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1.
A Adkins 《Journal of industrial microbiology & biotechnology》1999,23(4-5):332-335
Sphingomonas paucimobilis , isolated from a soil in Manitoba, Canada, was able to utilize diclofop-methyl, (R,S)-methyl-2-[4-(2,4-dichlorophenoxy)phenoxy]propionate, as the sole source of carbon and energy. An actively growing aerobic
culture completely degraded 1.5 μg diclofop-methyl ml−1 to diclofop acid within 54 h, at 25°C. A biphasic growth pattern indicated that this organism was capable of degrading diclofop
acid to 4-(2,4-dichlorophenoxy)phenol and 2,4-dichlorophenol and/or phenol. The accumulation of 2,4-dichlorophenol in the
growth medium, however, suggested that Sphingomonas paucimobilis was unable to utilize this compound as a source of carbon and energy.
Received 26 April 1999/ Accepted in revised form 30 July 1999 相似文献
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Summary. The interaction of amino acids with the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was studied by charge-transfer chromatography
carried out on diatomaceous layers covered with different amount of 2,4-D and the effect of salts on the strength of interaction
was elucidated. It was established that Arg, His, Lys, Orn, Phe and Trp binds to 2,4-D, the binding process is of saturation
character. Principal component analysis proved that the concentration of 2,4-D exerts the highest impact on the interaction
and the effect of salts is of secondary importance. The results suggest that these amino acid residues may account for the
binding of 2,4-D to proteins and can play a considerable role in the detoxification processes by forming conjugates with 2,4-D.
Received April 10, 1998, Accepted September 15, 1998 相似文献
4.
Abscisic acid and hydraulic conductivity of maize roots: a study using cell- and root-pressure probes 总被引:31,自引:0,他引:31
Using root- and cell-pressure probes, the effects of the stress hormone abscisic acid (ABA) on the water-transport properties
of maize roots (Zea mays L.) were examined in order to work out dose and time responses for root hydraulic conductivity. Abscisic acid applied at
concentrations of 100–1,000 nM increased the hydraulic conductivity of excised maize roots both at the organ (root Lpr: factor of 3–4) and the root cell level (cell Lp: factor of 7–27). Effects on the root cortical cells were more pronounced
than at the organ level. From the results it was concluded that ABA acts at the plasmalemma, presumably by an interaction
with water channels. Abscisic acid therefore facilitated the cell-to-cell component of transport of water across the root
cylinder. Effects on cell Lp were transient and highly specific for the undissociated (+)-cis-trans-ABA. The stress hormone ABA facilitates water uptake into roots as soils start drying, especially under non-transpiring conditions,
when the apoplastic path of water transport is largely excluded.
Received: 26 February 2000 / Accepted: 17 August 2000 相似文献
5.
Summary. Due to the similarity in transport characteristics of polyamines and the y+ basic amino acid system, we hypothesized that both substrates could be moving through a common carrier site. Competitive
and cross inhibition experiments in intestinal epithelial cells revealed the possibility of a common transport site. N-ethylmalemide
(NEM) inhibited both lysine and putrescine transport, confirming that both were carried by a y+ transporter. Overexpressing the y+ transporter CAT-1 in a polyamine transport-deficient cell line, CHO-MG, did not reconstitute polyamine-transport. Thus, polyamines
are not traveling through CAT-1. To determine if lysine is carried by a polyamine transport site, an antizyme-overexpressing
cell line was used. Antizyme overexpression decreased polyamine uptake by 50%; in contrast, lysine transport was unaffected.
Therefore, lysine is not traveling through a polyamine transport site. It appears that polyamines and lysine are likely traveling
through a common unknown y+ transport site. 相似文献
6.
Apoplastic transport of abscisic acid through roots of maize: effect of the exodermis 总被引:22,自引:0,他引:22
The exodermal layers that are formed in maize roots during aeroponic culture were investigated with respect to the radial
transport of cis-abscisic acid (ABA). The decrease in root hydraulic conductivity (Lpr) of aeroponically grown roots was stimulated 1.5-fold by ABA (500 nM), reaching Lpr values of roots lacking an exodermis. Similar to water, the radial flow of ABA through roots (JABA) and ABA uptake into root tissue were reduced by a factor of about three as a result of the existence of an exodermis. Thus,
due to the cooperation between water and solute transport the development of the ABA signal in the xylem was not affected.
