Phenolic components of the primary cell wall. Feruloylated disaccharides of D-galactose and L-arabinose from spinach polysaccharide

Food-derived carbohydrates--structural complexity and functional diversity

Carbohydrates are biomolecules abundantly available in nature. They are found in bewildering types ranging from simple sugars through oligo- and polysaccharides to glycoconjugates and saccharide complexes, each exhibiting characteristic bio-physiological and/or nutritional functions both in in vivo and in vitro systems. For example, their presence or inclusion in food dictates the texture (body) and gives desirable customer appeal (satisfaction), or their inclusion in the diet offers beneficial effects of great therapeutic value. Thus, carbohydrates are integrally involved in a multitude of biological functions such as regulation of the immune system, cellular signaling (communication), cell malignancy, antiinfection responses, host-pathogen interactions, etc. If starch is considered the major energy storage carbohydrate, the gums/mucilages and other non-starch carbohydrates are of structural significance. The most investigated properties of starch are its gelatinization and melting behavior, especially during food processing. This has led to the development of the food polymer science approach, which has enabled a new interpretive and experimental frame work for the study of the plasticizing influence of simple molecules such as water, sugars, etc. on food systems that are kinetically constrained. Starch, although considered fully digestible, has been challenged, and starch is found to be partly indigestible in the GI tract of humans. This fraction of starch-resisting digestion in vivo is known as resistant starch (RS). The latter, due to its excellent fermentative capacity in the gut, especially yielding butyric acid is considered a new tool for the creation of fiber-rich foods, which are of nutraceutical importance. By a careful control of the processing conditions the content of RS, a man-made fiber, can be increased to as high as 30%. Arabinoxylans are the major endospermic cell wall polysaccharides of cereals. In wheat they are found complexed with ferulic acid esters, which after oxidative coupling in vivo mediated by H2O2 and peroxidases or even by photochemical means give cross linked diferuloyl derivatives. The latter confer strength and extensibility to the cell wall and offer resistance for digestibility by ruminants. They also help blocking of the ingress of pathogens. The ester bound ferulic acid after oxidation in vivo generates reactive oxygen species that contribute to the fragmentation of non-starch polysaccharides (hemicelluloses), and thereby reduces the product viscosity, a property seen during long-term storage of rice. In plant tissues, the arabinogalactans are implicated in such diverse functions as cell-cell adhesion, nutrition of growing pollen tubes, response to microbial infections, and also as markers of identity expressed in the terminal sequences of saccharide chains.

Patterns of methyl and O-acetyl esterification in spinach pectins: new complexity

Driselase-digestion of cell walls from suspension-cultures of spinach (Spinacia oleracea L.), followed by anion-exchange chromatography, gel-permeation chromatography, preparative paper chromatography and preparative paper electrophoresis, yielded ten uronic acid-containing products in addition to free galacturonic acid (GalA). These included 4-O-methylglucuronic acid, alpha-L-rhamnopyranosyl-(1-->4)-D-glucuronic acid and several oligosaccharides containing GalA residues. The structures were unambiguously determined by a combination of 1- and 2-dimensional NMR spectroscopic techniques. Five of the six homogalacturonan-derived oligosaccharides purified contained 3-O-acetyl-GalA residues; however, methyl-esterified GalA residues occurred adjacent to both 2-O-acetyl-GalA and 3-O-acetyl-GalA residues. An acetylated, rhamnogalacturonan-I-derived oligosaccharide that was purified also contained 3-O-acetyl-GalA residues. Taken together with published data, our findings indicate considerable diversity in the patterns of pectin esterification. The implications for the action of pectin esterases are discussed.

Synthesis and characterization of N-coumaroyltyramine as a potent phytochemical which arrests human transformed cells via inhibiting protein tyrosine kinases

Numerous phytochemicals are believed to have beneficial effects on human health. N-Coumaroyltyramine accumulates in plants in response to wounding and pathogen attack. Due to the scarcity of N-coumaroyltyramine, its biological activities have not been studied in human cells. In this study, N-coumaroyltyramine was chemically synthesized and then purified by an HPLC with a UV-visible absorbance detector. Retention times of major peaks were 14.3 and 20.7 min, and the peak at 20.7 min was confirmed by LC-MS as N-coumaroyltyramine with a mass/charge (m/z) unit of 284.1. The synthesis procedure was relatively easy and had an acceptable yield (approximately 55%). The compound exhibited a new activity, suppression of growth of human tumor cells such as U937 and Jurkat cells. In addition, the suppressed growth of the cells was strongly associated with an increased percentage of cells in the S phase of the cell cycle progression. Furthermore, N-coumaroyltyramine was able to inhibit the protein tyrosine kinases including epidermal growth factor receptor (EGFR). This is the first report of the growth suppressing activity of N-coumaroyltyramine and its arrest of cells at the S phase of the cell cycle, possibly by inhibition of protein tyrosine kinases.

