D-glucose Residues Research Articles

Crystallinity and polysaccharide chains of β-glucan in white sorghum, SK 5912

The polysaccharide chains and the crystallinity of β-glucan in a white sorghum variety, SK 5912 were investigated using chemical and enzymic studies. Mild periodate oxidation and methylation, coupled to descending paper chromatography of products revealed the presence of unresolved non-carbohydrate moiety, 2, 4-and 2, 3-di- O-methyl d-glucose residues (molar ratio; 18:3) and 2, 4, 6-and 2, 3, 6-tri- O-methyl d-glucose residues (molar ratio; 1:14). Paper chromatography of the total acid hydrolysate also revealed a non-carbohydrate spot, identified as protein on the basis of positive Biuret and ninhydrin tests. The O-methyl d-glucose residues suggest two polysaccharide chains designated X and Y. Chain X is formed through linking of β- d-glucopyranosyl residues by (1→3) linkages with 85–86% (1→6) bonds at branch points and constitute about 6–7% of the β-glucan sample. Chain Y, which is 93–94% of the β-glucan polysaccharide chains, constitutes β- d-glucopyranosyl residues in (1→4) linkages and 4–5% (1→6) bonds at branch points. Of the 18 branch points on the X-chains in a given β-glucan sample, about 15 are the Y chains interlinked to the X-chains through their (Y-chains) reducing ends. Both acid and enzyme hydrolyses of the β-glucan suggest two structural organizations, a crystalline and less crystalline granules, based on two first order kinetics. This was correlated by the progress curves obtained during hydrolysis with two purified isoforms of β-glucanases from the sorghum malt. The short and highly branched polysaccharide chains, and longer but less branched polysaccharide chains found in this β-glucan are reminiscent of the structures of amylopectin and amylose, respectively. The K ms of 0.30–0.32 and 0.42–0.50 mg β-glucan/ml for the β-glucanase isoforms also lay credence to both the crystalline forms and the highly polymerised nature of the β-glucan in white sorghum.

Synthesis and Characterization of Well-Defined Chain-End- and In-Chain-Functionalized Polystyrenes with a Definite Number of d-Glucose and/or d-Galactose

The synthetic methodologies for various well-defined chain-end- and in-chain-functionalized polystyrenes with a definite number of d-glucose and/or d-galactose residues have been described. They are based on diverse modes of addition reactions of polystyryllithium with substituted 1,1-diphenylethylene derivatives with acetal-protected α-d-glucofuranose and α-d-galactopyranose residues, followed by deprotection. By employing these methodologies, chain-end-functionalized polystyrenes with 4, 6, and 8 d-glucose and/or d-galactose residues and in-chain-functionalized polystyrenes with 2, 4, 8, and 12 d-glucose residues were synthesized. These polymers all were precisely controlled with regard to molecular weight, molecular weight distribution, degree of functionalization, and functionalized position in a chain. Such functionalized polymers with monosaccharide residues aggregated possibly to form reversed micelles in cyclohexane at 39 °C. It was observed that the aggregation number increased as increasing with...

Gelation of periodate oxidised scleroglucan (scleraldehyde)

Polysaccharides such as scleroglucan and schizophyllan contain periodate-resistant β-1,3-linked d-glucan backbones with regularly distributed side chains consisting primarily of single β-1,6-linked d-glucose residues that are susceptible to periodate oxidation. Side chain oxidation results in the formation of dialdehyde groups and the production of formic acid. During the initial periodate oxidation an increase in the storage modulus ( G′) associated with the formation of gels, was observed when the reduced concentration, C p [ η] was above 3. These gels appeared to be physically stable, whereas aldehyde reduction (e.g. with NaBH 4) or oxidation to carboxyl (e.g. with NaClO 2 in acetic acid) dissolved the gels. The mechanism of cross-linking can be explained by the formation of intermolecular hemiacetal linkages. The gels were further characterised rheologically in terms of the initial increase in the storage modulus and the stability when stored in seawater at 55 and 90°C, respectively.

Stagonospora avenae secretes multiple enzymes that hydrolyze oat leaf saponins.