This resulted in unchanged reflection coeffcients for roots grown hydroponically and aeroponically. Despite the well-accepted
barrier properties of exodermal layers, it is concluded that the endodermis was the more effective filter for ABA. Owing to
concentration polarisation effects, ABA may accumulate in front of the endodermal layer, a process which, for both roots possessing
and lacking an exodermis, would tend to increase solvent drag and hence ABA movement into the xylem sap at increased water
flow (JVr). This may account for the higher ABA concentrations found in the xylem at greater pressure difference.
Received: 26 January 1999 / Accepted: 26 May 1999 相似文献
7.
Summary. The synthesis of an orthogonally protected constrained analogue of dipeptide DG (Asp-Gly) is reported exploiting alkylation
of a chiral lactam. The versatility of this analogue was proven by removal of t-Boc protecting group, followed by coupling under homogeneous conditions with t-Boc-Arg(Z2)-Gly, to give a conformationally restricted analogue of RGDG tetrapeptide.
Authors’ address: Mario Orena, Dipartimento di Scienze e Tecnologie Chimiche, Università Politecnica delle Marche, Via Brecce
Bianche, I-60131 Ancona, Italy 相似文献
8.
Analysis of the mechanistic basis by which sodium-coupled transport systems respond to changes in membrane potential is inherently
complex. Algebraic expressions for the primary kinetic parameters (K
m
and V
max
) consist of multiple terms that encompass most rate constants in the transport cycle. Even for a relatively simple cotransport
system such as the Na+/alanine cotransporter in LLC-PK1 cells (1:1 Na+ to substrate coupling, and an ordered binding sequence), the algebraic expressions for K
m
for either substrate includes ten of the twelve rate constants necessary for modeling the full transport cycle. We show here
that the expression of K
m
of the first-bound substrate (Na+) simplifies markedly if the second-bound substrate (alanine) is held at a low concentration so that its' binding becomes
the rate limiting step. Under these conditions, the expression for the K
Na
m
includes rate constants for only two steps in the full cycle: (i) binding/dissociation of Na+, and (ii) conformational `translocation' of the substrate-free protein. The influence of imposed changes in membrane potential
on the apparent K
Na
m
for the LLC-PK1 alanine cotransporter at low alanine thus provides insight to potential dependence at these sites. The data show no potential
dependence for K
Na
m
at 5 μm alanine, despite marked potential dependence at 2 mm alanine when the full algebraic expression applies. The results suggest that neither translocation of the substrate-free
form of the transporter nor binding/dissociation of extracellular sodium are potential dependent events for this transport
system.
Received: 10 April 1998/Revised: 6 July 1998 相似文献
9.
Photoassimilates are used by plants for production of energy, as carbon skeletons and in transport of fixed carbon between
different plant organs. Many studies have been devoted to characterizing the factors that regulate photoassimilate concentrations
in different plant species. Most studies examining photoassimilate concentrations in C3 plants have focused on analyzing starch and soluble sugars. However, work presented here demonstrates that a number of C3 plants, including the popular model organism Arabidopsis thaliana (L.) Heynh., and agriculturally important plants, such as soybean, Glycine max (L.) Merr., contain significant quantities of fumaric acid. In fact, fumaric acid can accumulate to levels of several milligrams
per gram fresh weight in Arabidopsis leaves, often exceeding those of starch and soluble sugars. Fumaric acid is a component of the tricarboxylic acid cycle and,
like starch and soluble sugars, can be metabolized to yield energy and carbon skeletons for production of other compounds.
Fumaric acid concentrations increase with plant age and light intensity in Arabidopsis leaves. Moreover, Arabidopsis phloem exudates contain significant quantities of fumaric acid, raising the possibility that fumaric acid may function in
carbon transport.