Fingerprinting of polysaccharides attacked by hydroxyl radicals in vitro and in the cell walls of ripening pear fruit

Hydroxyl radicals (*OH) may cause non-enzymic scission of polysaccharides in vivo, e.g. in plant cell walls and mammalian connective tissues. To provide a method for detecting the action of endogenous *OH in vivo, we investigated the products formed when polysaccharides were treated with *OH (generated in situ by ascorbate-H(2)O(2)-Cu(2+) mixtures) followed by NaB(3)H(4). Treatment with *OH increased the number of NaB(3)H(4)-reacting groups present in citrus pectin, homogalacturonan and tamarind xyloglucan. This increase is attributed partly to the formation of glycosulose and glycosulosuronic acid residues, which are then reduced back to the original (but radioactive) sugar residues and their epimers by NaB(3)H(4). The glycosulose and glycosulosuronic acid residues were stable for >16 h at 20 degrees C in ethanol or buffer (pH 4.7), but were destroyed in alkali. Driselase-digestion of the radiolabelled polysaccharides yielded characteristic patterns of (3)H-products, which included galactose and galacturonate from pectin, and isoprimeverose, galactose, glucose and arabinose from xyloglucan. Pectin yielded at least eight (3)H-labelled anionic products, separable by electrophoresis at pH 3.5. The patterns of radioactive products form useful 'fingerprints' by which *OH-attacked polysaccharides may be recognized. Applied to the cell walls of ripening pear (Pyrus communis) fruit, the method gave evidence for progressive *OH radical attack on polysaccharides during the softening process.

Isolation and characterization of human colonic bacteria able to hydrolyse chlorogenic acid

AIMS

Conjugated hydroxycinnamates, such as chlorogenic acid (caffeoyl-quinic acid), are widely consumed in a Western diet, coffee being one of the richest sources. Ingested hydroxycinnamate esters can reach the large intestine essentially unaltered, and may then be hydrolysed by esterases produced by the indigenous microflora. This study is aimed at identifying bacterial species responsible for the release of natural antioxidants, such as hydroxycinnamic acids, in the human large intestine.

METHODS AND RESULTS

Thirty-five isolates recovered after anaerobic batch culture incubation of human faecal bacteria in a chlorogenic acid-based medium were screened for cinnamoyl esterase activity. Six isolates released the hydroxycinnamate, ferulic acid, from its ethyl ester in a plate-screening assay, and these were identified through genotypic characterization (16S rRNA sequencing) as Escherichia coli (three isolates), Bifidobacterium lactis and Lactobacillus gasseri (two strains). Chlorogenic acid hydrolysing activities were essentially intracellular. These cinnamoyl esterase-producing organisms were devoid of other phenolic-degrading activities.

CONCLUSION

The results show that certain gut bacteria, including some already recognized as potentially health-promoting (i.e. species belonging to the genera Bifidobacterium and Lactobacillus), are involved in the release of bioactive hydroxycinnamic acids in the human colon.

SIGNIFICANCE AND IMPACT OF THE STUDY

Free hydroxycinnamates, including caffeic, ferulic and p-coumaric acids, exhibit antioxidant and anticarcinogenic properties both in vitro and in animal models. Given that the gut flora has a major role in human nutrition and health, some of the beneficial effects of phenolic acids may be ascribed to the microflora involved in metabolism.

Ferulic acid is esterified to glucuronoarabinoxylans in pineapple cell walls

The ester-linkage of ferulic acid (mainly E) to polysaccharides in primary cell walls of pineapple fruit (Ananas comosus) (Bromeliaceae) was investigated by treating a cell-wall preparation with 'Driselase' which contains a mixture of endo- and exo-glycanases, but no hydroxycinnamoyl esterase activity. The most abundant feruloyl oligosaccharide released was O-[5-O-(E-feruloyl)-alpha-L-arabinofuranosyl](1-->3)-O-beta-D-xylopyranosyl-(1-->4)-D-xylopyranose (FAXX). This indicated that the ferulic acid is ester-linked to glucuronoarabinoxylans in the same way as in the primary walls of grasses and cereals (Poaceae). Glucuronoarabinoxylans are the major non-cellulosic polysaccharides in the pineapple cell walls.

A modular cinnamoyl ester hydrolase from the anaerobic fungus Piromyces equi acts synergistically with xylanase and is part of a multiprotein cellulose-binding cellulase-hemicellulase complex

A collection of clones, isolated from a Piromyces equi cDNA expression library by immunoscreening with antibodies raised against affinity purified multienzyme fungal cellulase-hemicellulase complex, included one which expressed cinnamoyl ester hydrolase activity. The P. equi cinnamoyl ester hydrolase gene (estA) comprised an open reading frame of 1608 nt encoding a protein (EstA) of 536 amino acids and 55540 Da. EstA was modular in structure and comprised three distinct domains. The N-terminal domain was closely similar to a highly conserved non-catalytic 40-residue docking domain which is prevalent in cellulases and hemicellulases from three species of anaerobic fungi and binds to a putative scaffolding protein during assembly of the fungal cellulase complex. The second domain was also not required for esterase activity and appeared to be an atypically large linker comprising multiple tandem repeats of a 13-residue motif. The C-terminal 270 residues of EstA contained an esterase catalytic domain that exhibited overall homology with a small family of esterases, including acetylxylan esterase D (XYLD) from Pseudomonas fluorescens subsp. cellulosa and acetylxylan esterase from Aspergillus niger. This region also contained several smaller blocks of residues that displayed homology with domains tentatively identified as containing the essential catalytic residues of a larger group of serine hydrolases. A truncated variant of EstA, comprising the catalytic domain alone (EstA'), was expressed in Escherichia coli as a thioredoxin fusion protein and was purified to homogeneity. EstA' was active against synthetic and plant cell-wall-derived substrates, showed a marked preference for cleaving 1-->5 ester linkages between ferulic acid and arabinose in feruloylated arabino-xylo-oligosaccharides and was inhibited by the serine-specific protease inhibitor aminoethylbenzene-sulphonylfluoride. EstA' acted synergistically with xylanase to release more than 60% of the esterified ferulic acid from the arabinoxylan component of plant cell walls. Western analysis confirmed that EstA is produced by P. equi and is a component of the aggregated multienzyme cellulase-hemicellulase complex. Hybrid proteins, harbouring one, two or three iterations of the conserved 40-residue fungal docking domain fused to the reporter protein glutathione S-transferase, were produced. Western blot analysis of immobilized P. equi cellulase-hemicellulase complex demonstrated that each of the hybrid proteins bound to a 97 kDa polypeptide in the extracellular complex.

