PubMed Health⌕ Search

Biomedical subjects

A Heyraud

Publications and source records attributed to A Heyraud.

30 records · Page 2Linked to original sources
PubMed1995

Galactomannans from Brazilian seeds: characterization of the oligosaccharides produced by mild acid hydrolysis.

Galactomannans with Man:Gal ratios ranging from 1.1:1 to 3:1, obtained from the seeds of Mimosa scabrella, Stryphnodendron barbatiman, Schizolobium parahybum and Schizolobium amazonicum, were submitted to mild acid hydrolysis. The products were fractionated by gel permeation chromatography on BioGel P2 yielding fractions with degrees of polymerization (DP) of 1 to 6. Those with DP 2 to 6 from each species were analysed by ion-exchange high-performance liquid chromatography and characterized by 13C- and 1H-nuclear magnetic resonance (NMR) spectroscopy. The distribution of the oligosaccharides of each degree of polymerization was very similar for the products from S. parahybum and S. amazonicum, indicating the same D-galactosyl distribution on the D-mannan backbone, in agreement with the 13C-NMR splitting in the C4 region of the D-mannosyl units in the original polymers. The hydrolytic conditions adopted allowed characterization of compounds that are not generally produced by enzymatic treatments. The results show that the structures of the oligosaccharides, even if there is a preferential hydrolysis of Gal-Man linkages, reflect the composition of the parent polymer.

Brazil↗
PubMed1995

Effects of salts on production and on O-acetylation of glucuronan excreted by the Rhizobium meliloti M5N1 CS strain.

Acetylation determined by 1H-nuclear magnetic resonance spectroscopy and production of the glucuronan excreted by the Rhizobium meliloti M5N1CS strain during cultivation in RCS medium with and without added magnesium salts have been studied. These salts induce an increase in the degree of substitution and the molar ratio of 2,3-di-O-acetyl residues. A decrease in production is observed after 75 h of fermentation as the magnesium salt concentration increases. The presence of manganese and sodium salts in the culture induces inhibition of exopolysaccharide (EPS) production. However, the structure of the EPS is similar to that of the EPS produced by standard fermentation, without modification in the degree of substitution.

Acetylation↗
PubMed1995

Cyclic (1-->2)-beta-D-glucans excreted by the glucuronan-producing strain Rhizobium meliloti M5N1CS (NCIMB 40472) and by the succinoglycan-producing strain Rhizobium meliloti M5N1.

During fermentation, the mutant strain Rhizobium meliloti M5N1CS, which induces nodule formation on alfalfa roots, produces a partially acetylated (1-->4)-beta-D-glucuronan. In addition to this exopolysaccharide of high molecular weight, the mutant strain produces oligoglucoronates and cyclic (1-->2)-beta-D-glucans with degrees of polymerization from 17 to 30. Under the conditions applied, magnesium has no effect on cyclic glucan production by the mutant strain, but the succinoglycan production by the wild-type strain Rhizobium meliloti M5N1 increases.

Acetylation↗
PubMed1994

Conformational study of digalacturonic acid and sodium digalacturonate in solution.

The solution conformation of digalacturonic acid and its sodium salt have been analyzed using nuclear magnetic resonance data and molecular mechanics calculations. The flexibility around the glycosidic linkage was characterized by calculation of the relaxed (phi, psi) potential surfaces for the isolated molecule, and also for dimethyl sulfoxide and aqueous solutions using the CHARMM and SOLVOL programs. The one-bond and three-bond proton-carbon couplings were measured and H-1'-H-4 distances were estimated from NOESY experiments. The calculated potential surfaces were used to determine theoretical ensemble averages of NMR data. The agreement between the experimental and theoretical data is very satisfactory. The calculations show a strong effect of solvent on the solution behavior of both compounds. The vacuum lowest energy conformer of digalacturonic acid is stabilized by solvation, while for sodium digalacturonate the solvent induces a conformational change. An extrapolation of the stable conformers to polysaccharide chains implies that poly(galacturonic acid) occurs in solution as a three-fold helix and sodium poly(galacturonate) as a two-fold helix.

