Intra and inter generic homology in polysaccharide structure ofRhizobium andAlcaligenes

A study was conducted on the structure of extracellular, water-soluble polysaccharides from 5 different strains ofRhizobium viz. R. trifolii J60 andR. meliloti strains J7017, 202, 204 and 207. All these polysaccharides were found to contain glucose and galactose in the approximate molar ratio of 7:1. Methylation analysis revealed these polysaccharides to contain (1 → 3), (1 → 6), (1 → 4), (1 → 4, 1 → 6)-linked D-glucose residues, (1 → 3)-linked D-galactose and nonreducing terminal D-glucose attached to pyruvate. These polysaccharides were also found to be acylated by both acetyl and succinyl residue. This structure was found to be similar to that of succinoglycan, a succinic acid-containing water-soluble, extra-cellular polysaccharide elaborated byAlcaligenes faecalis var.myxogenes 10C3. This similarity in structure of polysaccharides from two different species ofRhizobium and also the polysaccharide produced byAlcaligenes has been discussed.     

Fragmentation analysis of extracellular acid polysaccharides from seven Rhizobium strains. Part I. D-glucuronic acid-containing oligosaccharides.

The extracellular, bacterial polysaccharides from seven Rhizobium strains have been submitted to partial hydrolysis with acid. Several neutral oligosaccharides, some containing pyruvic acid, were isolated together with D-glucuronic acid-containing oligosaccharides. The polysaccharide from Rh. meliloti did not contain glucuronic acid. For the other six strains, the following components were characterized: 4-O-(beta-D-glucopyranosyluronic acid)-D-glucuronic acid, 4-O-(beta-D-glucopyranosyluronic acid)-D-glucose, and O-(beta-D-glucopyranosyluronic acid)-(1leads to4)-O-(beta-D-glucopyranosyluronic acid)-(1leads to4)-D-glucose. These results indicate the presence of chains containing two beta-(1leads to4)-linked D-glucuronic acid residues, beta-linked to D-glucose at position 4.     

Rhizobium fredii and Rhizobium meliloti produce 3-deoxy-D-manno-2-octulosonic acid-containing polysaccharides that are structurally analogous to group II K antigens (capsular polysaccharides) found in Escherichia coli.

The polysaccharide components from cultured cells of Rhizobium fredii USDA205 and Rhizobium meliloti AK631 were extracted with hot phenol-water and separated by repetitive gel filtration chromatography. Polyacrylamide gel electrophoresis, nuclear magnetic resonance spectrometry, and gas chromatography analyses showed that both of these bacterial species produce unique polysaccharides that contain a high proportion of 3-deoxy-D-manno-2-octulosonic acid (Kdo). These polysaccharides, which constituted a major portion of the extracted carbohydrate, are not excreted into the growth media (i.e., they are not extracellular polysaccharides) and are structurally distinct from the lipopolysaccharides. The primary structure of the preponderant polysaccharide from R. fredii USDA205 was determined by high-performance anion-exchange liquid chromatography, nuclear magnetic resonance spectrometry, fast atom bombardment-mass spectrometry, and gas chromatography-mass spectrometry; it consists of repeating units of [-->3)-alpha-D-Galp-(1-->5)-beta-D-Kdop-(2-->]n. This molecule is structurally analogous to the constituents of one subgroup of K antigens (capsular polysaccharides) produced by Escherichia coli. Polysaccharides of this type have not previously been identified as components of rhizobial cells. The Kdo-containing polysaccharide from R. meliloti, which has not been completely characterized, appears to be structurally related to that of R. fredii.     

Mammalian-lung galactan

Exopolysaccharides of Agrobacterium tumefaciens and Rhizobium meliloti, containing d-glucose, d-galactose, pyruvic acid, and O-acetyl groups in the approximate proportions 6:1:1:1.5, were analysed by methylation. They were found to contain the following main structural units (all β-glycosidic): chain residues of (1→3)-linked d-glucose (24%), (1→3)-linked d-galactose (15%), (1→4)-linked d-glucose (20%), and (1→6)-linked d-glucose (18%); (1→4,1→6)-linked branching residues of d-glucose (12%), and terminal d-glucose residues substituted at positions 4 and 6 by pyruvate (11%). Uronic acid-containing exopolysaccharides of Rhizobium leguminosarum, R. phaseoli, and R. trifolii contained d-glucose, d-glucuronic acid, d-galactose, pyruvic acid, and O-acetyl groups in the approximate proportions 5:2:1:2:3. Methylation gave identical patterns of methylated sugar components, from which the following structural elements were deduced: chain residues of (1→3)-linked d-glucose substituted at positions 4 and 6 by pyruvate (13%), (1→4)-linked d-glucose (32%), and (1→4)-linked d-glucuronic acid (20%); (1→4,1→6)-linked branching residues of d-galactose and/or d-glucose (13%), and terminal d-glucose and/or d-galactose residues substituted at positions 4 and 6 by pyruvate (13%).     

