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1.
Background
Although plants are the main source of vitamin C in the human diet, we still have a limited understanding of how plants synthesise L-ascorbic acid (AsA) and what regulates its concentration in different plant tissues. In particular, the enormous variability in the vitamin C content of storage organs from different plants remains unexplained. Possible sources of AsA in plant storage organs include in situ synthesis and long-distance transport of AsA synthesised in other tissues via the phloem. In this paper we examine a third possibility, that of synthesis within the phloem. 相似文献2.
A. A. Markosyan L. A. Abelyan M. O. Adamyan Zh. I. Akopyan V. A. Abelyan 《Applied Biochemistry and Microbiology》2007,43(1):36-40
Cyclodextrin glucanotransferases (CGTs, EC 2.4.1.19) from mesophilic, thermophilic, and halophilic bacteria and maltase (EC 3.2.1.20) from the yeast Saccharomyces cerevisiae were used for transglycosylation of ascorbic acid with starch, maltodextrin, γ-cyclodextrin, and maltose. These compounds served as donors of glucosyl residues. CGT from thermophilic strains was shown to be the most potent in this respect (the degree of transglycosylation was as high as 60%). 相似文献
3.
L-Ascorbyl oleate and L-ascorbyl linoleate were synthesized by an immobilized lipase from Candida antarctica with yields of 38% and 44%, respectively. L-Ascorbyl oleate was stable in sterile culture medium over 12 h at 37 °C but L-ascorbyl linoleate degraded by 17%. Ascorbyl oleate had a better protective effect on human umbilical cord vein endothelial cells treated with H2O2 than of L-ascorbic acid-2-phosphate-6-palmitate (Asc2P6P).Revisions requested 21 July 2004/26 August 2004; Revisions received 20 August 2004/27 September 2004 相似文献
4.
Escherichia coliL-asparaginase, an antileukaemic agent in man1, inhibits in vitro mitogen or antigen-induced blastogenesis in man2,3 and in animals (M. Bennett, E. G. Mayhew and T. Han, unpublished data) and suppresses bone-marrow derived antibody precursor cells in the mouse4. We now report that another L-asparaginase preparation—from Erwinia carotovora—also possesses antileukaemic activity5,6 and has a more pronounced immunosuppressive effect on in vitro blastogenesis than the E. coli enzyme. 相似文献
5.
Ascorbate (AsA) plays a fundamental role in redox homeostasis in plants and animals, primarily by scavenging reactive oxygen
species. Three genes, representing diverse steps putatively involved in plant AsA biosynthesis pathways, were cloned and independently
expressed in Solanum lycopersicum (tomato) under the control of the CaMV 35S promoter. Yeast-derived GDP-mannose pyrophosphorylase (GMPase) and arabinono-1,4-lactone oxidase (ALO), as well as myo-inositol oxygenase 2 (MIOX2) from Arabidopsis thaliana, were targeted. Increases in GMPase activity were concomitant with increased AsA levels of up to 70% in leaves, 50% in green
fruit, and 35% in red fruit. Expression of ALO significantly pulled biosynthetic flux towards AsA in leaves and green fruit by up to 54 and 25%, respectively. Changes in
AsA content in plants transcribing the MIOX2 gene were inconsistent in different tissue. On the other hand, MIOX activity was strongly correlated with cell wall uronic
acid levels, suggesting that MIOX may be a useful tool for the manipulation of cell wall composition. In conclusion, the Smirnoff–Wheeler
pathway showed great promise as a target for biotechnological manipulation of ascorbate levels in tomato. 相似文献
6.
Trötschel C Kandirali S Diaz-Achirica P Meinhardt A Morbach S Krämer R Burkovski A 《Applied microbiology and biotechnology》2003,60(6):738-742
A screening procedure was established to identify Corynebacterium glutamicum transposon mutants with an altered L-glutamate excretion behaviour. By this microtiter plate-based approach seven non- or less excreting C. glutamicum strains and two hyper-excreters were found. The subsequently carried out molecular analysis of a hyper-producing clone led to the identification of the gltS gene, which codes for the sodium-coupled secondary L-glutamate uptake system in C. glutamicum. Characterization of a gltS deletion strain revealed that this transporter has a weak but significant impact on L-glutamate production induced by biotin limitation in the wild type. Obviously, GltS leads to the re-uptake of excreted L-glutamate causing a futile cycle. In accord with this hypothesis, the overexpression of gltS decreased L-glutamate production. 相似文献
7.
