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T W Fan

Publications and source records attributed to T W Fan.

24 records · Page 2Linked to original sources
PubMed1988

An in vivo 1H and 31P NMR investigation of the effect of nitrate on hypoxic metabolism in maize roots.

The effect of nitrate on the short-term hypoxic response and recovery of flooded mature maize roots has been investigated in vivo by 1H and 31P NMR and in vitro by 1H NMR and gas chromatography-mass spectrometry. Employing 1H NMR in addition to 31P NMR extended the number of identifiable compounds in vivo from 4 to 15, while in vitro two-dimensional NMR and gas chromatography-mass spectrometry aided rigorous in vivo 1H NMR resonance assignments and quantitation of 24 compounds. In the absence of nitrate, the concentrations of key metabolites including alanine, ethanol, gamma-aminobutyrate, lactate, succinate, and sucrose changed during 8 h of hypoxia in a manner consistent with reduced tricarboxylic acid cycle activity and diversion to glycolytic fermentation. The pH drop in the cytoplasm during hypoxia was rapid, about 0.2 unit, and diminished quickly upon recovery. Rapid recovery of ethanol, succinate, and sucrose levels was also observed, which indicates a return to normal aerobic metabolism. Although the hypoxic response itself, including pH, was not greatly affected by the presence of nitrate, nitrate reduced the amount of fermentation end products produced, helped maintain a higher free NTP concentration during hypoxia, and increased the rate of overall recovery from hypoxia. These findings suggest the presence of a nitrate-induced maintenance-level respiration in hypoxic maize roots, which helps explain the protection imparted by nitrate to flooded hypoxic maize plants.

Energy Transfer↗
PubMed1986

Combined use of 1H-NMR and GC-MS for metabolite monitoring and in vivo 1H-NMR assignments.

Thirty-three metabolites were observed in perchloric acid extracts of four different tissues by in vitro 1H-NMR, GC-MS and alcohol dehydrogenase assay, and the information was used to interpret an in vivo two-dimensional nuclear Overhauser effect 1H-NMR spectrum. The metabolite profiles of the different tissues indicate a number of potential tissue-specific markers: N-acetylaspartate and gamma-aminobutyric acid for rat brain, glutamine/glutamic acid ratio for dog heart, arginine and sucrose for carrot, and t-aconitate, sucrose, asparagine/aspartic acid concentration ratios for corn roots. gamma-Aminobutyric acid and malate can be regarded as metabolic indicators for stressed corn roots. Concentrations of threonine and valine in corn roots were constant under hypoxic and salt stress, and can serve as internal standards for both in vivo and in vitro NMR studies. The in vitro information was further used to identify 12 compounds from the in vivo 1H-NMR spectra (including the two-dimensional nuclear Overhauser effect spectrum) of a carrot cylinder by correlating the chemical shift and nuclear Overhauser effect information. Thus, our choice of methods with a capability for structural determination allows the characterization of complex tissue extracts with minimum sample preparation, and supports, as well as complements, in vivo 1H-NMR investigations of metabolism.

Animals↗
PubMed1986

Monitoring of hypoxic metabolism in superfused plant tissues by in vivo 1H NMR.

We have used a coaxial superfusion system to obtain physiologically interpretable in vivo 1H NMR spectra at 500 MHz of carrot roots, maize roots, and rice shoots in water (no 2H2O). The superfusion system was constructed from common laboratory parts, required no modification of the probe and sample loading procedure, and was inherently leak resistant. The assignment and quantitation of the in vivo 1H NMR resonances were achieved by performing two-dimensional NMR experiments in vivo, and by in vitro analysis including NMR and gas chromatography-mass spectrometry. The in vivo spectra were dominated by resonances arising from sugars, organic acids, amino acids, and ethanol. In vivo measurements of spin-lattice relaxation times and chemical shifts of beta protons of malate in carrot roots suggested that malate was located in a relatively viscous and acidic compartment. In rice shoots, the hypoxic time courses of 9 metabolites were established in vivo, and 23 in vitro. In both cases, accumulation of lactate, ethanol, Ala, and gamma-aminobutyrate as well as a decrease in Gln and Asn concentrations were observed. These findings are consistent with accelerated glycolysis and decreased tricarboxylic acid cycle activity.

Amino Acids↗
PubMed1985

Isolation and characterization of two cyanogenic beta-glucosidases from flax seeds.

Two cyanogenic beta-glucosidases, linustatinase and linamarase, were isolated and purified from flax seeds (Linum ussitatissimum). They catalyze the sequential hydrolysis of linustatin and neolinustatin to yield acetone and methylethyl ketone cyanohydrins, respectively. The purification procedure for linustatinase involved acetone extraction, precipitation by polyethyleneimine and ammonium sulfate (40-80% saturation), and Red A gel, concanavalin A-Sepharose, and PBE 94 column chromatography; that for linamarase was similar except that polyethyleneimine precipitation was eliminated and DE-52 and Sepharose CL-6B replaced Red A gel column chromatography. The native substrates neolinustatin and linamarin were used for the assay during purification. Both proteins were purified to electrophoretic homogeneity. Linustatinase is an alpha beta dimer (molecular weights of alpha and beta = 39,000 and 19,000, respectively) while linamarase appears to be an alpha 5 beta 5 decamer (molecular weights of alpha and beta = 62,500 and 65,000, respectively). Both enzymes contain mannose or glucose. Linustatinase exists in five different isozymic forms (isoelectric points between 7 and 8) whereas linamarase occurs in one major form (isoelectric point 4 to 5). The kinetic parameters of the two enzymes are similar: acidic pH optima, Km's in the millimolar range, and competitive inhibition by delta-gluconolactone, a transition state analog. The presence of an aglycone structure in the substrates is important for both enzyme activities. In addition, both enzymes are specific towards the beta-glycosidic linkage; linustatinase (a beta-bis-glucosidase) readily hydrolyzes beta-bis-glucosides with 1,6 and 1,3 linkages whereas linamarase (a beta-monoglucosidase) exhibits little activity towards these substrates.

Amygdalin↗
PubMedDate not supplied

Phytosiderophores influence on cadmium mobilization and uptake by wheat and barley plants.

A constant anthropogenic release of cadmium to the environment has resulted in a continuous buildup of Cd in soils. Uptake and accumulation of Cd in plant tissue and in grains may lead to food chain transfer to humans. Application of synthetic chelates was suggested to increase metal mobilization and facilitate phytoextraction as a means for the remediation of metal-polluted soils. However, most of the chelate-extracted metal may be leached rather than mobilized to plant roots. In contrast to the synthetic chelates added to soils, plant-produced chelators called phytosiderophores (PS) are excreted directly to the rhizosphere. Previous studies have shown that PS facilitate uptake of Zn and Fe by graminaceous plants. In this study, a two-step PS mediation of Cd uptake was hypothesized: (i) extraction and chelation in the soil solution, and (ii) delivery of the chelated Cd to the uptake system of the plant. We examined Cd extraction by PS, the synthetic chelate HEDTA [N-(2-hydroxyethyl)-ethylenediaminetriacetic acid], and a fungal siderophore rhizoferrin from solid-phase Cd phosphate at pH 7.3 with and without Fe competition in the presence of Ca and Mg as additional competing metals. While rhizoferrin did not extract Cd, PS and HEDTA did extract Cd even in the presence of Fe. Yet, uptake of Cd by wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) plants was not significantly influenced by Fe stress, but instead was controlled primarily by Cd2+ activity in solution. These results suggest that even though Cd may be mobilized by PS, there is no significant uptake of the Cd-PS complex by the plant roots.

Biological Availability↗