Ultraviolet-irradiation induced and spontaneous mutation of Rhizobium trifolii 11B in relation to water-soluble and water-insoluble polysaccharide production ability

Rhizobium trifolii 11B was u.v. irradiated and nine u.v. mutants have been isolated. Among the mutants, only one, R. trifolii 21M11B, produced more (752 mg/100 ml) water-soluble polysaccharide than the parent (704 mg/100 ml). The composition of water-soluble polysaccharide from u.v. mutants differed from that of the parent, R. trifolii 11B, and none of its u.v. mutants produced water-insoluble polysaccharide as detected by the Aniline Blue method. Storage of u.v. mutants for 2 months at 5°C gave four spontaneous variants which acquired the ability to produce water-insoluble polysaccharide. The spontaneous mutants also retained their water-soluble polysaccharide producing ability. The water-soluble polysaccharide produced by these mutants was characterized as curdlan type. The chemistry of water-soluble and water-insoluble polysaccharides was also ascertained.     

Purification and chemical characterization of polysaccharides obtained from Lampteromyces japonicus by concanavalin A-sepharose affinity chromatography

Two classes of neutral polysaccharide which could not be separated from each other by conventional methods were isolated from the fungus, Lampteromyces japonicus, by affinity chromatography using concanavalin A-Sepharose. The polysaccharide retained on the concanavalin A-Sepharose column was eluted with 0.05 M methyl alpha-D-mannopyranoside and appeared to be alpha-mannan, while that which passed through the column was virtually all beta-glucan. Both polysaccharides were subjected to Smith-type degradation, methylation, acetolysis and glucosidase treatment. The results indicated that the alpha-mannan contained predominantly alpha-(1 leads to 2)-linked side chains branching from an alpha-(1 leads to 6)-linked backbone at the (1 leads to 2,6)-linked mannopyranosyl residues. Galactose was attached to approximately one-quarter of the non-reducing mannose terminals. The beta-glucan seemed to contain mainly (1 leads to 6)-linked side chains branching from a (1 leads to 3)-linked backbone at the (1 leads to 3,6)-linked glucopyranosyl residues.     

Extracellular polysaccharides of the genusRhizobium

This paper reports an investigation of the extracellular polysaccharides produced by 26 strains ofRhizobium andAgrobacterium. Strains ofRhizobium leguminosarum andR. phaseoli produced a water-soluble polysaccharide containing glucose, glucuronic acid and 4-0-methylglucuronic acid. These substances were also identified in the polysaccharide of a single strain fromLotus uliginosus. Glucose was the only detectable component in the polysaccharide produced by strains ofAgrobacterium radiobacter andA. tumefaciens. The polysaccharides obtained from slow-growing rhizobia were not freely water-soluble. Glucose, mannose, rhamnose, galactose and 4-0-methylglucuronic acid were identified as components of this extracellular material.These results are related to previous studies on rhizobial taxonomy and to the infection process in legumes.     

Acetylated methylmannose polysaccharide of Streptomyces.

A polysaccharide composed of 3-O-methyl-D-mannose and D-mannose in a molar ratio of approximately 10:1 and containing 3 to 4 esterified acetyl residues has been isolated from Streptomyces griseus. This acetylated methylmannose polysaccharide (AMMP) is similar to the methylmannose polysaccharide (MMP) of Mycobacterium smegmatis (Gray, G. R., and Ballou, C. E. (1971) J. Biol. Chem. 246, 6835-6842) in its size and composition, the absence of acidic or basic groups, and the lack of a reducing end. It is different, however, in its content of esterified acetyl residues, and it is slightly different in its structure and in its gel filtration properties. The structure of AMMP has been established by proton magnetic resonance spectroscopy, and by combinations of methylation analysis and Smith degradation utilizing non-radioactively labeled polysaccharide and [3H]methyl-labeled polysaccharide obtained from cells grown in the presence of L-[methyl-3H]methionine. It is concluded that AMMP is a linear, nonreducing, neutral polysaccharide composed of a terminal D-mannose residue linked alpha(1 leads to 4) to a chain of 10 consecutive alpha(1 leads to 4)-linked 3-O-methyl-D-mannose residues. The reducing terminal 3-O-methyl-D-mannose residue exists, at least in part, as its alpha-methyl glycoside. The positions of attachment of the ester residues have not been established.     