Received: 11 February 2000 / Accepted: 1 April 2000 相似文献
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Baran H 《Amino acids》2006,31(3):303-307
Summary. The aim of the study was to investigate the changes of taurine in the kainic acid (KA, 10 mg/kg, s.c.) chronic model of epilepsy,
six months after KA application. The KA-rats used were divided into a group of animals showing weak behavioural response to
KA (WDS, rare focal convulsion; rating scale <2 up to 3 h after KA injection) and a group of strong response to KA (WDS, seizures;
rating >3 up to 3 h after KA injection). The brain regions investigated were caudate nucleus, substantia nigra, septum, hippocampus,
amygdala/piriform cortex, and frontal, parietal, temporal and occipital cortices. KA-rats with rating <2 developed spontaneous
WDS which occurred chronically and six months after KA injection increased taurine levels were found in the hippocampus (125.4%
of control). KA-rats with rating >3 developed spontaneous recurrent seizures and six months after injection increased taurine
levels were found in the caudate nucleus (162.5% of control) and hippocampus (126.6% of control), while reduced taurine levels
were seen in the septum (78.2% of control). In summary, increased taurine levels in the hippocampus may involve processes
for membrane stabilisation, thus favouring recovery after neuronal hyperactivity. The increased taurine levels in the caudate
nucleus could be involved in the modulation of spontaneous recurrent seizure activity. 相似文献
13.
Fungi have evolved a unique α-aminoadipate pathway for lysine biosynthesis. The fungal-specific enzyme homoaconitate hydratase
from this pathway is moderately similar to the aconitase-family proteins from a diverse array of taxonomic groups, which have
varying modes of obtaining lysine. We have used the similarity of homoaconitate hydratase to isopropylmalate isomerase (serving
in leucine biosynthesis), aconitase (from the tricarboxylic acid cycle), and iron-responsive element binding proteins (cytosolic
aconitase) from fungi and other eukaryotes, eubacteria, and archaea to evaluate possible evolutionary scenarios for the origin
of this pathway. Refined sequence alignments show that aconitase active site residues are highly conserved in each of the
enzymes, and intervening sequence sites are quite dissimilar. This pattern suggests strong purifying selection has acted to
preserve the aconitase active site residues for a common catalytic mechanism; numerous other substitutions occur due to adaptive
evolution or simply lack of functional constraint. We hypothesize that the similarities are the remnants of an ancestral gene
duplication, which may not have occurred within the fungal lineage. Maximum likelihood, neighbor joining, and maximum parsimony
phylogenetic comparisons show that the α-aminoadipate pathway enzyme is an outgroup to all aconitase family proteins for which
sequence is currently available.
Received: 7 October 1997 相似文献
14.
Summary. Glucocorticoid hormones enhance the reabsorptive capacity of filtered amino acids in rat kidney, as it was shown in previous
in vivo clearance experiments. In the present study, the site of glucocorticoid action on neutral amino acid transport in superficial
nephrons of rat kidney was investigated using in vivo micropuncture technique. Adult female Wistar rats were treated with dexamethasone (DEX), and fractional excretion of L-glutamine
(L-Gln) and L-leucine (L-Leu) were determined and related to inulin after microinfusion into different nephron segments. DEX
reduced fractional excretion of both neutral amino acids as a sign of enhanced reabsorptive capacity. The site of main DEX
action on L-Leu reabsorption has been localized in the proximal straight tubule. However, in the case of L-Gln, the inhibition
of γ-glutamyltranspeptidase (γ-GT) by administration of acivicin indicated the importance of this brush border enzyme in reduced L-Gln excretion. DEX enhanced
γ-GT activity by tubular acidification. It can be presumed a DEX-inducible transport system for neutral amino acids mainly
localized in proximal straight tubules of rat kidney.
Received July 8, 1999 相似文献
15.
Summary. Vitamin C is accumulated in mammalian cells by two types of proteins: sodium-ascorbate co-transporters (SVCTs) and hexose
transporters (GLUTs); in particular, SVCTs actively import ascorbate, the reduced form of this vitamin.
SVCTs are surface glycoproteins encoded by two different genes, very similar in structure. They show distinct tissue distribution
and functional characteristics, which indicate different physiological roles. SVCT1 is involved in whole-body homeostasis
of vitamin C, while SVCT2 protects metabolically active cells against oxidative stress. Regulation at mRNA or protein level
may serve for preferential accumulation of ascorbic acid at sites where it is needed.
This review will summarize the present knowledge on structure, function and regulation of the SVCT transporters. Understanding
the physiological role of SVCT1 and SVCT2 may lead to develop new therapeutic strategies to control intracellular vitamin
C content or to promote tissue-specific delivery of vitamin C-drug conjugates.