Activity of an Aspergillus terreus alpha-arabinofuranosidase on phenolic-substituted oligosaccharides

The effect of phenolic substitutions on the activity of an alpha-arabinofuranosidase from Aspergillus terreus was investigated using feruloylated oligosaccharides isolated from plant cell walls, equivalent oligosaccharides obtained through treatment with specific ferulic acid esterases, and a synthetic lignin-carbohydrate complex (LCC). Feruloyl substituents limited the hydrolysis of arabinoxylan and arabinan oligosaccharides but only if the feruloyl group was esterified to the terminal non-reducing arabinose. Somewhat surprisingly, the LCC-model compound, in which the arabinose residue is substituted with a bulky dilignol group, was degraded by the enzyme. This indicated that the enzyme is able to approach this linkage from the xylose side.

N alpha- and N epsilon-D-galacturonoyl-L-lysine amides: properties and possible occurrence in plant cell walls

Three representatives of a novel class of amide (isopeptide) glycoconjugates have been synthesised: N alpha-D-galacturonoyl-L-lysine and N epsilon-D-galacturonoyl-L-lysine and N epsilon-D-polygalacturonoyl-L-lysine. Galacturonoyl-lysine amide bonds were labile in 2 M trifluoroacetic acid at 120 degrees and in alkali, but relatively stable in cold acid. The amide bonds were resistant to digestion by Driselase, Pronase and trypsin. The polysaccharide backbone of N epsilon-D-polygalacturonoyl-L-lysine was hydrolysed by Driselase to yield two major ninhydrin-positive compounds which were shown by 1H and 13C NMR spectroscopy to be tri- and tetra-alpha-(1-->4)-D-galacturonoyl-L-lysines. To investigate the possible natural occurrence of N-galacturonoyl isopeptide bonds, we fed cell-suspension cultures of spinach and tomato with D-[6-14C]glucuronic acid, which radio-labels pectic polysaccharides. The radioactive cell walls were digested with, sequentially, Driselase, mild acid, and proteinases. On electrophoresis at pH 2.0, several of the radioactive digestion-products were cathodic. Some of the cathodic products yielded [14C]galacturonic acid upon complete acid hydrolysis. The existence of these products is compatible with the presence of novel N-galacturonoyl isopeptide bonds, which could serve as cross-links in plant cell walls.

Expression of antisense chalcone synthase RNA in transgenic hybrid walnut microcuttings. Effect on flavonoid content and rooting ability

Walnut somatic embryos (Juglans nigra x Juglans regia) were transformed with a vector containing a neomycin phosphotransferase II, a beta-glucuronidase and an antisense chalcone synthase (chs) gene. This antisense construct included a 400 bp cDNA fragment of a walnut chs gene under the control of the duplicated CaMV-35S promoter. Molecular, biochemical and biological characterizations were performed both on transformed embryos propagated by secondary somatic embryogenesis and on microshoots developed by in vitro culture of embryonic epicotyls from somatic embryos. Thirteen transformed lines with the vector containing the antisense chs gene, one line with only the gus and nptII genes and one untransformed line were maintained in tissue culture. Six of the antisense lines were shown to be flavonoid-deficient. They exhibited a strongly reduced expression of chs genes, very low chalcone synthase activity and no detectable amounts of quercitrin, myricitrin, flavane-3-ols and proanthocyanidins in stems. Rooting tests showed that decreased flavonoid content in stems of antisense chs transformed lines was associated with enhanced adventitious root formation. Free auxin and conjugated auxin contents were determined during the latter phase of the micropropagation, and no variations were detected between control and antisense chs transformed lines. The in vitro plants developed a large basal callus and apical necrosis upon auxinic induction and the transformed lines highly deficient in flavonoids were more sensitive to exogenous application of indolebutyric acid (IBA).

Xyloglucan endotransglycosylase: evidence for the existence of a relatively stable glycosyl-enzyme intermediate

Xyloglucan endotransglycosylases (XETs) catalyse the breakdown of xyloglucan molecules predominantly by transglycosylation. In this process, fragments of cleaved polysaccharide are preferentially transferred to other xyloglucan molecules or their oligosaccharide subunits, with overall retention of the anomeric configuration of the glycosidic bond. In accordance with the theory, we propose that the cleavage and re-formation of the glycosidic bond in xyloglucan involves the formation of a glycosyl-enzyme intermediate which decomposes by transfer of the glycosyl moiety to a suitable carbohydrate acceptor. XETs from nasturtium seed cotyledons, mung bean hypocotyls and cauliflower florets interacted with xyloglucan to form complexes of high Mr as judged by gel-permeation chromatography. The nasturtium enzyme also showed evidence of XET-xyloglucan complex-formation according to anion-exchange chromatography and adsorption of the complex to filter paper on the basis of affinity of its xyloglucan moiety for cellulose. The XET-xyloglucan complex was stable in water, 6 M urea and acidic and alkaline buffers (pH 2.5-9.5), but readily decomposed by transferring its glycosyl moiety to xyloglucan-derived oligosaccharides or by incubation with the strong nucleophile imidazole at pH 3.8-9.6. These results strongly support the assumption that XET forms a relatively stable covalently linked glycosyl-enzyme intermediate.