Structure of a highly pyruvylated galactan sulfate from the Pacific green alga Codium yezoense (Bryopsidales, Chlorophyta)

A polysaccharide fraction consisting of d-galactose, sulfate, and pyruvate in a molar proportion of 4:2:1 was isolated from the green seaweed Codium yezoense by water extraction followed by ion-exchange chromatography. To elucidate its structure, modified polysaccharides were prepared by desulfation, depyruvylation, and by total removal of non-carbohydrate substituents. Structures of the native polysaccharide and of the products of its chemical modifications were investigated by methylation analysis as well as by 1D and 2D (1)H and (13)C NMR spectroscopy. The polysaccharide devoid of sulfate and pyruvate was subjected to two subsequent Smith degradations to afford a rather low-molecular and essentially linear (1-->3)-beta-d-galactan. A highly ramified structure was suggested for the native polysaccharide, which contains linear backbone segments of 3-linked beta-d-galactopyranose residues connected by (1-->6) linkages, about 40% of 3-linked residues being additionally substituted at C-6, probably by short oligosaccharide residues also containing (1-->3) and (1-->6) linkages. Sulfate groups were found mainly at C-4 and in minor amounts at C-6. Pyruvate was found to form mainly five-membered cyclic ketals with O-3 and O-4 of the non-reducing terminal galactose residues. The minor part of pyruvate forms six-membered cyclic ketals with O-4 and O-6. The absolute configurations of ketals (R for six-membered ketals and S for five-membered ones) were established using NMR spectral data.     

Water-soluble polysaccharides from Ginkgo biloba leaves.

The water-soluble polysaccharides from dried Ginkgo biloba leaves were isolated after exhaustive extraction with organic solvents. The polysaccharide mixture could be separated into a neutral (GF1) and two acidic (GF2 and GF3) polysaccharide fractions by ion exchange chromatography. According to the Mr distribution GF1 and GF3 seemed to be homogenous, whereas GF2 could be further fractionated into two subfractions (GF2a and GF2b) by gel permeation chromatography. GF1 (Mr 23,000) showed the structural features of a branched arabinan. The main chain was composed of 1,5-linked arabinose residues and three in 12 arabinose molecules were branched via C-2 or C-3. GF2a (Mr 500,000) consisted mainly of 1,2,4-branched mannose (29%), 1,4-linked glucuronic (32%) and galacturonic (8%) acid as well as terminal rhamnose (25%). After removal of ca 70% of the terminal rhamnose the remaining polysaccharide showed a decrease in 1,2,4-branched mannose and an increase in 1,2-linked mannose indicating that at least half of the rhamnose residues were linked to mannose via C-4. GF3 (Mr 40,000) consisted of 1,4-linked galacturonic (30%) and glucuronic (16) acid, 1,3,6-branched galactose (15%), 1,2-linked (5%) and 1,2,4-branched (3.5%) rhamnose as well as 1,5-linked arabinose (11%). Rhamnose (5%) and arabinose (10%) were present as terminal groups. Mild acid hydrolysis selectively cleaved arabinose and the remaining polysaccharide showed an increased amount of 1,6-linked and terminal galactose and a decreased quantity of 1,3,6-branched galactose. These results indicated that the terminal as well as the 1,5-linked arabinose were mainly connected to galactose via C-3. The GF3 polysaccharide appeared to be a rhamnogalacturonan with arabinogalactan side chains.     

