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Markus Windwarder Rudolf FiglElisabeth Svehla Réka Tünde MócsaiJean-Baptiste Farcet Erika StaudacherPaul Kosma Friedrich Altmann 《Analytical biochemistry》2016
Analysis of the monosaccharides of complex carbohydrates is often performed by liquid chromatography with fluorescence detection. Unfortunately, methylated sugars, unusual amino- or deoxysugars and incomplete hydrolysis can lead to erroneous assignments of peaks. Here, we demonstrate that a volatile buffer system is suitable for the separation of anthranilic acid labeled sugars. It allows off-line examination of peaks by electrospray mass spectrometry. Approaches towards on-line mass spectrometric detection using reversed-phase or porous graphitic carbon columns fell short of achieving sufficient separation of the relevant isobaric sugars. Adequate chromatographic performance for isomeric sugars was achieved with reversed-phase chromatography of “hyper”-methylated anthranilic acid-labeled monosaccharides. Deuteromethyl iodide facilitates the discovery of naturally methylated sugars and identification of their parent monosaccharide as demonstrated with N-glycans of the snail Achatina fulica, where two thirds of the galactoses and a quarter of the mannoses were methylated. 相似文献
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Chen F Srinivasa Reddy MS Temple S Jackson L Shadle G Dixon RA 《The Plant journal : for cell and molecular biology》2006,48(1):113-124
Genes encoding seven enzymes of the monolignol pathway were independently downregulated in alfalfa (Medicago sativa) using antisense and/or RNA interference. In each case, total flux into lignin was reduced, with the largest effects arising from the downregulation of earlier enzymes in the pathway. The downregulation of l-phenylalanine ammonia-lyase, 4-coumarate 3-hydroxylase, hydroxycinnamoyl CoA quinate/shikimate hydroxycinnamoyl transferase, ferulate 5-hydroxylase or caffeic acid 3-O-methyltransferase resulted in compositional changes in lignin and wall-bound hydroxycinnamic acids consistent with the current models of the monolignol pathway. However, downregulating caffeoyl CoA 3-O-methyltransferase neither reduced syringyl (S) lignin units nor wall-bound ferulate, inconsistent with a role for this enzyme in 3-O-methylation ofS monolignol precursors and hydroxycinnamic acids. Paradoxically, lignin composition differed in plants downregulated in either cinnamate 4-hydroxylase or phenylalanine ammonia-lyase. No changes in the levels of acylated flavonoids were observed in the various transgenic lines. The current model for monolignol and ferulate biosynthesis appears to be an over-simplification, at least in alfalfa, and additional enzymes may be needed for the 3-O-methylation reactions of S lignin and ferulate biosynthesis. 相似文献
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Lemańska K van der Woude H Szymusiak H Boersma MG Gliszczyńska-Swigło A Rietjens IM Tyrakowska B 《Free radical research》2004,38(6):639-647
The biological effect of flavonoids can be modulated in vivo due to metabolism. The O-methylation of the catechol group in the molecule by catechol O-methyl transferase is one of the important metabolic pathways of flavonoids. In the present study, the consequences of catechol O-methylation for the pH-dependent radical scavenging properties of quercetin and luteolin were characterized both experimentally and theoretically. Comparison of the pKa values to the pH-dependent TEAC profiles reveals that O-methylation not only affects the TEAC as such but also modulates the effect of changing pH on this radical scavenging activity due to an effect on the pKa for deprotonation. The pH-dependent TEAC curves and computer calculated electronic parameters: bond dissociation energy (BDE) and ionisation potential (IP) even indicate that O-methylation of the luteolin catechol group affects the radical scavenging potential only because it shifts the pKa for deprotonation. O-Methylation of the quercetin catechol moiety affects radical scavenging capacity by both an effect on the pKa, and also by an effect on the electron and hydrogen atom donating properties of the neutral (N) and the anionic (A) form of the molecule. Moreover, O-methylation of a catechol OH-group in quercetin and luteolin has a similar effect on their TEAC profiles and on calculated parameters as replacement of the OH-group by a hydrogen atom. Altogether, the results presented provide new mechanistic insight in the effect of catechol O-methylation on the radical scavenging characteristics of quercetin and luteolin. 相似文献
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Thomas Wunder Jens Marr S. Kremer Olov Sterner Heidrun Anke 《Archives of microbiology》1997,167(5):310-316
The metabolism of pyrene by Penicillium glabrum strain TW 9424, a strain isolated from a site contaminated with polycyclic aromatic hydrocarbons (PAHs) was investigated
in submerged cultures. The metabolites formed were identified as 1-hydroxypyrene, 1,6- and 1,8-dihydroxypyrene, 1,6- and 1,8-pyrenequinone,
and 1-pyrenyl sulfate. In addition, two new metabolites were isolated and identified by UV, 1H nuclear magnetic resonance, and mass spectroscopy as 1-methoxypyrene and 1,6-dimethoxypyrene. Experiments with [methyl-3H]S-adenosyl-l-methionine (SAM) revealed that SAM is the coenzyme that provides the methyl group for the methyltransferase involved. To
our knowledge, this is the first time that methoxylated metabolites of PAHs have been isolated from fungal cultures.
Received: 27 August 1996 / Accepted: 8 January 1997 相似文献
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