An Aspergillus awamori acetylesterase: purification of the enzyme, and cloning and sequencing of the gene

An inducible acetylesterase was purified from the culture medium of Aspergillus awamori strain IFO4033 growing on wheat-bran culture by ion-exchange, gel-filtration and hydrophobic-interaction chromatographies. The purified enzyme had an Mr of 31000 and contained Asn-linked oligosaccharides. The enzyme liberated acetic acid from wheat bran, hydrolysed only alpha-naphthyl acetate and propionate when aromatic esters were used for the substrate, and was tentatively classified as a carboxylic esterase (EC 3.1.1.1). The gene encoding acetylesterase was cloned and sequenced. The deduced amino acid sequence showed that acetylesterase was produced as a 304-amino-acid-residue precursor, which was converted post-translationally into a 275-amino-acid-residue mature protein. Part of the sequence of acetylesterase was similar to the region near the active-site serine of lipases of Geotrichum candidum and Candida cylindracea. A unique site of putative Asn-linked oligosaccharides was presented.

Digestion by fungal glycanases of arabinoxylans with different feruloylated side-chains

Alcohol-insoluble residues (AIRs) from Festuca and Zea cell cultures contained 7.4 and 35 nmol esterified ferulate mg-1, respectively. Driselase solubilised 79% of the feruloylated material from both AIRs. Of the feruloyl esters solubilised from Festuca and Zea AIRs, 72 and 56% respectively were small enough to be mobile on paper chromatography. The major feruloylated product of Zea AIR was the known 5-O-feruloyl-alpha-L-Araf-(1-->3)-beta-D-Xylp-(1-->4)- D-Xyl (Fer-Ara-Xyl-Xyl). In contrast, the smallest major feruloylated product of Festuca AIR was a feruloyl pentasaccharide (3) containing 3 Xyl, 1 Ara and 1 non-pentose residue (NPR). The Ara and two of the three Xyl groups of 3 were resistant to NaIO4. Mild acid hydrolysis of 3 gave xylobiose, a feruloyl trisaccharide and beta-D-Xylp-(1-->2)-(5-O-feruloyl)-L-Ara. Compound 3 was therefore NPR-(1-->3)-beta-D-Xylp-(1-->2)-(5-O-feruloyl)-alpha-L-Ar af-(1-->3)-beta-D-Xylp-(1-->4)-D-Xyl. We conclude that the complex feruloyl oligosaccharide side-chains of Festuca arabinoxylan do not protect the polysaccharide against hydrolysis by the fungal glycanases present in Driselase.

O-feruloylated, O-acetylated oligosaccharides as side-chains of grass xylans

Partial acid hydrolysis of cell wall material from Festuca arundinacea cell cultures yielded a novel O-feruloylated trisaccharide (3). Treatment of 3 with Driselase, which contains beta- but not alpha-D-xylosidase, released xylose plus the known compound, beta-D-xylopyranosyl-(1-->2)-(5-O-feruloyl)-L-arabinose. Since 3 contained one NaIO4-resistant xylose residue, it was concluded to be beta-D-xylopyranosyl-(1-->3)-beta-D-xylopyranosyl-(1--> 2)-(5-O-feruloyl)-L-arabinose. Partial acid hydrolysis of Festuca cell walls also yielded several higher-M(r) feruloylated oligosaccharides, including a feruloylated pentasaccharide, 4 (sugar composition: Ara + Xyl2 + two non-pentose residues) and a feruloylated heptasaccharide, 5 (Ara + Xyl3 + three non-pentose residues). Compounds 4 and 5 were endogenously O-acetylated but 3 was not. Similar or identical compounds were found in hydrolysates of 20 additional species of the Gramineae. These products represent a series of complex side-chains which, in vivo, are attached via Araf residues to the parent xylan. Their possible biological roles are discussed.

Release of ferulic acid from wheat bran by a ferulic acid esterase (FAE-III) from Aspergillus niger

Ferulic acid was efficiently released from a wheat bran preparation by a ferulic acid esterase from Aspergillus niger (FAE-III) when incubated together with a Trichoderma viride xylanase (a maximum of 95% total ferulic acid released after 5 h incubation). FAE-III by itself could release ferulic acid but at a level almost 24-fold lower than that obtained in the presence of the xylanase (2 U). Release of ferulic acid was proportional to the FAE-III concentration between 0.1 U and 1.3 U, but the presence of low levels of xylanase (0.1 U) increased the amount of ferulic acid released 6-fold. Total sugar release was not influenced by the action of FAE-III on the wheat bran, but the rate of release of the apparent end-products of xylanase action (xylose and xylobiose) was elevated by the presence of the esterase. The results show that FAE-III and the xylanase act together to break down feruloylated plant cell-wall polysaccharides to give a high yield of ferulic acid.