The excretion of the aromatic amino acid l-tyrosine was achieved by manipulating three gene targets in the wild-type Escherichia coli K12: The feedback-inhibition-resistant (fbr) derivatives of aroG and tyrA were expressed on a low-copy-number vector, and the TyrR-mediated regulation of the aromatic amino acid biosynthesis was
eliminated by deleting the tyrR gene. The generation of this l-tyrosine producer, strain T1, was based only on the deregulation of the aromatic amino acid biosynthesis pathway, but no
structural genes in the genome were affected. A second tyrosine over-producing strain, E. coli T2, was generated considering the possible limitation of precursor substrates. To enhance the availability of the two precursor
substrates phosphoenolpyruvate and erythrose-4-phosphate, the ppsA and the tktA genes were over-expressed in the strain T1 background, increasing l-tyrosine production by 80% in 50-ml batch cultures. Fed-batch fermentations revealed that l-tyrosine production was tightly correlated with cell growth, exhibiting the maximum productivity at the end of the exponential
growth phase. The final l-tyrosine concentrations were 3.8 g/l for E. coli T1 and 9.7 g/l for E. coli T2 with a yield of l-tyrosine per glucose of 0.037 g/g (T1) and 0.102 g/g (T2), respectively. 相似文献
8.
Torres AM Tsampazi M Kennett EC Belov K Geraghty DP Bansal PS Alewood PF Kuchel PW 《Amino acids》2007,32(1):63-68
Summary. Platypus venom contains an isomerase that reversibly interconverts the second amino-acid residue in some peptides between
the L-form and the D-form. The enzyme acts on the natriuretic peptides OvCNPa and OvCNPb, and on the defensin-like peptides DLP-2 and DLP-4, but
it does not act on DLP-1. While the isomerization of DLP-2 to DLP-4 is inhibited by the amino-peptidase inhibitor amastatin,
it is not affected by the leucine amino-peptidase inhibitor bestatin. The enzyme, that is only present in minute quantities
in an extract of the venom gland, is thermally stable up to 55 °C, and it was found by anion-exchange chromatography to be
acidic. Isolation of the isomerase was carried out by combined ion-exchange chromatography and reverse-phase high performance
liquid chromatography (HPLC). 相似文献
9.
Lactobacillus casei was grown at 37 °C on sugarcane bagasse (5 g) soaked with cassava starch hydrolysate (final moistening volume 34 ml) containing
3 g reducing sugar in a solid-state condition. The maximum yield of l-lactic acid after various process optimisations was 2.9 g/5 g initial substrate corresponding to 97% conversion of sugar
to lactic acid with initial substrate moisture of 72%. 相似文献
10.
Zhu L Tao R Wang Y Jiang Y Lin X Yang Y Zheng H Jiang W Yang S 《Applied microbiology and biotechnology》2011,90(3):903-910
l-2-Aminobutyric acid can be synthesized in a transamination reaction from l-threonine and l-aspartic acid as substrates by the action of threonine deaminase and aromatic aminotransferase, but the by-product l-alanine was produced simultaneously. A small amount of l-alanine increased the complexity of the l-2-aminobutyric acid recovery process because of their extreme similarity in physical and chemical properties. Acetolactate
synthase has been introduced to remove the pyruvate intermediate for reducing the l-alanine concentration partially. To eliminate the remnant l-alanine, alanine racemase of Bacillus subtilis in combination with d-amino acid oxidase of Rhodotorula gracilis or Trigonopsis variabilis respectively was introduced into the reaction system for the l-2-aminobutyric acid synthesis. l-Alanine could be completely removed by the action of alanine racemase of B. subtilis and d-amino acid oxidase of R. gracilis; thereby, high-purity l-2-aminobutyric acid was achieved. The results revealed that alanine racemase could discriminate effectively between l-alanine and l-2-aminobutyric acid, and selectively catalyzed l-alanine to d-alanine reversibly. d-Amino acid oxidase then catalyzed d-alanine to pyruvate stereoselectively. Furthermore, this method was also successfully used to remove the by-product l-alanine in the production of other neutral amino acids such as l-tertiary leucine and l-valine, suggesting that multienzymatic whole-cell catalysis can be employed to provide high purity products. 相似文献
11.
A non-characterized gene, previously proposed as the d-tagatose-3-epimerase gene from Rhodobacter sphaeroides, was cloned and expressed in Escherichia coli. Its molecular mass was estimated to be 64 kDa with two identical subunits. The enzyme specificity was highest with d-fructose and decreased for other substrates in the order: d-tagatose, d-psicose, d-ribulose, d-xylulose and d-sorbose. Its activity was maximal at pH 9 and 40°C while being enhanced by Mn2+. At pH 9 and 40°C, 118 g d-psicose l−1 was produced from 700 g d-fructose l−1 after 3 h.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
12.
