Formation of [3H, 32P]phytic acid in germinating wheat

Doubly labeled phytic acid of high specific activity was prepared by incubating whole wheat seeds with [32P]phosphoric acid and [3H]myoinositol for 48 h and purifying by anion-exchange chromatography on AG 1- X 8 resin. Both degradation and synthesis of phytic acid were inhibited by KF to a similar extent, yet the catabolic and anabolic pathways involved distinctly different enzyme systems, as no [3H, 32P]myoinositol tetra- or pentaphosphate could be detected.     

Monoterpenol glycosides in plants and their biotechnological transformation

The present paper reviews the different monoterpenols and monoterpene polyols identified in the glycoside form in the plant kingdom. The glycosidic moieties involved are also considered. The natural pathways for the synthesis and hydrolysis of these monoterpene glycosides and the different hypothesis concerning their metabolism are discussed. The present state of different projects for the biotechnological transformation of these aromatic precursor compounds is reported.     

Novel enzymatic approach to the synthesis of flavonoid glycosides and their esters

Flavonoids such as (+)catechin can be efficiently solubilised in supersaturated solutions prepared with donor glycosides, e.g., p-nitrophenyl glycosides, di- and higher oligosaccharides, and poly(ethylene glycol) dimethyl ether in sufficiently high concentration for their efficient enzymatic glycosylation. Under these conditions several glycosidases readily accept (+)catechin as substrate and the target glycosides were prepared in one step in up to 26% yields. The regioselectivity of the reaction depends on the enzyme and substrate combination used; three positions, 5, 7, and 4', in the flavonoid can be glycosylated. The resulting and similar flavonoid glycosides were further modified by regioselective acylation with vinyl esters of arylpropenoic acids using lipases as biocatalyst. The efficiency of acylation was found to diminish in the order of vinyl cinnamate > vinyl ferulate > vinyl coumarate. This work demonstrates the feasibility of assembling complex flavonoid glycoside esters in just two steps by sequential use of commercially available glycosidases and lipases.     

Rational design,synthesis, and verification of affinity ligands to a protein surface cleft

The structure-based design, synthesis, and screening of a glucuronic acid scaffold library of affinity ligands directed toward the catalytic cleft on porcine pancreas alpha-amylase are presented. The design was based on the simulated docking to the enzyme active site of 53 aryl glycosides from the Available Chemicals Directory (ACD) selected by in silico screening. Twenty-three compounds were selected for synthesis and screened in solution for binding toward alpha-amylase using nuclear magnetic resonance techniques. The designed molecules include a handle outside of the binding site to allow their attachment to various surfaces with minimal loss of binding activity. After initial screening in solution, one affinity ligand was selected, immobilized to Sepharose (Amersham Biosciences), and evaluated as a chromatographic probe. A column packed with ligand-coupled Sepharose specifically retained the enzyme, which could be eluted by a known inhibitor.     

Cyanogenic glycosides and their metabolic enzymes in barley, in relation to nitrogen levels

The possible role for cyanogenic glycosides as nitrogen storage compounds was studied in barley, Hordeum vulgare (cv. Golf), cultivated under different nitrogen regimes. Cyanogenic glycosides were absent in seeds and roots but were synthesized in seedlings where they accumulated at a level of about 150 nmol shoot⁻¹ in control plants and 110 nmol shoot⁻¹ in nitrogen-starved plants. An enzyme involved in the breakdown of cyanogenic glycosides, β-glucosidase (EC 3.2.1.-) exhibited high activity in seeds and was also detected in roots and shoots. The activity of β-cyanoalanine synthase (EC 4.4.1.9), which is involved in the metabolism of HCN, was low in seeds but very high in roots and shoots. There was no correlation between the activities of the two enzymes and the content of cyanogenic glycosides or nitrogen. The relative content of nitrogen in cyanogenic glycosides never exceeded 0.3% of total nitrogen, and the amount of cyanogenic glycosides decreased at a low rate even at a stage when nitrogen limitation inhibited growth.     

