branches and with - -arabinofuranosyl-(1→3)-- -arabinofuranosyl and - -rhamnopyranosyl-(1→4)-β- -glucopyranosyluronic acid groups attached to positions 3 and 6, respectively, of the branch units.     

Partial structural studies of four Acacia gum exudates of the series phyllodineae

Methylation and hydrolysis studies have shown that gum specimens from Acacia difformis, A. mabellae, A. retinodes and A. rubida, which belong to Bentham's Series I (Phyllodineae), subseries 6F (Uninerves Racemosae), are similar structurally to those from A. podalyriifolia and A. pycnantha. This is further evidence that A. cyanophylla, which was placed next to A. pycnantha by Bentham, is atypical of the Series I Acacias.     

Polysaccharide of nectarine gum exudate: Comparison with that of peach gum

The gum exudate polysaccharide from the trunk of nectarine (PPNEC) was compared with that of peach, being composed of Ara, Xyl, Man, Gal, and uronic acids in 37:13:2:42:6 molar ratio and had M_w 3.93 × 10⁶ g mol^?1, compared with 5.61 × 10⁶ g mol^?1 for peach gum polysaccharide. Methylation analysis of PPNEC indicated a highly branched structure with relatively high amounts of di- (16%) and tri-O-substituted (9%) Galp units and nonreducing end-units of Araf (26%) and Xylp (17%). Combination with ¹³C NMR data, showed the presence of α-l-Araf (nonreducing end, 3-O-, 5-O-, and 2,5-di-O-subst.), β-l-Arap (4-O- and 2,4-di-O-subst.), β-d-Galp (3-O-, 2,3-di-O-, 3,6-di-O-, and 3,4,6-tri-O-subst.), and α- and/or β-d-Xylp nonreducing end-units. A signal appeared from 4-O-Me-α-d-GlcpA units. PPNEC had structures similar to those of polysaccharide from peach tree gum, although in different proportions and with a lower M_w.     

DNA restriction enzyme fragment polymorphism as a tool for rapid differentiation ofAspergillus flavus fromAspergillus oryzae

Aspergillus flavus andAspergillus oryzae are difficult to differentiate using standard morphologically based characteristics. This survey, using several restriction enzymes, showed thatSmaI digestions of total DNA could be used to differentiate these two closely related species ofAspergillus. A different electrophoretic pattern was associated with each of the two species, while within a species the pattern remained constant. CsCl banding of DNA from one isolate of each species indicated the DNA that produced the species-specific pattern was associated with the nuclear DNA fraction.     

Structural studies of gellan gum,an extracellular polysaccharide elaborated by Pseudomonas elodea

The structure of gellan gum, a polysaccharide of potential commercial usefulness elaborated by Pseudomonas elodea, has been investigated. It is concluded that the polysaccharide is composed of tetrasaccharide repeating-units having the following structure.

Of the repeating units, ～25% contain an O-acetyl group linked to C-6 of one of the β-d-glucopyranosyl residues.     

Evidence for microbial polysaccharide preparations containing polyester substituents

CPMAS 13C-n.m.r. spectroscopy was employed to characterize the composition and solid phase morphology of gellan, welan, rhamsan and NW11. Spectra indicated that commercial preparations of these polysaccharides, which share a similar molecular backbone, contain a non-carbohydrate component exhibiting four inequivalent carbon atoms. Isolation of this component, followed by 13C-n.m.r. in CHCl3 and MS analysis, revealed its structure to be poly(beta-hydroxybutyrate). Evidence is presented which suggests that this polyester may be a covalent adduct to the above polysaccharides, although this cannot be unambiguously determined at this time. Further experimentation is in progress.     