M. Helanto K. Kiviharju T. Granström M. Leisola A. Nyyssölä 《Applied microbiology and biotechnology》2009,83(1):77-83
l-Ribose is a rare and expensive sugar that can be used as a precursor for the production of l-nucleoside analogues, which are used as antiviral drugs. In this work, we describe a novel way of producing l-ribose from the readily available raw material l-arabinose. This was achieved by introducing l-ribose isomerase activity into l-ribulokinase-deficient Escherichia coli UP1110 and Lactobacillus plantarum BPT197 strains. The process for l-ribose production by resting cells was investigated. The initial l-ribose production rates at 39°C and pH 8 were 0.46 ± 0.01 g g−1 h−1 (1.84 ± 0.03 g l−1 h−1) and 0.27 ± 0.01 g g−1 h−1 (1.91 ± 0.1 g l−1 h−1) for E. coli and for L. plantarum, respectively. Conversions were around 20% at their highest in the experiments. Also partially purified protein precipitates
having both l-arabinose isomerase and l-ribose isomerase activity were successfully used for converting l-arabinose to l-ribose. 相似文献
13.
14.
15.
Daniel F. Austin 《Economic botany》2012,66(3):311-319
Book Reviews
Book Reviews Book Review Editor, Daniel F. Austin 相似文献16.
Campbell O. Webb 《Economic botany》2011,65(4):427-439
Book Reviews
Book Reviews Book Review Editor, Daniel F. Austin 相似文献17.
Circa 1900, a farmer from the eastern US planted 11 American chestnut (Castanea dentata) seeds on a newly established farm near West Salem in western Wisconsin. These trees were very successful, producing a large
stand of over 6,000 trees. Since this area is well outside the natural range of chestnut, these trees remained free from chestnut
blight until 1987. In the West Salem stand, chestnuts are the dominant species of a mixed forest community, reminiscent of
the chestnut–oak ecosystems of pre-1900 Appalachia. To identify putative mycorrhizal associates of chestnut in this unique
forest, our approach was twofold: (1) an extensive fruiting body survey was conducted for four seasons that yielded approximately
100 putative mycorrhizal species and (2) a belowground molecular approach was used to generate DNA sequences of the internal
transcribed spacer region from ectomycorrhizae. Unexpectedly, chestnut did not appear to be the dominant underground ectomycorrhizal-forming
plant species. This study highlights the need to identify the plant host species when conducting belowground molecular-based
surveys and provides preliminary identification of ectomycorrhizal fungi associated with a disjunct stand of American chestnut.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
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19.
Summary. Hydrogensquarates of dipeptide l-threonyl-l-serine (H-Thr-Ser-OH) and l-serine (HSq × Ser) have been synthesized, isolated and spectroscopic characterized by solid-state linear-polarized IR-spectroscopy, 1H- and 13C-NMR, ESI-MS and HPLC with tandem masspectrometry (MS-MS) methods. The structures of the salts and neutral dipeptide have
been predicted theoretically by ab initio calculations. In the case of H-Thr-Ser-OH the theoretical data are supported by IR-LD ones. The hydrogensquarates consist in positive charged dipeptide or amino acid
moiety and negative hydrogensquarate anion (HSq) stabilizing by strong intermolecular hydrogen bonds. The data about the l-serine hydrogensquarate are compared with known crystallographic data thus indicating a good correlation between the theoretical
predicted structures and experimentally obtained by single crystal X-ray diffraction. 相似文献
20.
l-arabinose isomerase (EC5.3.1.4. AI) mediates the isomerization of d-galactose into d-tagatose as well as the conversion of l-arabinose into l-ribulose. The AI from Lactobacillus plantarum SK-2 was purified to an apparent homogeneity giving a single band on SDS–PAGE with a molecular mass of 59.6 kDa. Optimum
activity was observed at 50°C and pH 7.0. The enzyme was stable at 50°C for 2 h and held between pH 4.5 and 8.5 for 1 h. AI
activity was stimulated by Mn2+, Fe3+, Fe2+, Ca2+ and inhibited by Cu2+, Ag+, Hg2+, Pb2+. d-galactose and l-arabinose as substrates were isomerized with high activity. l-arabitol was the strongest competitive inhibitor of AI. The apparent Michaelis–Menten constant (K
m), for galactose, was 119 mM. The first ten N-terminal amino acids of the enzyme were determined as MLSVPDYEFW, which is identical to L. plantarum (Q88S84). Using the purified AI, 390 mg tagatose could be converted from 1,000 mg galactose in 96 h, and this production
corresponds to a 39% equilibrium. 相似文献