Hidden sources of galactose in the environment

A galactose-restricted diet free of lactose is lifesaving in patients with galactose-1-phosphate uridyl transferase (GALT) deficiency, but does not prevent long-term complications such as developmental delay, abnormal speech, poor growth and, in females, ovarian failure. Lactose, found in dairy products and as an extender in drugs, has been considered the primary source of galactose in the diet. Two recent publications reported that small amounts of galactose are present in many fruits and vegetables. We report the presence of considerable amounts of free galactose in some legumes (dried beans and peas) and the presence of bound galactose in many food plants. Galactose, in various glycosidic linkages, such as alpha-1,6, beta-1,3 and beta-1,4, and as a component of lipids, is ubiquitous in animals and plants. The bioavailability of alpha-1,6 and beta-1,3 linked galactose in foods is unknown. However, alpha-galactosidases found in plant and animal tissues may release galactose in alpha-1,6 linkage, and from diagalactosyldiacylglycerol. Galactose in beta-1,4 linkage and as monogalactosyldiacylglycerol may be released by beta-galactosidases in animal and plant tissues. Foods fermented by microorganisms for preparation or preservation purposes may contain free galactose. The role of free and bound galactose in cereals, fruits, legumes, nuts, organ meats, seeds, and vegetables in the poor outcome seen in some patients with GALT deficiency is unknown. It is certain that no patients with GALT deficiency have ever ingested a galactose-free diet.

Isolation and purification of feruloylated oligosaccharides from cell walls of sugar-beet pulp

Cell walls from sugar-beet pulp contain some feruloyl groups linked to the pectic neutral side-chains. Enzymic as well as chemical hydrolysis of the pulp yielded a series of feruloylated oligosaccharides, which have been purified by Sephadex LH-20 and Biogel P-2 chromatography in aqueous solvents. Feruloylated arabinose di-, tri-, hexa-, hepta-, and octa-saccharides as well as feruloylated galactose disaccharides were obtained after hydrolysis of the pulp with a mixture of fungal carbohydrases (Driselase). Feruloylated arabinose and galactose monosaccharides were obtained through mild acid hydrolyses. Both arabinose and galactose residues in the side-chains are feruloylated, 50-55% of the feruloyl groups being linked to arabinose residues and 45-50% to galactose residues. It is concluded that 1 out of 56 arabinose residues and 1 out of 16 galactose residues present as pectic side-chains in sugar-beet pulp carry a feruloyl group.

Sequencing of xyloglucan oligosaccharides by partial Driselase digestion: the preparation and quantitative and qualitative analysis of two new tetrasaccharides

The pentasaccharide (XXG), [formula: see text] obtained from Rosa xyloglucan, was converted to two isomeric tetrasaccharides, a and b (Xyl1.Glc3), by mild acid hydrolysis. During hydrolysis in 2 M trifluoroacetic acid at 90 degrees C, optimal yields of a and b were obtained after 20-40 min. Each tetrasaccharide was purified by preparative paper chromatography and high-pressure liquid chromatography (HPLC). The two isomers were distinguished by the products of their partial digestion with Driselase, which hydrolyses the glucosidic bonds sequentially from the non-reducing terminus: a and b yielded cellobiose and Xyl-->Glc-->Glc, respectively showing that they were [formula: see text] and [formula: see text] respectively. Tetrasaccharide b was chromatographically identical, upon HPLC on Dionex CarboPac PA1, with the tetrasaccharide produced from XXG by the action of Tropaeolum alpha-D-xylosidase, supporting the proposed structure. Xyloglucan oligosaccharides were assayed quantitatively by measurement of the yield of isoprimeverose (Xyl-->Glc) after complete Driselase digestion.

Degradation of feruloylated oligosaccharides from sugar-beet pulp and wheat bran by ferulic acid esterases from Aspergillus niger

The activity of two forms of ferulic acid esterase (FAE) from Aspergillus niger on a synthetic feruloylated substrate (methyl ferulate) and on 11 different feruloylated oligosaccharides from sugar-beet pulp and wheat bran was determined. The enzymes exhibited different specificities for the various feruloylated substrates and were more active on certain substrates of cell-wall origin than on methyl ferulate. Both enzymes preferred the arabinose residue to which ferulic acid is attached in the furanose form. FAE-I had no clear preference for the type of linkage involved between the ferulic acid units and the oligosaccharide chain. In contrast, FAE-III had a clear requirement for ferulic acid to be attached to O-5 of the Ara f ring while no catalysis was observed when ferulic acid was attached to O-2. Both enzymes showed maximum activity on feruloylated trisaccharides. An increase in the length of the oligosaccharide chain did not preclude catalysis, but feruloylated oligosaccharides of a dp > 3 were hydrolysed at a reduced rate. Our results support the hypothesis that different kinds of ferulic acid esterases exist with different specificities for the oligosaccharide chain of the feruloylated substrates.