The Effects of Compatible Solutes on the Heat Stability of Glutamine Synthetase from Chickpeas Grown under Different Nitrogen and Temperature Regimes

The activity of glutamine synthetase (GS) extracted from chickpeasgrown under different nitrogen and temperature regimes was examined.Cytosolic GS (GS₁) was much less temperature sensitive thanchloroplastic GS (GS₂). There was no change in the ratio ofthe two isoforms from plants with different growth temperatures.Specific activity of GS appeared to be independent of growthtemperature and was little affected by nitrogen supply. In vitro studies were performed on the heat stability of GS₂in the presence of glycine betaine, proline, and myoinositol.The latter was most effective in preventing loss of enzyme activityat high temperatures. Glycine betaine was also effective asa heat protectant but enzyme activity in the presence of prolinewas lower than the control at temperatures above 30 ?C. Theimportance of myo-inositol protection of metabolism is discussedin relation to the accumulation in chickpeas of another cyclitol,pinitol. Key words: Chickpeas, high temperature stress, glutamine synthetase     

Glycosylation of Phenolic Compounds by the Site-Mutated β-Galactosidase from Lactobacillus bulgaricus L3

β-Galactosidases can transfer the galactosyl from lactose or galactoside donors to various acceptors and thus are especially useful for the synthesis of important glycosides. However, these enzymes have limitations in the glycosylation of phenolic compounds that have many physiological functions. In this work, the β-galactosidase from Lactobacillus bulgaricus L3 was subjected to site-saturation mutagenesis at the W980 residue. The recombinant pET-21b plasmid carrying the enzyme gene was used as the template for mutation. The mutant plasmids were transformed into Escherichia coli cells for screening. One recombinant mutant, W980F, exhibited increased yield of glycoside when using hydroquinone as the screening acceptor. The enzyme was purified and the effects of the mutation on enzyme properties were determined in detail. It showed improved transglycosylation activity on novel phenolic acceptors besides hydroquinone. The yields of the glycosides produced from phenol, hydroquinone, and catechol were increased by 7.6% to 53.1%. Moreover, it generated 32.3% glycosides from the pyrogallol that could not be glycosylated by the wild-type enzyme. Chemical structures of these glycoside products were further determined by MS and NMR analysis. Thus, a series of novel phenolic galactosides were achieved by β-galactosidase for the first time. This was a breakthrough in the enzymatic galactosylation of the challenging phenolic compounds of great values.     

Effective chemoenzymatic synthesis of p-aminophenyl glycosides of sialyl N-acetyllactosaminide and analysis of their interactions with lectins

A convenient chemoenzymatic procedure for the synthesis of p-aminophenyl glycosides of sialyl N-acetyllactosaminide has been developed from p-nitrophenyl N-acetyl-beta-D-glucosaminide as starting material through three steps: synthesis of p-nitrophenyl N-acetyllactosaminide with beta-D-galactosidase, chemical reduction of the p-nitrophenyl group, and sialylation with sialyltransferase. The p-aminophenyl glycosides were then successfully biotin-labeled through the coupling with N-(+)-biotinyl-6-aminohexanoic acid to afford biotinylated oligosaccharides with an aminohexanosyl group and phenyl group as the spacers between the biotin and glycan. Furthermore, the biotin-labeled sugars were shown to be useful for immobilization and assay of the carbohydrate-lectin interactions by an optical biosensor based on surface plasmon resonance.     

Development of fecal microbial enzyme mix for mutagenicity assay of natural products

Orally administered herbal glycosides are metabolized to their hydrophobic compounds by intestinal microflora in the intestine of animals and human, not liver enzymes, and absorbed from the intestine to the blood. Of these metabolites, some, such as quercetin and kaempherol, are mutagenic. The fecal bacterial enzyme fraction (fecalase) of human or animals has been used for measuring the mutagenicity of dietary glycosides. However, the fecalase activity between individuals is significantly different and its preparation is laborious and odious. Therefore, we developed a fecal microbial enzyme mix (FM) usable in the Ames test to remediate the fluctuated reaction system activating natural glycosides to mutagens. We selected, cultured, and mixed 4 bacteria highly producing glycosidase activities based on a cell-free extract of feces (fecalase) from 100 healthy Korean volunteers. When the mutagenicities of rutin and methanol extract of the flos of Sophora japonica L. (SFME), of which the major constituent is rutin, towards Salmonella typhimurium strains TA 98, 100, 102, 1,535, and 1,537 were tested using FM and/or S9 mix, these agents were potently mutagenic. These mutagenicities using FM were not significantly different compared with those using Korean fecalase. SFME and rutin were potently mutagenic in the test when these were treated with fecalase or FM in the presence of S9 mix, followed by those treated with S9 mix alone and those with fecalase or FM. Freeze-dried FM was more stable in storage than fecalase. Based on these findings, FM could be usable instead of human fecalase in the Ames test.     

