共查询到20条相似文献,搜索用时 15 毫秒
1.
Summary. It has been firmly established that excitatory amino acids (EAAs), such as glutamate, are pivotal elements in the hypothalamic
circuitry involved in the control of pituitary function. The actions of EAAs are mediated by different postsynaptic receptor
subtypes, which include N-methyl D-aspartate (NMDA), kainate (KA), 2-amino-3-hydroxy-5 methyl-4-isoxazol propionic acid (AMPA)
and metabotropic receptors. In this review, we summarize our experimental work on the role of EAA neurotransmission in the
control of GH secretion in the rat. Detailed characterization of the effects of agonists and antagonists of glutamate receptors
on GH release revealed that activation of NMDA, KA and AMPA receptors at different age-points resulted in clear-cut stimulation
of GH secretion, although age- and sex-dependent differences were detected in the pattern of response to the different agonists.
This stimulatory action was proven nitric oxide (NO)-dependent and not exerted at the pituitary level. In addition, evaluation
of the role of hypothalamic GH-releasing hormone (GHRH) in the stimulatory action of NMDA by means of immunoneutralization
of endogenous GHRH or destruction of GHRH producing neurons suggested the involvement of signals other than GHRH in this response.
Further, evidence was obtained on the modulation of the EAA system by gonadal factors, and on the physiological relevance
of EAA pathways in the regulation of pulsatile GH release. In conclusion, our data using the rat as animal model provide evidence
for a pivotal role of glutamate pathways in the regulation of GH secretion throughout the life-span.
Received May 5, 1999, Accepted July 28, 1999 相似文献
2.
Summary. A technique is described for the enantiomeric determination of L- and D-amino acids. It works on the principle that the separation
efficiency of high-performance liquid chromatography is coupled with the specificity of enzymes and the sensitivity of electrochemical
detection. After separation on a lithium cation-exchange column the amino acids are converted into keto acids and hydrogen
peroxide under catalyzation of L- or D-amino acid oxidase. Hydrogen peroxide is detected amperometrically. The method has
been tested by the analysis of beer, port, sherry, wine and fruit juice.
A main emphasis was put onto the determination of D-alanine which can serve as an indicator for bacterial contamination. It
is shown that a coupling of HPLC with enzyme reactors is a suitable technique for the rapid detection of this marker.
Received April 14, 1999, Accepted September 15, 1999 相似文献
3.
Summary. Accumulation of amino acids was studied in rice roots of 3-day-old seedlings subjected for 48 h to anaerobic conditions.
Alanine and Gaba were the main amino acids accumulated under anoxia. Their synthesis was strongly inhibited by MSX and AZA,
inhibitors of glutamine synthetase and glutamate synthase. These activities increased after 8 h of anaerobic treatment and,
by immunoprecipitation of 35S-labeled proteins, it was shown that glutamine synthetase and ferredoxin-dependent glutamate synthase were synthesized during
the treatment. These findings indicate that the glutamine synthetase/glutamate synthase cycle play an important role in anaerobic
amino acid accumulation.
Received April 5, 1999 相似文献
4.
Summary. The lancelet (amphioxus), a cephalochordate, is the closest invertebrate relative to vertebrates, with a simple vertebrate-like
body plan and a prototypical genome. We have determined D-aspartic acid (D-Asp) and major free L-amino acids (L-AAs) content
in the nervous system (neural tube) of the European amphioxus Branchiostoma lanceolatum, and have compared these values with those of molluscs and human brain. The B. lanceolatum neural tube contains relatively high amounts of L-Glu, L-Asp, L-Ala and L-Gly. Thus, the amphioxus neural tube has in common
with the molluscan and human nervous systems the presence of appreciable amounts of L-Glu and L-Asp, which suggests that they
are the most common neurotransmitters among these phylogenetically distant animal groups. The relatively high concentration
of L-Ala in amphioxus is consistent with that found in molluscs and the low concentration of taurine is consistent with that
described in the human brain.
The D-Asp concentration, very high in the molluscan nervous system, was rather low in amphioxus, although a little higher
than the extremely low amounts observed in the human brain. Our data on free amino acids composition is in agreement with
the intermediate phylogenetic position of cephalochordates, in terms of the evolutionary transition from simple to complex
neural systems. 相似文献
5.
Summary. Icilin, the peripheral cold channel agonist, activates TRPM8 and TRPA1, localized on dorsal root ganglia and trigeminal neurons
in rats. Icilin precipitates immediate wet-dog shakes in this species, which are antagonized by centrally acting mu and kappa
opioid agonists, implicating the central nervous system in the behavioral response. We studied the effect icilin has on glutamate
levels in the dorsal striatum, a brain region involved in movement. Icilin (0.25, 0.5 and 0.75 mg/kg, i.p.) elicited a dose-
and time-dependent increase in glutamate within the striatum, indicative of icilin’s neurochemical effect in rats. 相似文献
6.
Summary. Using microdialysis, the effects of endogenous glutamate on extracellular concentrations of taurine in striatum and nucleus
accumbens of the awake rat were investigated. The glutamate uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylic acid (PDC) was used to increase the extracellular concentration of glutamate. PDC (1, 2 and
4 mM) produced a dose-related increase of extracellular concentrations of glutamate and taurine in striatum and nucleus accumbens.