Structure identification of feruloylated oligosaccharides from sugar-beet pulp by NMR spectroscopy

1D NMR (1H and 13C) and 2D NMR spectroscopy have been used to determine the structure of feruloylated oligosaccharides obtained by enzymic degradation or mild acid hydrolysis of sugar-beet pulp. Feruloylated oligosaccharides derived from pectic neutral side-chains containing arabinose or galactose residues were identified. In the feruloylated arabinose oligosaccharides, feruloyl groups were linked to O-2 of L-Ara f residues. The structure of the feruloylated arabinose disaccharide was identified as O-[2-O-(transferuloyl)-alpha-L-Ara f]-(1-->5)-L-Ara f and that of the feruloylated arabinose trisaccharide as O-alpha-L-Ara f-(1-->3)-O-[2-O-(trans-feruloyl)-alpha-L-Ara f]-(1-->5)-L- Ara f. The structure of the feruloylated galactose disaccharide was identified as O-[6-O-(trans-feruloyl) -beta-D-Gal p]-(1-->4)-D-Gal p. From our results, we suggest that the feruloyl groups present in sugar-beet pulp are linked to the arabinofuranosyl residues of the main core of alpha-(1-->5)-linked arabinan chains and to the galactopyranosyl residues of the main core of beta-(1-->4)-linked type I galactan chains.

Novel O-D-galacturonoyl esters in the pectic polysaccharides of suspension-cultured plant cells

Driselase digestion of uronate-6-14C-labeled primary walls of cultured spinach (Spinacia oleracea L.) cells yielded about 18 novel uronate-containing compounds, most of which could be hydrolyzed by cold dilute alkali to yield oligo-[14C]galacturonides. One typical Driselase digestion product (compound 17) yielded alpha-(1-->4)-D-[14C]galacturonotriose(GalA3) upon very mild treatment with alkali (50% yield of GalA3 in 7.2 min at pH 11 and 25 degrees C). One of the three galacturonate residues in compound 17 was reducible to a galactose residue with sodium borohydride, indicating that that GalA residue was esterified, via its--COOH group, to a putative alcohol. Compound 17 had a higher mobility than GalA3 on paper chromatography, indicating that the putative alcohol was relatively nonpolar. The putative alcohol could not have been methanol because Driselase readily hydrolyzed mono-, di-, and trimethyl esters of GalA3 to yield free galacturonic acid. Another Driselase digestion product (compound 12) was a derivative of GalA3 that apparently possessed two nonpolar esterified substituents: one about as labile as in compound 17, and the other approximately 10 times more stable. Compounds 12 and 17 could not labeled by in vivo feeding of [U-14C]cinnamate, suggesting that they were not phenolic conjugates. Similar but chromatographically distinguishable uronate-14C-labeled esters were obtained by Driselase digestion of walls of cultured carrot (Daucus carota L.), Paul's Scarlet rose (Rosa sp.), and tall fescue (Festuca arundinacea Schreber) cells. In spinach, the novel compounds constituted about 5% of the total galacturonate residues of the cell wall. The observations suggest that pectic polysaccharides are linked, via O-D-galacturonoyl ester bonds, to relatively hydrophobic constituents of the primary cell wall. Their possible role in wall architecture is discussed.

Structural characterization of feruloyl oligosaccharides from spinach-leaf cell walls

Hydrolysis of spinach-leaf cell walls with Driselase (a fungal enzyme preparation) released two arabino-oligosaccharides and one galactobiose, each carrying a ferulic acid moiety. The oligosaccharides were characterized by NMR spectroscopy, methylation analysis, and FABMS. They were O-(2-O-trans-feruloyl-alpha-L-arabinofuranosyl)-(1-->5)-L-arabinof uranose, O-(6-O-trans-feruloyl-beta-D-galactopyranosyl)-(1-->4)-D-galactopy ranose, and O-alpha-L-arabinofuranosyl-(1-->3)-O-(2-O-trans-feruloyl-alpha-L-a rabino- furanosyl)-(1-->5)-L-arabinofuranose.

Characterization of the laser-induced blue, green and red fluorescence signatures of leaves of wheat and soybean grown under different irradiance

The blue, green and red fluorescence emission of green wheat (Triticum aestivum L. var. Rector) and soybean leaves (Glycine max L. var. Maple Arrow) as induced by UV light (nitrogen laser: 337 nm) was determined in a phytochamber and in plants grown in the field. The fluorescence emission spectra show a blue maximum near 450 nm, a green shoulder near 530 nm and the two red chlorophyll fluorescence maxima near 690 and 735 nm. The ratio of blue to red fluorescence, F450/F690, exhibited a clear correlation to the irradiance applied during the growth of the plants. In contrast, the chlorophyll fluorescence ratio, F690/F735, and the ratio of blue to green fluorescence, F450/F530, seem not to be or are only slightly influenced by the irradiance applied during plant growth. The blue fluorescence F450 only slightly decreased, whereas the red chlorophyll fluorescence decreased with increasing irradiance applied during growth of the plants. This, in turn, resulted in greatly increased values of the ratio, F450/F690, from 0.5 - 1.5 to 6.4 - 8.0. The decrease in the chlorophyll fluorescence with increasing irradiance seems to be caused by the accumulation of UV light absorbing substances in the epidermal layer which considerably reduces the UV laser light which passes through the epidermis and excites the chlorophyll fluorescence of the chloroplasts in the subepidermal mesophyll cells.

Esterases of xylan-degrading microorganisms: production, properties, and significance

This review focuses on the description of recently discovered esterase enzymes involved in xylan degradation (acetyl xylan, feruloyl, and p-coumaroyl esterases). The occurrence of these enzymes in various microorganisms, assays used for determination of their activity, induction and production on different substrates, interaction with other xylanolytic enzymes, mode of action, substrate specificity, and biochemical characteristics are presented. The nature of substrates on which acetyl xylan esterase, feruloyl, and p-coumaroyl esterase are active and their role in xylan hydrolysis is emphasized. The potential applications of xylan-debranching esterases are outlined and their significance to applied microbiology is discussed.