Construction of chimeric glucansucrases for analyzing substrate-binding regions that affect the structure of glucan products

A gene that encodes dextransucrase S (dsrS) from Leuconostoc mesenteroides NRRL B-512F encodes a glucansucrase dextransucrase S (DSRS) which mainly produces water-soluble glucan (dextran), while the dsrT5 gene derived from dsrT of the B-512F strain encodes an enzyme dextransucrase T5 (DSRT5), which mainly produces water-insoluble glucan. Tyr340-Asn510 of DSRS and Tyr307-Asn477 of DSRT5 (Site 1), Lys696-Gly768 of DSRS and Lys668-Gly740 of DSRT5 (Site 2), and Asn917-Lys1131 of DSRS and Asn904-Lys1118 of DSRT5 (Site 3) were exchanged and six different chimeric enzymes were constructed. Water-soluble glucan produced by recombinant DSRS was composed of 64% 6-linked glucopyranoside (Glcp), 9% 3,6-linked Glcp, and 13% 4-linked Glcp. Water-insoluble glucan produced by recombinant DSRT5 was composed of 47% 6-linked Glcp and 43% 3-linked Glcp. All of the chimeric enzymes produced glucans different from the ones produced by their parental enzymes. Some of the glucans produced by chimeric enzymes were extremely changed. The Site 1 chimeric enzyme of DSRS (STS1) produced water-soluble glucan composed mostly of 6-linked Glcp. That of DSRT5 (TST1) produced water-insoluble glucan composed mostly of 4-linked Glcp. The Site 3 chimeric enzyme of DSRS (STS3) produced mainly water-insoluble glucan, DSRT5 (TST3) produced mainly water-soluble glucans, and all of the glucan fractions consisted of 3-Glcp, 4-Glcp, and 6-Glcp. The amounts of the three linkages in the water-soluble glucan produced by TST3 were about 1:1:1. Site 1 was assumed to be important for making or avoiding making alpha-1,4 linkages, while Site 3 was assumed to be important for determining the kinds of glucosyl linkages made.     

Polysaccharide structure of tetrasporic red seaweed Tichocarpus crinitus

Sulfated polysaccharide isolated from tetrasporic plants of Tichocarpus crinitus was investigated. The polysaccharide was isolated by two methods: with water extraction at 80 °C (HT) and with a mild alkaline extraction (AE). The extracted polysaccharides were presented by non-gelling ones only, while galactose and 3,6-AG were the main monosaccharides, at the same time amount of 3,6-AG in AE polysaccharides was the similar to that of HT. According to methods of spectroscopy and mass spectrometry, the polysaccharide from tetrasporic T. crinitus contains main blocks of 1,3-linked β-d-galactopyranosyl-2,4-disulfates and 1,4-linked 3,6-anhydro-α-d-galactopyranosyl while 6-sulfated 4-linked galactopyranosyl resudies are randomly distributed along the polysaccharide chain. The alkaline treatment of HT polysaccharide results in obtaining polysaccharide with regular structure that composed of alternating 1,3-linked β-d-galactopyranosyl-2,4-disulfates and 1,4-linked 3,6-anhydro-α-d-galactopyranosyl residues. Native polysaccharide (HT) possessed both high anticoagulant and antiplatelet activity measured by fibrin clotting and platelet aggregation induced by collagen. This activity could be connected with peculiar chemical structure of HT polysaccharide which has high sulfation degree and contains also 3,6-anhydrogalactose in the polymer chain.     

Structure of the extracellular gelling polysaccharide produced by Enterobacter (NCIB 11870) species

The gelling polysaccharide produced by a species of Enterobacter (NCIB 11870) contains L-fucose, D-glucose, and D-glucuronic acid in the ratios 1:2:1. Analysis of the methylated and methylated, carboxyl-reduced polysaccharide revealed terminal non-reducing glucose, (1----3)-linked fucose, (1----3,1----4)-linked glucose, and (1----4)-linked glucuronic acid in the ratios 1:1:1.2:0.8. From the results of Smith degradation of the polysaccharide and spectroscopic studies of the acidic tetra- and octa-saccharides produced by bacteriophage-induced enzymic depolymerization of the polysaccharide, the following tetrasaccharide repeating-unit is proposed. (Formula: see text). This repeating-unit is identical to that of the capsular polysaccharide produced by Klebsiella aerogenes serotype K54 except for the absence of O-acetyl groups. The effects of the O-acetyl groups on the secondary structure and rheological properties of these polysaccharides are discussed.     

Use of fluorescence ratio imaging microscopy and flow cytometry for estimation of cell vitality for Bacillus licheniformis

The two main water-soluble extracellular polysaccharides produced by the basidiomycete fungus Pleurotus ostreatoroseus Sing were isolated and purified. They were characterized using 13C, 1H, and 1H, 13C HMQC NMR spectroscopy, methylation analysis, and Smith degradation. One was a mannan having a main chain of (1-->6)-linked alpha-D-mannopyranosyl residues, almost all of which were branched at O-2 with side chains of different lengths, containing 2-O- and 3-O-linked mannopyranosyl units. The other was a partially 3-O-methylated (1-->4)-linked alpha-D-galactopyranan, a structure that has not been previously described.     