Sesquiterpene lactones and a myoinositol from glandular trichomes of Viguiera quinqueremis (Heliantheae; Asteraceae)

The extract of the floral parts of Viguiera quinqueremis afforded, in addition to known compounds, six new sesquiterpene lactones as well as a new myoinositol derivative. All compounds were detected in glandular trichomes which were collected micromechanically from the anther appendages and were analyzed by HPLC. Structure identification was performed by 1H NMR measurements including LC NMR and LC MS experiments.     

Efficient synthesis of alpha- and beta-chacotriosyl glycosides using appropriate donors, and their cytotoxic activity

Natural steroidal glycosides containing alpha-L-rhamnopyranosyl-(1-->4)-[alpha-L-rhamnopyranosyl-(1-->2)]-beta-D-glucopyranose (chacotriose) at the oligosaccharide moiety exhibit anti-cancer and anti-herpes activities. To investigate the structure-activity relationships of the aglycone parts of chacotriosides, we developed a synthesis method for chacotriosyl glycosides having various aglycones. In the process, it was revealed that alpha-chacotriosyl glycosides could be obtained mainly by using a trichloroacetimidate donor, while beta-chacotriosyl glycosides were afforded by using phosphite and phosphate donors. In cytotoxicity tests using the A549 and HepG2 cell lines, naturally occurring beta-chacotriosyl diosgenin and cholestanol exhibited higher activities than the corresponding alpha-chacotriosyl glycosides.     

The control of synthesis of bacterial cell walls. Interaction in the synthesis of nucleotide precursors

Phosphoenolpyruvate-UDP-N-acetylglucosamine enolpyruvyltransferase, UDP-N-acetylglucosamine pyrophosphorylase and CDP-glycerol pyrophosphorylase activities were demonstrated in soluble extracts from Bacillus licheniformis A.T.C.C. 9945. The effect of various nucleotides, sugar nucleotides and sugar phosphates on the nucleotide pyrophosphorylases was investigated. UDP-N-acetylglucosamine pyrophosphorylase was inhibited by UDP-MurAc-pentapeptide (UDP-N-acetylmuramyl-l-alanyl-d-glutamyl- meso-diaminopimelyl-d-alanyl -d-alanine) and CDP-glycerol. CDP-glycerol pyrophosphorylase was inhibited by UDP-MurAc-pentapeptide and stimulated by UDP-N-acetylglucosamine. Interaction between a precursor of one cell-wall polymer and an enzyme involved in the synthesis of a precursor of a second polymer has therefore been demonstrated. The possible role of such interaction in the control of bacterial cell-wall synthesis is discussed. Of the other compounds investigated mono- and di-nucleotides were shown to be inhibitory, indicating that nucleotide pyrophosphorylase activities may be influenced by the energy charge of the cell.     

Mechanism of cellulose synthesis in Agrobacterium tumefaciens.

Extracts of Agrobacterium tumefaciens incorporated UDP-[14C]glucose into cellulose. When the extracts were fractionated into membrane and soluble components, neither fraction was able to synthesize cellulose. A combination of the membrane and soluble fractions restored the activity found in the original extracts. Extracts of cellulose-minus mutants showed no significant incorporation of UDP-glucose into cellulose. When mixtures of the extracts were made, the mutants were found to fall into two groups: extracts of mutants from the first group could be combined with extracts of the second group to obtain cellulose synthesis. No synthesis was observed when extracts of mutants from the same group were mixed. The groups of mutants corresponded to the two operons identified in sequencing the cel genes (A. G. Matthysse, S. White, and R. Lightfoot. J. Bacteriol. 177:1069-1075, 1995). Extracts of mutants were fractionated into membrane and soluble components, and the fractions were mixed and assayed for the ability to synthesize cellulose. When the membrane fraction from mutants in the celDE operon was combined with the soluble fraction from mutants in the celABC operon, incorporation of UDP-glucose into cellulose was observed. In order to determine whether lipid-linked intermediates were involved in cellulose synthesis, permeablized cells were examined for the incorporation of UDP-[14C]glucose into material extractable with organic solvents. No radioactivity was found in the chloroform-methanol extract of mutants in the celDE operon, but radioactive material was recovered in the chloroform-methanol extract of mutants in the celABC operon. The saccharide component of these compounds was released after mild acid hydrolysis and was found to be mainly glucose for the celA insertion mutant and a mixture of cellobiose, cellotriose, and cellotetrose for the celB and celC insertion mutants. The radioactive compound extracted with chloroform-methanol form the celC insertion mutant was incorporated into cellulose by membrane preparations from celE mutants, which suggests that this compound is a lipid-linked intermediate in cellulose synthesis.     