The preparation and susceptibility to hydrolysis of novel O-galacturonoyl derivatives of carbohydrates

D-Galacturonic acid or (1-->4)-alpha-D-galacturonan reacted in aqueous pyridine in the presence of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide with alcohols to yield esters. The alcohols that gave high yields of D-galacturonoyl derivatives were primary and included methanol, ethanol, 1-propanol, D-glucose, D-galactose, methyl beta-D-glucopyranoside, methyl beta-D-galactopyranoside, and cellulose. D-Galacturonic acid itself readily gave an O-D-galacturonoyl-D-glacturonic acid. The proposed structure of one compound, methyl 6-O-D-galacturonoyl-beta-D-glucopyranoside, was supported by 1H and 13C NMR data and the FAB mass-spectral data. Each ester was hydrolysed at pH 11 and 25 degrees C within 1 h. O-D-Galacturonoyl-D-glucose was considerably more alkali labile than O-polygalacturonoyl-D-glucose, and O-D-galacturonoylcellulose had an intermediate stability. The esters were relatively stable to cold acid, but could be hydrolysed by M trifluoroacetic acid at 100 degrees C for 1 h. The esters tested were resistant to digestion by 'Driselase', although the glycosidic bonds of O-polygalacturonoyl-D-glucose were hydrolysed to yield O-oligogalacturonoyl-D-glucoses of low molecular weight. The possible application of these analytical methods to the detection of O-uronoyl-type cross-links in cell-wall polysaccharides is discussed.

Uniformly 14C-labelled plant cell walls: production, analysis and behaviour in rat gastrointestinal tract

Uniformly 14C-labelled primary cell walls (14C-PCW) were purified from suspension-cultured cells of spinach (Spinacia oleracea L.) grown in a medium containing D-[U-14C]glucose. The approximate polymer composition of the 14C-PCW preparation (% total 14C) was homogalacturonan 30, rhamnogalacturonan 23, xyloglucan 10, other hemicelluloses 3, cellulose 21, lignin 0, 14C-labelled protein < 3 and [14C]starch < 2. The degree of methyl esterification of the pectic polysaccharides was about 25%. The 14C-PCW contained about 4% O-acetyl and 3% non-volatile ester-linked residues. When tracer levels of these 14C-PCW were fed to rats, only about 18% of the 14C appeared in the faeces; negligible levels of 14C (0.07%) remained in the gut contents 4 d after feeding. Some 14C was present in the carcass. The results show that U-14C-labelled primary cell walls can be purified and radiochemically analysed by the methods developed here, and that primary cell walls are extensively fermented by the gut microflora of the rat.

Effect of cellulose synthesis inhibition on growth and the integration of xyloglucan into pea internode cell walls

2,6-Dichlorobenzonitrile (DCB, 100 mum) inhibited by 80 to 85% the incorporation of [(3)H]glucose into cellulose in stem segments of etiolated pea (Pisum sativum) seedlings. The inhibition lasted for at least 24 h. In the period 1 to 4 h after the excision of the segments, DCB did not influence elongation in the presence or absence of 2,4-dichlorophenoxyacetic acid (2,4-D). However, during the period 1 to 24 h after excision, DCB enhanced endogenous and 2,4-D-stimulated elongation by 65 and 34%, respectively. DCB did not affect the incorporation of (3)H from [(3)H]arabinose into xyloglucan, and did not change the ability of the [(3)H]xyloglucan formed in vivo to bind strongly to the cell wall. Therefore, at least 80 to 85% of newly synthesized cellulose was excess to the requirements for tight wall binding of newly synthesized xyloglucan. This conflicts with the hypothesis that xyloglucan is held in the cell wall solely by direct hydrogen bonding to the surfaces of cellulosic microfibrils.

Cytochrome c aided resolution of Lupinus albus isoperoxidases in a cathodal polyacrylamide gel electrophoresis system

In a cathodal polyacrylamide gel electrophoresis system, three distinct groups of isoperoxidases from Lupinus albus were found to achieve retention factors (rf) dependent on the quantity of sample applied onto the gel. The possibility of extract-derived substances weakly associating with peroxidase samples was investigated. Association of the putative agents survived dialysis against electrophoresis buffer with and without 2 M CaCl2 and freeze-thaw treatments. The addition of polyvinylpolypyrrolidone and polyethylene glycol to the homogenization buffer also proved ineffective in eliminating the variation in isoperoxidase rf although differences in the zymogram profiles of these samples were evident. The addition of spermine and cytochrome c to samples was found to increase the rf of some peroxidase bands. Electrophoresis of samples with cytochrome c resulted in the resolution of peroxidase groups to distinct bands at rf independent of the quantity of peroxidase applied. Control experiments indicate that this treatment did not introduce any detectable artifacts.