The phytopathogenic fungus Stagonospora avenae is able to infect oat leaves despite the presence of avenacoside saponins in the leaf tissue. In response to pathogen attack, avenacosides are converted into 26-desglucoavenacosides (26-DGAs), which possess antifungal activity. These molecules are comprised of a steroidal backbone linked to a branched sugar chain consisting of one alpha-L-rhamnose and two (avenacoside A) or three (avenacoside B) beta-D-glucose residues. Isolates of the fungus that are pathogenic to oats are capable of sequential hydrolysis of the sugar residues from the 26-DGAs. Degradation is initiated by removal of the L-rhamnose, which abolishes antifungal activity. The D-glucose residues are then hydrolyzed by beta-glucosidase activity. A comprehensive analysis of saponin-hydrolyzing activities was undertaken, and it was established that S. avenae isolate WAC1293 secretes three enzymes, one alpha-rhamnosidase and two beta-glucosidases, that carry out this hydrolysis. The major beta-glucosidase was purified and the gene encoding the enzyme cloned. The protein is similar to saponin-hydrolyzing enzymes produced by three other phytopathogenic fungi, Gaeumannomyces graminis, Septoria lycopersici, and Botrytis cinerea, and is a family 3 beta-glucosidase. The gene encoding the beta-glucosidase is expressed during infection of oat leaves but is not essential for pathogenicity.

Mechanism of the action of Leuconostoc mesenteroides B-512FMC dextransucrase: kinetics of the transfer of d-glucose to maltose and the effects of enzyme and substrate concentrations

The kinetics of the reaction of Leuconostoc mesenteroides B-512FMC dextransucrase with sucrose were studied. This enzyme catalyzes the synthesis of dextran from sucrose with a k cat of 641 s −1 and the transfer of d-glucose from sucrose to maltose with a k cat of 1070 s −1. The enzyme was also found to catalyze two new reactions in the absence of sucrose, using dextran as the substrate; d-glucose was transferred from the non-reducing ends of dextran chains to maltose with a relatively low k cat of 3.2 s −1; and d-glucose was hydrolyzed from the non-reducing ends of dextran chains with a very low k cat of 0.085 s −1. Ping-pong/bi-bi kinetics of these reactions are consistent with the formation of a glucosyl–enzyme covalent intermediate. It is shown that an increase in the concentrations of both maltose and sucrose in the d-glucose transfer reaction to maltose gives an exponential decrease in the amount of dextran and a concomitant increase in the amount of acceptor products. It is further shown that increasing the amount of dextransucrase gives a decrease in the amount of dextran and an increase in the amount of acceptor products, after the sucrose has been consumed. This anomaly occurs because the relatively high amounts of enzyme catalyze the transfer of d-glucose from the non-reducing ends of the dextran chains to maltose, giving a decrease in the amount of dextran and an increase in the amount of acceptor product. Further, the high amounts of enzyme catalyze the hydrolysis of the d-glucose residues from the ends of the dextran chains, giving a decrease in the amount of dextran. These reactions are not observed when lower amounts of enzyme are used, as the reactions are much slower than the synthesis of dextran and the usual acceptor transfer reactions of d-glucose from sucrose to acceptor.

Structural studies of resistant starch derived from processed (autoclaved) rice

Resistant starch (RS), isolated by hydrolysis with Termamyl, protease and amyloglucosidase, of five-cycle autoclaved rice was purified by size exclusion chromatography. Structural characterization by β-amylolysis, 13C NMR and methylation followed by GC-MS analysis revealed RS to be a linear (1→4)-α-d-glucan, originating probably from amylose. Its molecular weight was low, 1.20×106 Da, and amounted to 7400 d-glucose residues. X-ray diffraction measurements showed RS to have both B-type and V-type diffraction patterns. Differential scanning calorimetry data revealed the thermal stability characteristics of RS. The undigested material (equivalent to RS) recovered from the ileum of rat intestine exhibited an almost comparable GPC profile, molecular weight and λmax characteristics with those of in vitro isolated RS.

Isolation and chemical characterization of a capsular polysaccharide antigen shared by clinical isolates of Enterococcus faecalis and vancomycin-resistant Enterococcus faecium.