Synthesis of chitin by particulate preparations from Aspergillus flavus

Cell-free extracts from Aspergillus flavus catalyzed the synthesis of chitin from UDP-GlcNAc. Most of the activity was associated with membrane-rich fractions whereas no activity was detected in the cell walls. Chitin synthetase was activated by fungal acid proteases; animal and plant proteases destroyed it. Upon incubation at 0 C and 28 C chitin synthetase was inactivated, probably by the action of proteases present in the particulate preparations. Maximal activity was obtained at pH 6.6–7.1 and 15 C. Arrhenius plot showed a biphasic curve with the transition at 7 C. E values were 3300 Kcal/mole above this temperature and 15500 Kcal/mole below it. The enzyme was activated by GlcNAc and required a divalent metal, the most active being Mg⁺⁺. By plotting v vs UDP-GlcNAc concentration a sigmoidal curve was obtained. Km calculated at high substrate concentrations was 20mm. Chitin synthetase was competitively inhibited by polyoxin D (Ki 6.5 m) and UDP (Ki 1.35mm), the latter giving complex kinetics.This work was supported by grants No. 020 and 847 of the Consejo Nacional de Ciencia y Tecnología, México.Part of this work was carried out while the authors were research visitors at the Department of Plant Pathology, University of California, Riverside.     

Smith degradation of the O-antigenic polysaccharide of Salmonella Dakar: structural studies of the products

Two different oligosaccharides were obtained from the Smith degradation of the O-polysaccharide isolated from the lipopolysaccharide of Salmonella Dakar. The structures of these oligosaccharides were investigated by chemical analysis, NMR spectroscopy and MALDI-TOF mass spectrometry. The following structures of these products were determined: alpha-D-GalpNAc-(1-->4)-alpha-D-Quip3NAc-(1-->3)-alpha-L-Rhap-(1-->2)-threitol and [FORMULA: SEE TEXT] where Quip3NAc is 3-acetamido-3,6-dideoxyglucose. The reaction products confirmed the structure of the repeating unit of the Salmonella Dakar O-polysaccharide reported previously [Kumirska, J.; Szafranek, J.; Czerwicka, M.; Paszkiewicz, M.; Dziadziuszko, H.; Kunikowska, D.; Stepnowski, P. Carbohydr. Res. 2007,342, 2138-2143].     

槐豆胶与黄原胶的协效性研究

对槐豆胶与黄原胶的协效性进行了研究,结果表明,槐豆胶和黄原胶有较高的协效性,其最佳配比（重量比）为2：8;当混合液浓度达到0.5%-0.6%时形成凝胶,因此槐豆胶可作为黄原胶的增稠剂和凝胶剂。     

The molecular characterization of the polysaccharide gum from Laguncularia racemosa

A polysaccharide isolated from the exudate of Laguncularia racemosa, (Combreta-ceae) has been investigated using Smith-degradation, methylation analysis, hydrolysis, and ¹³C-NMR spectroscopy. The backbone of the structure is constituted of uronic acids, galactose and rhamnose. A complex pentasaccharide, constituted of these sugars, was isolated from the original gum and degradation products. This oligosaccharide is, probably, the main structural feature of the investigated polysaccharide. On the other hand, according to chemical and spectral evidence rhamnose is present, predominantly as internal residues. Arabinosyl (pyranosyl and furanosyl) residues and some galactosyl, glucuronic acid and 4-0-methyl--D-glucuronic acid residues are located in branches.     

Enzyme processivity changes with the extent of recalcitrant polysaccharide degradation

Glycoside hydrolases depolymerize polysaccharides. They can subtract single carbohydrate chains from polymer crystals and cleave glycosidic bonds without dissociating from the substrate after each catalytic event. This processivity is thought to conserve energy during polysaccharide degradation. Herein, we compare the processivity of components of the chitinolytic machinery of Serratia marcescens. The two processive chitinases ChiA and ChiB, the ChiB-W97A mutant, and the endochitinase ChiC were analyzed for the extent of degradation of three different chitin substrates. Moreover, enzyme processivity was assessed on the basis of the [(GlcNAc)2]/[GlcNAc] product ratio. The results show that the apparent processivity (Papp) greatly diminishes with the extent of degradation and confirm the hypothesis that Papp is limited by the length of obstacle free path on the substrate.     

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.     

Structural features of a water soluble gum polysaccharide from Murraya paniculata fruits

A water soluble gum polysaccharide was isolated from Murraya paniculata fruits. Hydrolytic experiments, methylation analysis, periodate oxidation studies and NMR data revealed that the polysaccharide was extensively branched and it consisted of 1,3-, and 1,3,6-linked beta-D-galactopyranosyl units, terminal beta-D-galactopyranosyl units and terminal alpha-D-glucopyranosyl 1,4-beta-D-galactopyranosyl units. Small amounts of 4-O-methylglucuronic acid residues were also present.