Endotransglycosylation of xyloglucans in plant cell suspension cultures

1. A xyloglucan-derived nonasaccharide ([3H]XG9; Glc4,Xyl3,Gal,Fuc) was neither taken up by cultured plant cells nor appreciably hydrolysed by them, but a proportion of it became incorporated into extracellular polymers in all cultures tested (Spinacia, Daucus, Rosa, Acer, Capsicum, Zea and Festuca). 2. In Spinacia these polymers were soluble in 20% (w/v) trichloroacetic acid, had apparent Mr 20,000-30,000, were able to bind reversibly to cellulose powder and were susceptible to hydrolysis by endo-beta-(1----4)-D-glucanase, indicating that they were xyloglucans. 3. The linkage formed between [3H]XG9 and the xyloglucan was alkali-stable and glucanase-labile, indicating that the reaction responsible for the incorporation was a transglycosylation. 4. The reducing terminus of the XG9 moiety remained reducing (convertible into [3H]glucitol by NaBH4) after incorporation into the polymer, showing that the XG9 was the glycosyl acceptor and the polysaccharide the donor. 5. The results provide the first evidence that polymeric xyloglucans are subject in vivo to cleavage followed by transfer of the cut end on the other xyloglucan-related molecules. 6. Similar endotransglycosylation reactions could occur within the primary cell wall, between pairs of high-Mr structural xyloglucan molecules. Such a reaction would provide a mechanism for reversible wall loosening and may thus be relevant to our understanding of plant cell growth.

Isolation and characterization of a diferuloyl arabinoxylan hexasaccharide from bamboo shoot cell-walls

Hydrolysis of bamboo shoot cell-walls with Driselase (a fungal enzyme preparation) released a diferuloyl arabinoxylan hexasaccharide. The structure of the diferuloyl oligosaccharide was determined to be 5,5'-di-O-diferul-9,9'-dioyl)-[alpha-L-arabinofuranosyl-(1-- --3)-O-beta-D-xylopyranosyl-(1----4)-D-xylopyranose] on the basis of n.m.r. spectroscopy, methylation analysis, and fast-atom-bombardment mass spectrometry (f.a.b.-m.s.). This is the first reported evidence that arabinoxylans are covalently cross-linked via diferulic acid.

Synthesis of methyl 5-O-trans-feruloyl-alpha-L-arabinofuranoside and its use as a substrate to assess feruloyl esterase activity

A synthetic scheme was developed for the production of methyl 5-O-trans-feruloyl-alpha-L-arabinofuranoside (FA-Ara) in gram quantities. This molecule accurately models the chemical attachment of ferulic acid to polysaccharides found in cell walls of plants in the Gramineae family. It is therefore a realistic substrate that can be used to monitor feruloyl esterase activity. Ultraviolet spectral analysis indicated that FA-Ara has an absorption maximum distinct from the hydrolytic product, ferulic acid (FA), over a wide range of solution pH values. The log molar extinction coefficient ranges from 4.16 to 4.36 for FA-Ara and 4.16 to 4.33 for FA depending upon the pH of the buffered solution. Consequently a convenient spectrophotometric assay can be utilized to monitor esterase activity. Three different methods were developed for using this model substrate to assess esterase activity, including thin-layer chromatography, a spectrophotometric assay, and the use of high-performance liquid chromatography.

Fruits and vegetables are a source of galactose: implications in planning the diets of patients with galactosaemia

It has become apparent that removing dairy products from the diets of patients with galactosaemia does not sufficiently diminish the deleterious signs. We have determined the amount of soluble monomeric galactose in 45 fruits and vegetables using capillary gas chromatography and selective ion monitoring. Galactose contents ranged from less than 0.1 mg per 100 g of tissue in artichoke, mushroom, olive, and peanut to 35.4 mg per 100 g in persimmon. Fruits and vegetables with over 10 mg per 100 g included date, papaya, bell pepper, tomato and watermelon. These results will provide important data for planning the diets of patients with galactosaemia.

Linkage of phenolic acids to cell-wall polysaccharides of bamboo shoot

Hydrolysis of bamboo shoot cell walls with Driselase (a fungal enzyme preparation) gave xyloglucan and arabinoxylan oligosaccharides containing ferulic and p-coumaric acids, respectively. The structures of two oligosaccharides containing phenolic acids are here determined to be O-(4-O-trans-feruloyl-alpha-D-xylopyranosyl)-(1----6)-D-glucopy rano se and O-[5-O-(trans-p-coumaroyl(-alpha-L-arabinofuranosyl]-(1----3)-O-be ta-D-xylopyranosyl-(1----4)-D-xylopyranose, on the basis of n.m.r. spectroscopy, methylation analysis, and f.a.b.-m.s. The possible role of phenolic acid substituents in cell-wall architecture is discussed.

Assay for trans-p-coumaroyl esterase using a specific substrate from plant cell walls

Cell walls of Coastal Bermuda grass (Cynodon dactylon) were treated with polysaccharide hydrolases to release O-[5-O-(trans-p-coumaroyl)-alpha-L-arabinofuranosyl]-(1----3)-O-be ta-D- xylopyranosyl-(1----4)-D-xylopyranose (PAXX) which was isolated by liquid chromatography. The isolated PAXX was greater than 95% pure as determined by 1H NMR and was used as substrate for a sensitive assay of trans-p-coumaroyl esterase. PAXX was hydrolyzed by culture filtrates from the anaerobic fungus Neocallimastix MC-2. The trans-p-coumaric acid released by enzymatic hydrolysis was assayed by reverse-phase HPLC, and as little as 100 ng of acid could be determined. Steady-state velocities for the release of the acid obeyed Michaelis-Menten kinetics. Vmax was determined to be 1.17 mumol min-1 mg-1 and Km 13.2 microM at pH 7.5 and 30 degrees C.