Enterococci are a common cause of serious infections, especially in newborns, severely immunocompromised patients, and patients requiring intensive care. To characterize enterococcal surface antigens that are targets of opsonic antibodies, rabbits were immunized with various gentamicin-killed Enterococcus faecalis strains, and immune sera were tested in an opsonophagocytic assay against a selection of clinical isolates. Serum raised against one strain killed the homologous strain (12030) at a dilution of 1:5,120 and mediated opsonic killing of 33% of all strains tested. In addition, this serum killed two (28%) of seven vancomycin-resistant Enterococcus faecium strains. Adsorption of sera with the homologous strain eliminated killing activity. The adsorbing antigens were resistant to treatment with proteinase K and to boiling for 1 h, but were susceptible to treatment with sodium periodate, indicating that the antigen inducing opsonic activity is a polysaccharide. Antibodies in immune rabbit sera reacted with a capsule-like structure visualized by electron microscopy both on the homologous E. faecalis strain and on a vancomycin-resistant E. faecium strain. The capsular polysaccharides from E. faecalis 12030 and E. faecium 838970 were purified, and chemical and structural analyses indicated they were identical glycerol teichoic acid-like molecules with a carbohydrate backbone structure of 6-alpha-D-glucose-1-2 glycerol-3-PO4 with substitution on carbon 2 of the glucose with an alpha-2-1-D-glucose residue. The purified antigen adsorbed opsonic killing activity from immune rabbit sera and elicited high titers of antibodies (when used to immunize rabbits) that both mediated opsonic killing of bacteria and bound to a capsule-like structure visualized by electron microscopy. These results indicate that approximately one-third of a sample of 15 E. faecalis strains and 7 vancomycin-resistant E. faecium strains possess shared capsular polysaccharides that are targets of opsonophagocytic antibodies and therefore are potential vaccine candidates.

A new bioactive steroidal saponin, furcreastatin, from the plant Furcraeafoetida

Microbial and plant secondary metabolites were screened for compounds that are selectively cytotoxic to mutant p53-expressing mouse fibroblasts. As a result, furcreastatin, a novel steroidal saponin, was isolated from an EtOH extract of the leaves of Furcraea foetida. Furcreastatin consisted of hecogenin as the aglycone and a hexasaccharide containing d-galactose, l-rhamnose and four d-glucose residues. The structure was determined to be (3β,5α,25 R)-3-hydroxyspirostan-12-one 3- O-[α- l-Rha p-(1→4)-β- d-Glc p-(1→3)-{β- d-Glc p-(1→3)-β- d-Glc p-(1→2)}-β- d-Glc p-(1→4)-β- d-Gal p] by extensive NMR spectroscopic studies. Furcreastatin decreased the viability of mutant p53-overexpressing cells with an ED 50 of 4.0 μg/mL, and decreased that of the parental cell-line with an ED 50 of 9.6 μg/mL.

Structural studies of the extracellular β- d-glucans from Phytophthora parasitica Dastur

Several extracellular glucans have been isolated from Phytophthora parasitica Dastur, a phytopathogenic fungus of the carnation. These polysaccharides consist of a mixture of (1→3)(1→6)-β- d-glucans whose molecular masses varied from 1×10 4 to 5×10 6 Da. All of these polysaccharides have a main chain of β-(1→3)-linked d-glucose residues substituted with mono-, di- and oligo-saccharidic chains attached through (1→6) linkages.

Preparation of spacer-containing di-, tri-, and tetrasaccharide fragments of the circulating anodic antigen of Schistosoma mansoni for diagnostic purposes

The chemical synthesis of β- d-Glc pA-(1⃗3)- β- d-Gal pNAc-(1⃗O)CH 2CH=CH 2, β- d-Gal pNAc-(1⃗6)-[ β- d-Glc pA-(1⃗3)]- β- d-Gal pNAc-(1⃗O)CH 2CH=CH 2, and β- d-Glc pA-(1⃗3)- β- d-Gal pNAc-(1⃗6)-[ β- d-Glc pA-(1⃗3)]- β- d-Gal pNAc-(1⃗O)CH 2CH=CH 2 is described. These oligosaccharides represent fragments of the circulating anodic antigen, secreted by the parasite Schistosoma mansoni in the circulatory system of the host. The applied synthesis strategy includes the preparation of a non-oxidised backbone oligosaccharide, with a levulinoyl group at O-6 of the β- d-glucose residue. After the selective removal of the levulinoyl group, the obtained hydroxyl functions were converted into carboxyl groups, using pyridinium dichromate and acetic anhydride in dichloromethane, to afford the desired glucuronic-acid-containing oligosaccharides. Subsequently, the allyl glycosides have been elongated with cysteamine to give the corresponding amine-spacer-containing oligosaccharides.