Authors’ address: Dr. Isabella Savini, Department of Experimental Medicine and Biochemical Sciences, University of Rome Tor
Vergata, Via Montpellier 1, 00133 Rome, Italy 相似文献
16.
Synthesis of peptides employing Fmoc-/Boc-/Z-amino acid fluorides and activated commercial zinc dust
Suresh Babu Vommina V. Ananda Kuppanna 《International journal of peptide research and therapeutics》2000,7(1):41-46
Summary The coupling of urethane protected amino acid fluorides is accomplished in the presence of activated, commercial zinc dust
to synthesize several di- and tripeptides. The coupling was fast and racemization free. The yield as well as purity of the
peptides was satisfactory. The method was extended for the incorporation of sterically hindered α,α-dialkylamino acids and
N-methylamino acids as well. 相似文献
17.
Summary. The proton coupled amino acid transporter PAT1 expressed in intestine, brain, and other organs accepts L- and D-proline, glycine,
and L-alanine but also pharmaceutically active amino acid derivatives such as 3-amino-1-propanesulfonic acid, L-azetidine-2-carboxylic
acid, and cis-4-hydroxy-D-proline as substrates. We systematically analyzed the structural requirements for PAT1 substrates
by testing 87 amino acids, proline homologs, indoles, and derivatives. Affinity data and effects on membrane potential were
determined using Caco-2 cells. For aliphatic amino acids, a blocked carboxyl group, the distance between amino and carboxyl
group, and the position of the hydroxyl group are affinity limiting factors. Methylation of the amino group enhances substrate
affinity. Hetero atoms in the proline template are well tolerated. Aromatic α-amino acids display low affinity. PAT1 interacts
strongly with heterocyclic aromatic acids containing an indole scaffold. The structural requirements of PAT1 substrates elucidated
in this study will be useful for the development of prodrugs. 相似文献
18.
Summary. Fatty acid amide hydrolase (FAAH), a membrane-anchored enzyme responsible for the termination of endocannabinoid signalling,
is an attractive target for treating conditions such as pain and anxiety. Inhibitors of the enzyme, optimized using rodent
FAAH, are known but their pharmacology and medicinal chemistry properties on the human FAAH are missing. Therefore recombinant
human enzyme would represent a powerful tool to evaluate new drug candidates. However, the production of high amounts of enzyme
is hampered by the known refractiveness of FAAH to overexpression. Here, we report the successful overexpression of rat and
human FAAH as a fusion to the E. coli maltose-binding protein, retaining catalytic properties of native FAAH. Several known FAAH inhibitors were tested and differences
in their potencies toward the human and rat FAAH were found, underscoring the importance of using a human FAAH in the development
of inhibitors.
Authors’ address: Didier M. Lambert, Unité de Chimie pharmaceutique et de Radiopharmacie, Université catholique de Louvain,
Avenue E. Mounier 73.40, 1200 Bruxelles, Belgique 相似文献
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Control of seed dormancy in Nicotiana plumbaginifolia: post-imbibition abscisic acid synthesis imposes dormancy maintenance 总被引:13,自引:0,他引:13
The physiological characteristics of seed dormancy in Nicotiana plumbaginifolia Viv. are described. The level of seed dormancy is defined by the delay in seed germination (i.e the time required prior to
germination) under favourable environmental conditions. A wild-type line shows a clear primary dormancy, which is suppressed
by afterripening, whereas an abscisic acid (ABA)-deficient mutant shows a non-dormant phenotype. We have investigated the
role of ABA and gibberellic acid (GA3) in the control of dormancy maintenance or breakage during imbibition in suitable conditions. It was found that fluridone,
a carotenoid biosynthesis inhibitor, is almost as efficient as GA3 in breaking dormancy. Dry dormant seeds contained more ABA than dry afterripened seeds and, during early imbibition, there
was an accumulation of ABA in dormant seeds, but not in afterripened seeds. In addition, fluridone and exogenous GA3 inhibited the accumulation of ABA in imbibed dormant seeds. This reveals an important role for ABA synthesis in dormancy
maintenance in imbibed seeds.
Received: 31 December 1998 / Accepted: 9 July 1999 相似文献