Carbohydrate Conformation↗
PubMed1994

Stereochemical course of the hydrolysis reaction catalyzed by chitinases A1 and D from Bacillus circulans WL-12.

Chitinases A1 and D were purified from the periplasmic proteins produced by Escherichia coli HB101 harbouring recombinant plasmids carrying respectively the chiA and chiD genes of Bacillus circulans WL-12. HPLC analysis indicated that during the hydrolysis of chitotriose, both chitinases initially produce N-acetylglucosamine and only one anomer of chitobiose. 1H NMR spectroscopy of the hydrolysis of chitotetraitol showed that this anomer corresponds to beta-chitobiose, demonstrating that chitinases A1 and D act by a molecular mechanism that retains the anomeric configuration. This mechanism is similar to that of lysozymes although both chitinases belong to a family of proteins sharing no demonstrable amino acid sequence similarity with lysozymes.

Bacillus↗
PubMed1994

Physicochemical properties of extracellular (1-->4)-beta-D-glucuronan produced by the Rhizobium meliloti M5N1CS strain during fermentation: evidence of degradation by an exoenzyme activated by Mg2+.

The mutant Rhizobium meliloti M5N1CS (NCIMB 40472) produced a partially acetylated (1-->4)-beta-D-glucuronan during fermentation. The polysaccharide (EPS) extracted from broth during fermentation by microfiltration and ultrafiltration (using a 100 kDa cut-off membrane) was characterized by size exclusion chromatography. The weight-average molecular weight (Mw) of the EPS decreased from 7.5 x 10(5) to 5 x 10(5) between 27 and 75 h of fermentation. When MgSO4.7H2O (0.8 gl-1 per day) was present in the medium during the same period, the Mw of the EPS decreased to 1.5 x 10(5). Since EPS degradation was detected after microfiltration of the fermentation medium supplemented with magnesium, the Mw decrease of the EPS extracted during fermentation may be explained by enzymic degradation of the polymer activated by Mg2+ ions.

Bacterial Proteins↗
PubMed1993

Structural characterization and rheological properties of an extracellular glucuronan produced by a Rhizobium meliloti M5N1 mutant strain.

The mutant strain M5N1 C.S. (NCIMB 40472) of Rhizobium meliloti M5N1 is able to produce during fermentation a partially acetylated extracellular (1-->4)-beta-D-glucuronan. At low concentration (1 g.l-1), in the presence of monovalent cations, this new glucuronate behaves as a thickening agent, whereas at higher concentration a thermoreversible gel is obtained. With such divalent cations as Ca2+, a thermally stable gel can be formed.

Carbohydrate Sequence↗
PubMed1992

Stereochemistry of the hydrolysis reaction catalyzed by endoglucanase Z from Erwinia chrysanthemi.

Endoglucanase Z from the phytopathogenic bacterium Erwinia chrysanthemi (strain 3937) was purified by affinity chromatography on microcrystalline cellulose Avicel PH101. A kinetic characterization using p-nitrophenyl beta-D-cellobioside and p-nitrophenyl beta-D-lactosde as substrates was conducted: endoglucanase Z exhibited Km values of 3 mM and 7.5 mM and Vm values of 129 and 40 nmol.min-1.mg-1 towards p-nitrophenyl beta-D-cellobioside (kcat = 0.1 s-1) and p-nitrophenyl beta-D-lactoside (kcat = 0.03 s-1), respectively). The hydrolysis of cellotetraitol by endoglucanase Z was followed by HPLC and 1H NMR. Results show that cellobiitol and beta-cellobiose are initially formed, demonstrating that the enzyme is acting by a molecular mechanism retaining the anomeric configuration. This suggests the involvement of a glycosyl-enzyme intermediate.

Catalysis↗