Measurement of interglycosidic 3JCH coupling constants of selectively 13C labeled oligosaccharides by 2D J-resolved 1H NMR spectroscopy

Tri-, tetra-, and penta-saccharide fragments of the O-specific polysaccharide of Shigella dysenteriae type 1 have been prepared in which a d-galactose residue of each oligosaccharide methyl glycoside derivative contains a 13C label at C-1. The interglycosidic coupling constants ( 3 J CH) of these 13C nuclei with the H-3 nuclei of the adjacent 2-acetamido-2-deoxy- d-glucose residues have been measured by two-dimensional, J-resolved 1H NMR spectroscopy. The magnitudes of these coupling constants indicate that the trisaccharide is conformationally different to the higher oligosaccharide homologs, in agreement with previous studies of 13C chemical shifts and 1 J CH values.

Chemoenzymatic synthesis of dendritic sialyl Lewis x

Traditional structure activity relationship studies (SAR) have led to the development of numerous sialyl Lewis x analogs in the search for potential antiinflammatory agents. However, these methods do not take into account cluster or multivalent effects. Reported herein is the chemoenzymatic synthesis of di-, tetra-, and octa-valent sLe x ligands scaffolded on dendrimers. Hypervalent l-lysine cores with covalently attached 2-acetamido-2-deoxy- d-glucose ( N-acetylglucosamine, GlcNAc) residues were chemically prepared and enzymatically transformed into sLe x-containing dendrimers so that multivalency, and its role in selectin-sLe x interactions may be evaluated. This work constitutes another successful enzymatic synthesis of sLe x and represents the first example of GlcNAc elongation on a synthetic dendrimer scaffold. These sLe x dendrimers are currently being investigated as selectin antagonists.

Proton NMR spectroscopy assignment of d-glucose residues in highly acetylated starch

1H NMR spectroscopy assignments have been obtained for starch acetates using COSY and HOHAHA experiments by comparison with the spectra of amylose triacetate and of peracetylated malto-oligosaccharides (maltotriose, maltotetraose, maltoheptaose). These assignments are valuable for the location and evaluation of the substitution pattern in modified starches. The bulk of the 1H NMR spectra of highly acetylated starch strongly resembles the spectrum of amylose triacetate in which all protons are identified and display distinct chemical shifts. The resolving power of the HOHAHA experiment allowed the distinction of minor spin systems. Beside these strong signals pertaining to an average 2,3,6-tri- O-acetyl- α-(1 → 4) linked d-glucopyranose unit in an infinite chain, the combination of COSY and HOHAHA experiments allowed the identification of these systems to the terminal, n-1, n-2, and to partially acetylated glucopyranosyl units. As an example, two different preparations of starch acetates with degrees of substitution 2.74 and 2.63 were examined. In one case, NMR demonstrates that the defects of acetylation are random on the polymeric chain (with corresponding signals for unacylated secondary hydroxyl positions at δ 3.61 and 3.40) while in another case, these signals are not detectable, probably due to the presence of clusters of non-acetylated residue forming solid-like zones.

Controlled synthesis of amphiphilic block copolymers with pendant glucose residues by living cationic polymerization

Amphiphilic block copolymers of vinyl ethers (VEs) of the type —[CH2CH(OCH2CH2OR)]m—[CH2CH(OiBu)]n—were synthesized by living cationic polymerization, where R is a D-glucose residue, and m and n are the degrees of polymerization (m = 20–50; n = 11–89). To obtain them, sequential living block copolymerization of isobutyl vinyl ether (IBVE) and the vinyl ether carrying 1,2:5,6-diisopropylidene-D-glucose residue was conducted by using the HCl adduct of IBVE, CH3CH(OiBu)Cl, as initiator in conjunction with zinc iodide. These precursor block copolymers had a narrow molecular weight distribution (M̄w/M̄n ∼ 1.1) and a controlled composition. Treatment of them with a trifluoroacetic acid/water mixture led to the target amphiphiles. The solubility of the amphiphilic block copolymers in various solvents depended strongly on composition or the m/n ratio. Their solvent-cast thin films were observed, under a transmission electron microscope, to exhibit various microphase-separated surface morphologies such as spheres, cylinders, and lamellae, depending on composition. © 1997 John Wiley & Sons, Inc.