Purification of cytosolic beta-glucosidase from pig liver and its reactivity towards flavonoid glycosides

Flavonoid glycosides are common dietary components which may have health-promoting activities. The metabolism of these compounds is thought to influence their bioactivity and uptake from the small intestine. It has been suggested that the enzyme cytosolic beta-glucosidase could deglycosylate certain flavonoid glycosides. To test this hypothesis, the enzyme was purified to homogeneity from pig liver for the first time. It was found to have a molecular weight (55 kDa) and specific activity (with p-nitrophenol glucoside) consistent with other mammalian cytosolic beta-glucosidases. The pure enzyme was indeed found to deglycosylate various flavonoid glycosides. Genistein 7-glucoside, daidzein 7-glucoside, apigenin 7-glucoside and naringenin 7-glucoside all acted as substrates, but we were unable to detect activity with naringenin 7-rhamnoglucoside. Quercetin 4'-glucoside was a substrate, but neither quercetin 3, 4'-diglucoside, quercetin 3-glucoside nor quercetin 3-rhamnoglucoside were deglycosylated. Estimates of K(m) ranged from 25 to 90 microM while those for V(max) were about 10% of that found with the standard artificial substrate p-nitrophenol glucoside. The non-substrate quercetin 3-glucoside was found to partially inhibit deglycosylation of quercetin 4'-glucoside, but it had no effect upon activity with p-nitrophenol glucoside. This study confirms that mammalian cytosolic beta-glucosidase can deglycosylate some, but not all, common dietary flavonoid glycosides. This enzyme may, therefore, be important in the metabolism of these compounds.     

Chemical constituents of Uncaria rhynchophylloides How and their chemotaxonomic significance

One undescribed 1,4-diazaindan-type alkaloid, namely howlumine (1), along with seventeen known compounds, including a known analogue, agrocybenine (2), three iridoid glycosides (3–5), four megastigmane glycosides (6–9), two benzoic acid derivatives (10–11), two phenylpropanoids (12–13), and five flavonoids (14–18), were isolated from the 95% EtOH extract of the aerial parts of Uncaria rhynchophylloides How. The structures of these compounds were elucidated by spectroscopic analyses. All compounds were isolated from this plant for the first time. Howlumine and agrocybenine represent the first report of 1,4-diazaindan-type alkaloids from the genus Uncaria. Furthermore, the chemotaxonomic significance of the isolates was also discussed.     

Enzymatic Synthesis of Polyol- and Masked Polyol- Glycosides using β-Glycosidase of Sulfolobus Solfataricus

The use of commercially available mesophilic glycosidases in the enzymatic synthesis of glycosides of different types is a well established method suffering from some drawbacks such as a poor yield. Substrates with three or four hydroxyl groups have been subjected to enzymatic glucosylation using crude homogenate of the thermophilic archaeon Sulfolobus solfataricus containing a β-glycosidase activity able to transfer glucose, galactose and fucose from different donors. The stereochemistry of this reaction was interpreted in terms of interaction with a possible “glucose” active site of the enzyme. In addition masked or protected derivatives of tetritols and some simple unsaturated alcohols were glycosylated yielding glycosides in yields very competitive with those obtained using mesophilic enzymes, examples of further chemical manipulation of these compounds were reported. When using a scarce amount of acceptor, a reasonable amount of products could be obtained by adding different aliquots of donor at time intervals.     