Structural characterization of extracellular polysaccharides produced by the marine fungus Epicoccum nigrum JJY-40 and their antioxidant activities

Two extracellular polysaccharides, ENP1 and ENP2, were isolated from the fermentation liquid of the marine fungus Epicoccum nigrum JJY-40 by anion-exchange chromatography and gel-filtration chromatography, and their structures were investigated using chemical and spectroscopic methods including methylation analysis and NMR spectroscopy. The results demonstrated that ENP1 was composed of mannose, glucose, and galactose in the molar ratio of 5.0:2.1:1.0, and the main chain of the polysaccharide consisted of (1?→?2)-linked mannose, (1?→?3)-linked mannose, terminal mannose, (1?→?6)-linked glucose, (1?→?4)-linked glucose, and (1?→?4)-linked galactose. ENP2 was composed of mannose, galactose, glucose, and glucuronic acid in a molar ratio of 12.4:11.2:8.3:1.0, and its glycosidic linkage patterns included terminal mannose, (1?→?6)-linked glucose, (1?→?4)-linked galactose, and (1?→?3)-linked mannose. The two polysaccharides had a partially branched structure with branch point located at C-3 position of (1?→?6)-linked glucose residue. The molecular weights of ENP1 and ENP2 were 19.2 kDa and 32.7 kDa, respectively. Antioxidant properties of the two polysaccharides were evaluated with hydroxyl, superoxide, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities and lipid peroxidation inhibition in vitro, and results showed that ENP2 and ENP1 had good antioxidant activities, especially ENP2. ENP2 could be effective as a potential antioxidant.     

An extracellular polysaccharide produced by Zoogloea ramigera 115

A weakly acidic polysaccharide was purified from the extracellular zoogloeal matrix produced by Zoogloeal ramigera 115. The purified polysaccharide was homogeneous as judged by sedimentation analysis, and the average molecular weight was estimated to be about 10(5) by gel permeation chromatography of the fully methylated preparation. The polysaccharide was composed of D-glucose, D-galactose and pyruvic acid in an approximate molar ratio 11:3:1.5. On the basis of methylation, periodate oxidation, Smith degradation and partial hydrolysis, the following highly branched structure was deduced for the polysaccharide: a long chain mainly consisting of beta 1 leads to 4-linked glucose residues branching at the C-3 or C-6 position of galactose residues which are present in beta 1 leads to 4 or beta 1 leads to 3 linkages as the minor component of the long chain; pyruvic acid residues, the sole acidic component, are linked to the nonreducing end and/or 1,3-linked glucose residues through 4,6-ketal linkages. The purified polysaccharide was not readily soluble in water and had a high affinity for several metallic ions (e.g, 0.25 mumol Fe3+/mg, and 0.17 mumol Fe2+ mg). Upon addition of metallic ions (1 mM) to a gelatinous aqueous solution of the polysaccharide (K+ form, 0.125%), more than 80% of it immediately coprecipitated out with them.     

Structural elucidation of the predominant motifs of the major cell wall arabinogalactan antigens from the borderline species Tsukamurella paurometabolum and Mycobacterium fallax

Tsukamurella paurometabolum and Mycobacterium fallax are members of the suprageneric actinomycete group Corynebacterineae that possesses a cell wall skeleton composed of a peptidoglycan to which an arabinogalactan is covalently attached. This polysaccharide is further modified by esterification with C60-C80 mycolic acid residues in mycobacteria and T. paurometabolum. However, M. fallax and T. paurometabolum produce polyenoic (up to six double bonds) mycolic acids whereas the most common type of mycobacterial mycolates, called alpha-mycolates, are mono- and di-enoic or -cyclopropanated mycolic acids. To determine whether this difference also applied to the structures of cell wall arabinogalactans, competitive inhibition experiments using antibodies raised against the cell wall from Mycobacterium bovis and the arabinogalactans from T. paurometabolum and M. fallax were performed. They demonstrated the structural identity between the polysaccharide of M. fallax and those of mycobacteria and showed a strong similarity between the latter polysaccharides and that of T. paurometabolum. Structural analyses of the per-O-alkylated alditol fragments derived from the polysaccharides by gas chromatography-mass spectrometry (GC-MS) and 13C nuclear magnetic resonance (NMR) spectroscopy of the intact solubilized polysaccharides demonstrated that the polysaccharides from the two species analyzed contained all the major structural features previously characterized in mycobacterial arabinogalactans. These include (1) the homogalactan of alterning 5-linked galactofuranosyl (Galf) and 6-linked Galf residues, (2) a linear 5-linked arabino furanosyl (Araf), (3) a beta-Araf-(1-->2)-alpha-Araf disaccharide branched on both position 3 and position 5 of an alpha-Araf unit, and (4) a 5-linked-alpha-Araf unit branched on both position 3 and position 5 of an alpha-Araf residue. The polysaccharide from T. paurometabolum possesses additional structural domains composed of a terminal (t) Araf directly linked to either a 5-linked-alpha-Araf or to both position 3 and position 5 of a 3,5-linked alpha-Araf unit. Both the remarkable similarity of arabinogalactans from Corynebacterineae and their genus- and/or species-specificities are reflected in their 13C NMR spectra that may be used as a valuable help in the identification of members of the actinomycete group.     