Properties of auricularia auricula‐judae β‐D‐glucan in dilute solution

A water-soluble glucan A was isolated from the fruit body of Auricularia auricula-judae. It is composed of a backbone chain of beta-(1-->3)-linked D-glucose residues, two out of three glucose residues being substituted at C-6 positions with a single glucose unit. The weight average molecular weight Mw, number average molecular weight Mn, and intrinsic viscosity [eta] of the fractionated samples were studied at 25 degrees C in water and in dimethylsulfoxide (DMSO). The Mark-Houwink equation was established as [eta] = 6.10 x 10(-4) Mw1.14 for the glucan A having Mw ranging from 9 x 10(5) to 1.6 x 10(6) in water. The values of [eta] in water are far higher than those in DMSO, but the values of Mn measured in water are the same as those in DMSO. Analysis of Mw and [eta] in terms of the known theories for rods and wormlike chains yielded 1030 +/- 100 nm-1, 90 +/- 20 nm, 1.3 +/- 0.3 nm, and 0.26 +/- 0.03 nm for molar mass per unit contour length ML, persistence length q, diameter d, and contour length h per main-chain glucose residue, respectively. The present data suggest that glucan A dissolves in water as single-stranded helical chains and in DMSO as semiflexible chains.

Expression of Shigella dysenteriae serotype 1 O-antigenic polysaccharide by Shigella flexneri aroD vaccine candidates and different S. flexneri serotypes

The potential utility of Shigella flexneri aroD vaccine candidates for the development of bi- or multivalent vaccines has been explored by the introduction of the genetic determinants rfp and rfb for heterologous O antigen polysaccharide from Shigella dysenteriae serotype 1. The serotype Y vaccine strain SFL124 expressed the heterologous antigen qualitatively and quantitatively well, qualitatively in the sense of the O antigen polysaccharide being correctly linked to the S. flexneri lipopolysaccharide R3 core oligosaccharide and quantitatively in the sense that typical yields were obtained, with ratios of homologous to heterologous O antigen being 4:1 for one construct and 1:1 for another. Moreover, both polysaccharide chains were shown to be linked to position O-4 of the subterminal D-glucose residue of the R3 core. In contrast to the hybrid serotype Y SFL124 derivatives, analogous derivatives of serotype 2a vaccine strain SFL1070 did not elaborate a complete heterologous O antigen. Such derivatives, and analogous derivatives of rough, O antigen-negative mutants of SFL1070, formed instead a hybrid lipopolysaccharide molecule consisting of the S. flexneri lipid A R3 core with a single repeat unit of the S. dysenteriae type 1 O antigen. Introduction of the determinants for the S. dysenteriae type 1 O antigen into a second serotype 2a strain and into strains representing other serotypes of S. flexneri, revealed the following for the expression of the heterologous O antigen: serotypes 1a, 1b, 2a, and 5a did not produce the heterologous O antigen, whereas serotypes 2b, 3a, 3b, 4a, 4b, 5b, and X did.

A novel acidic glycogen extracted from the marine sponge Aplysina fulva (porifera-demospongiae)

Polysaccharides were extracted from the marine sponge Aplysina fulva by papain digestion and precipitation with cetylpyridinium chloride. Eluted from an anion-exchange column with a pH gradient, the sponge polysaccharides yielded two distinct fractions, denoted S1 and S2. The S1 fraction, which was eluted at low pH, constitutes about 0.2% of the sponge dry weight, migrates as a single band on agarose gel electrophoresis, and has a simpler chemical composition than the S2 fraction, which is eluted at more alkaline pH. The S1 fraction was further purified by ion-exchange and gel-permeation chromatography. Methylation, 1H and 13C NMR, amyloglucosidase digestion, specific optical rotation, infrared spectroscopy and the reaction with iodine established that the sponge glucan is a form of glycogen. However, the sponge polysaccharide, unlike oyster and rabbit liver glycogen, has an acidic property that causes it to bind to a DEAE-cellulose column at low ionic strength (pH 5.0). Chemical composition and infrared spectroscopy revealed considerable amounts of sulfate esters (≈ 0.05 moles/mole of glucose) in the sponge molecule. Comparative methylation analysis of the intact and desulfated S1 fraction suggests that about 50% of the non-reducing ends of the sponge polysaccharide are sulfated d-glucose residues, perhaps at position O-4.