Plant-associated bacteria degrade defense chemicals and reduce their adverse effects on an insect defoliator

Phytophagous insects must contend with numerous secondary defense compounds that can adversely affect their growth and development. The gypsy moth (Lymantria dispar) is a polyphagous herbivore that encounters an extensive range of hosts and chemicals. We used this folivore and a primary component of aspen chemical defenses, namely, phenolic glycosides, to investigate if bacteria detoxify phytochemicals and benefit larvae. We conducted insect bioassays using bacteria enriched from environmental samples, analyses of the microbial community in the midguts of bioassay larvae, and in vitro phenolic glycoside metabolism assays. Inoculation with bacteria enhanced larval growth in the presence, but not absence, of phenolic glycosides in the artificial diet. This effect of bacteria on growth was observed only in larvae administered bacteria from aspen foliage. The resulting midgut community composition varied among the bacterial treatments. When phenolic glycosides were included in diet, the composition of midguts in larvae fed aspen bacteria was significantly altered. Phenolic glycosides increased population responses by bacteria that we found able to metabolize these compounds in liquid growth cultures. Several aspects of these results suggest that vectoring or pairwise symbiosis models are inadequate for understanding microbial mediation of plant–herbivore interactions in some systems. First, bacteria that most benefitted larvae were initially foliar residents, suggesting that toxin-degrading abilities of phyllosphere inhabitants indirectly benefit herbivores upon ingestion. Second, assays with single bacteria did not confer the benefits to larvae obtained with consortia, suggesting multi- and inter-microbial interactions are also involved. Our results show that bacteria mediate insect interactions with plant defenses but that these interactions are community specific and highly complex.     

Synthesis of 8-azidooctyl glycoside derivatives of the O-chain repeating unit of Escherichia coli O9a lipopolysaccharide and a methylated analog

Described is the synthesis of 8-azidooctyl glycoside derivatives of the Escherichia coli serotype O9a O-chain tetrasaccharide repeating unit and the terminal tetrasaccharide motif in this polysaccharide, which contains a methyl group on O-3 of the distal mannopyranose residue. The assembly of these compounds involved the sequential addition of monosaccharide residues from the reducing to the nonreducing end of the molecule using glycosyl trichloroacetimidate donors. Both compounds were initially prepared as p-methoxyphenyl glycosides, which were converted to the corresponding 8-azidooctyl derivatives at a late stage in the synthesis.     

Chromatin decondensation and DNA synthesis in human sperm activated in vitro by using Xenopus laevis egg extracts

An in vitro sperm activation system was used to study nuclear swelling-chromatin decondensation and DNA synthesis; processes that occur in vivo following fertilization. Lysolecithin-permeabilized human sperm were incubated in Xenopus laevis egg extract and examined by using phase-contrast light microscopy, electron microscopy, and autoradiography. During a 3-hour incubation, the activated sperm nuclear chromatin underwent a decondensation-recondensation cycle during which DNA was synthesized. This also occurred when egg extract was given a 3-hour preincubation before the addition of the sperm, suggesting that the factor(s) required for initiating the decondensation-recondensation cycle is associated with the sperm. Because both nuclear swelling and DNA synthesis were found to be reproducible and quantifiable, we studied the effect of various agents on the two processes, characterizing the critical component(s) in the egg extract that induces these events. EGTA was found to have no effect on the induced nuclear swelling or DNA synthesis that occurs in the activated sperm. Freezing and thawing the extract or treating the extract with aphidicolin also had no effect on subsequent nuclear swelling; however, the DNA synthesis activity was blocked. Sperm incubated in extract treated with alkaline phosphatase (AP) had both nuclear swelling and DNA synthesis blocked. However, if the sperm were pretreated with DTT, and then incubated with the AP-treated extract, only the DNA synthesis activity of the extract was blocked. When the extract was treated with serine protease inhibitors (PMSF, soybean trypsin inhibitor, or alpha-2-macroglobulin), nuclear swelling occurred; however, DNA synthesis was blocked. These data suggest that phosphoproteins are involved in one or more of the activation events and that a serine protease(s) is involved in the synthesis of DNA.     

Extracellular β-D-glucosidase of the Penicillium canescens marine fungus

Extracellular β-D-glucosidase was isolated in a homogeneous state from the Penicillium canescens marine fungus. According to SDS-electrophoresis, the molecular weight of the enzyme was 64 kDa and the maximal activity was observed at pH 5.2 and 70°C. Glucosidase catalyzed the hydrolysis of β-glycosidic bonds both in glycosides and in glucose disaccharides and had transglycosylation activity. The enzyme can be used for the deglycosylation of natural glycosides and in enzymatic synthesis of new carbohydrate—containing compounds.