Structural characterization and antioxidant activity of a polysaccharide from the fruiting bodies of cultured Cordyceps militaris

The water-soluble crude polysaccharides were obtained from the fruiting bodies of cultured Cordyceps militaris by hot water extraction followed by ethanol precipitation. The polysaccharides were successively purified by chromatography on DEAE–cellulose-52 and Sephacryl S-100 HR columns, giving main three polysaccharide fractions termed P50-1, P70-1, and P70-2. Structural features of P70-1 were investigated by a combination of chemical and instrumental analysis, such as partial acid hydrolysis, methylation analysis, periodate oxidation – Smith degradation, GC–MS, ¹³C NMR, HPAEC-PAD, and FT-IR. The results indicated that P70-1 has a backbone of (1 → 6)-linked β-d-mannopyranosyl residues, which occasionally branches at O-3. The branches were mainly composed of (1 → 4)-linked -d-glucopyranosyl and (1 → 6)-linked β-d-galactopyranosyl residues, and terminated with β-d-galactopyranosyl residues and -d-glucopyranosyl residues. In the in vitro antioxidant assay, P70-1 was found to possess hydroxyl radical-scavenging activity with an IC₅₀ value of 0.548 mg/ml.     

A sulfated galactan with antioxidant capacity from the green variant of tetrasporic Gigartina skottsbergii (Gigartinales, Rhodophyta)

The water soluble polysaccharide produced by the green variant of tetrasporic Gigartina skottsbergii was found to be composed of D-galactose and sulfate groups in a molar ratio of 1.0:0.65. (1)H and (13)C NMR spectroscopy studies of the desulfated polysaccharide showed a major backbone structure of alternating 3-linked β-D-galactopyranosyl and 4-linked α-D-galactopyranosyl units, and minor signals ascribed to 3-O-methyl-substitution on the latter unit. Ethylation analysis of the polysaccharide indicated that the sulfate groups are mainly located at position O-2 of 4-linked α-D-galactopyranosyl residue and partially located at positions O-6 of the same unit and at position O-2 of 3-linked β-D-galactopyranosyl residue, and confirmed the presence of 3-O-methyl-galactose in minor amounts (4.4%). The sulfated d-galactan presents a similar structure to λ carrageenan but with much lower sulfation at position O-6 of the α-residue and at position O-2 of β-residue. The antioxidant capacity of the sulfated d-galactan was evaluated by the peroxyl radicals (ORAC method), hydroxyl radicals, chelating activity, and ABTS(+) assays. Kinetic results obtained in these assays were compared with those obtained for the commercial λ carrageenan. The antioxidant activity toward peroxyl radicals was higher for commercial λ carrageenan, this agrees with its higher content of sulfate group. The kinetics of the reaction of both polysaccharides with hydroxyl and ABTS(+) radicals showed a complex mechanism, but the antioxidant activity was higher for the polysaccharide from the green variant of tetrasporic Gigartina skottsbergii.     

The molecular structures of a glucan and a galactan synthesised by Prototheca zopfii

When the unicellular organism Prototheca zopfii was grown on a malt-agar medium, a mixture of polysaccharides was synthesised which could be subsequently extracted from the dried cells with hot water and hot alkali. The major polysaccharide was a galactan which had a branched structure with main chains of (1→6)-linked D-galactopyranose residues, and ≈ 10% of side chains containing terminal D-galacto-furanose residues. A glycogen-type polysaccharide and a (1→4)-linked mannan were also produced.