Molecular and crystal structures of 2,3,4,6,1′,3′,4′,6′-octa- O-acetyl-β-sophorose, methyl 2,3,4,6,3′,4′,6′-hepta- O-acetyl-β-sophoroside, and methyl 2,3,4,6,3′,4′-hexa- O-acetyl-6′-deoxy-β-sophoroside

The molecular and crystal structures of 2,3,4,6,1′,3′,4′,6′-octa- O-acetyl-β-sophorose (β-sophorose octaacetate), methyl 2,3,4,6,3′,4′,6′-hepta- O-acetyl-β-sophoroside (methyl β-sophoroside heptaacetate), and methyl 2,3,4,6,3′,4′-hexa- O-acetyl-6′-deoxy-β-sophoroside (methyl 6′-deoxy-β-sophoroside heptaacetate) were determined by X-ray diffraction. All structures were obtained by the direct method and refined by the full-matrix least-squares procedure. The crystal data and final R values are as follows: (β-sophorose octaacetate, C 28O 19H 38, monoclinic, P2 1, a = 15.529(4), b = 10.958(2), c = 10.804(2) A ̊ , β = 107.73(3)°, D obsd = 1.285 g cm −3, D calcd = 1.288 g cm −3, Z = 2, R = 0.052, R W = 0.052 ; methyl β-sophoroside heptaacetate, C 27O 18H 38, orthorhombic, P2 12 12 1, a = 20.992(5), b = 27.642(7), c = 5.730(2) A ̊ , D obsd = 1.305 g cm −3, D calcd = 1.295 g cm −3, Z = 4, R = 0.064, R W = 0.066 ; methyl 6′-deoxy-β-sophoroside hexaacetate, C 25O 16H 36, hexagonal, P6 5, a = b = 15.136(2), c = 23.534(4) A ̊ , D calcd = 1.264 g cm −3, Z = 6, R = 0.079, R W = 0.064 . All the d-glucose residues have the 4 C 1 pyranose conformation. These three molecules interact with their surrounding molecules by van der Waals forces, only. Conformational angles of φ and ω at the β (1 → 2) glycosidic linkage of these compounds are similar to each other and close to the energetically minimum positions. All the primary acetate substituents at C-6 take a gauche-gauche conformation.

Synthesis of Sugar-Containing Macromonomers by Living Ring-Opening Polymerization

Abstract Well-defined α-styryl-type poly(2-methyl-2-oxazoline) and ω-acryl-type poly(2-phenyl-2-oxazoline) macromonomers having an N-acetylglucosamine (GlcNAc) or N-methyl GlcNAc residue at the other end were prepared by the cationic ring-opening polymerization of the corresponding 2-oxazolines. These macromonomers were radically copolymerized with styrene or acrylamide to yield the graft copolymers having the sugar moiety at the end of each branch. α-Styryl-type polyserine macromonomers with a D-glucose or GlcNAc residue in their repeating units were prepared by the anionic ring-opening polymerization of the respective sugar-substituted serine NCAs with p-vinylbenzyl amine and amine-terminated poly(2-methyl-2-oxazoline) macromonomers as initiators.

Structural features of fungal β- d-glucans for the efficient inhibition of the initiation of virus infection on Nicotiana tabacum

Glucans of fungal origin have been shown to inhibit the early stages of infection of Nicotiana by numerous viruses of different tzxonomic groups. Several glucans were isolated from the cell walls of Phytophthora parasitica, Phytophthora megasperma f. sp. glycinea ( Pmg) and Fusarium oxysporum, and their antiviral activity compared on tobacco leaves inoculated with tobacco mosaic virus. These polysaccharides consist of a mixture of (1 → 3)(1 → 6)-β- d-glucans with M r , varying from 1.1 × 10 3 to 2 × 10 6. Requirements for a prominent antiviral activity of the fungal polysaccharides are a β-(1 → 3)(1 → 6)- d-glucan structure with mono-, di-, tri- or tetra-glucosidic side branches attached to a linear main chain of β-(1 → 3)-linked- d-glucose residues. Very high activity is correlated with a high degree of branching at position 6 and with the size and glycosidic nature of the side chains. The molecular masses and the organized structure of fungal β- d-glucans are not essential for their antiviral activity. The structural motif for antiviral activity in Nicotiana is distinct from that required for elicitation of phytoalexins in soybean cotyledons.