Increases of extracellular taurine were significantly correlated with increases of extracellular glutamate, but not with PDC
doses, which suggests that endogenous glutamate produced the observed increases of extracellular taurine in striatum and nucleus
accumbens. The role of ionotropic glutamate receptors on the increases of taurine was also studied. In striatum, perfusion
of the antagonists of NMDA and AMPA/kainate glutamate receptors attenuated the increases of extracellular taurine. AMPA/kainate,
but not NMDA receptors, also reduced the increases of extracellular taurine in nucleus accumbens. These results suggest that
glutamate-taurine interactions exist in striatum and nucleus accumbens of the awake rat.
Received March 5, 1999/Accepted September 22, 1999 相似文献
7.
Summary. The changes in the concentration and those of composition of alanine, aspartic acid and glutamic acid enantiomers were investigated
during manufacture of Cheddar cheese. The amount of D-alanine increased continuously during ripening following the liberation
of L-alanine originated from the proteolysis of milk proteins. There was slightly more D-aspartic and D-glutamic acid in the
dry matter of curd after pressing than before pressurization. The D-amino acid content and the ratio of the D-enantiomers
related to the total amount of free amino acids differed significantly among cheeses produced with different single-strain
starters. The D-amino acid composition changed during manufacture, but the influence of the strain selection was not significant
on the D-amino acid pattern. 相似文献
8.
Chronic intake of caffeine during gestation down regulates metabotropic glutamate receptors in maternal and fetal rat heart 总被引:1,自引:0,他引:1
Summary. Caffeine is the most widely consumed substance in the world which antagonizes adenosine effects. Adenosine acting through
A1 receptors inhibits glutamate release which binds to metabotropic glutamate receptors (mGluRs). Recently, we have shown that
maternal caffeine intake during gestation causes down-regulation of A1 and metabotropic glutamate receptors in the brain of both rat mothers and fetuses. In the present work we provide evidence
that caffeine also affects receptors in hearts, causing a decrease in mGluRs from both maternal and fetal hearts. A decrease
in Gq/11 and PLC β1 proteins level was also observed in both tissues. However, phospholipase C activity was only affected in fetal heart, being
significantly decreased. These results suggest an in vivo cross-talk mechanism between adenosine and glutamate receptors in peripheral tissues. Therefore, special attention should
be paid to caffeine ingestion during gestation. 相似文献
9.
Ossowska K Konieczny J Wardas J Pietraszek M Kuter K Wolfarth S Pilc A 《Amino acids》2007,32(2):179-188
Summary. Several data indicate that inhibition of glutamatergic transmission may be important to alleviate of parkinsonian symptoms.
Therefore, the aim of the present paper is to review recent studies on the search for putative antiparkinsonian-like effects
of mGluR ligands and their brain targets. In order to inhibit glutamatergic transmission, the group I mGluRs (mGluR1 and mGluR5)
were blocked, and group II (mGluR2/3) or III (mGluR4/7/8) mGluRs were activated.
Systemic or intrastriatal administration of group I mGluR antagonists (mGluR5 – MPEP, MTEP; mGluR1 – AIDA) was found to inhibit
parkinsonian-like symptoms (catalepsy, muscle rigidity) in rats. MPEP administered systemically and mGluR1 antagonists (AIDA,
CPCCOEt, LY367385) injected intrastriatally reversed also the haloperidol-increased proenkephalin (PENK) mRNA expression in
the striatopallidal pathway. Similarly, ACPT-1, a group III mGluR agonist, administered into the striatum, globus pallidus
or substantia nigra inhibited the catalepsy. Intrastriatal injection of this compound reduced the striatal PENK expression
induced by haloperidol. In contrast, a group II mGluR agonist (2R,4R-APDC) administered intrastriatally reduced neither PENK
expression nor the above-mentioned parkinsonian-like symptoms. Moreover, a mixed mGluR8 agonist/AMPA antagonist, (R,S)-3,4-DCPG,
administered systemically evoked catalepsy and enhanced both the catalepsy and PENK expression induced by haloperidol.
The results reviewed in this article seem to indicate that group I mGluR antagonists or some agonists of group III may possess
antiparkinsonian properties, and point at the striatopallidal pathway as a potential target of therapeutic intervention. 相似文献
10.
Summary. Polyamines, in particular spermine, as well as some natural and synthetic polyamine derivatives have been found to be blockers
of N-methyl-d-aspartate receptors. We developed novel, polyamine-based channel blockers to analyze the structure of NMDA receptors. Anthraquinone
polyamines block NMDA receptors with some selectivity compared to other glutamate receptors. Results using mutant NR1 and
NR2 subunits identified amino acid residues that influence blockade by anthraquinone polyamines. The head group (anthraquinone)
may be positioned at the selectivity filter/narrowest constriction of the channel and the polyamine tail penetrates this constriction
into the inner vestibule below the level of the selectivity filter. The results are consistent with other work showing that
NR1 (Asn616) and NR2B (Asn616), but not NR2B (Asn615), make the narrowest constriction of NMDA channel, and that the M3 segments
from the two subunits, which form the outer vestibule, are likely staggered relative to each other in the vertical axis of
the channel. 相似文献
11.
Summary. A series of 1-(N-ethoxycarbonylamino)alkylphosphonic monoesters were synthesized via three-component Mannich-type condensation of ethyl carbamate,
aldehydes and dichlorophosphites in benzene, followed by hydrolysis. 相似文献
12.
Summary. The influence of the operation conditions (temperature and residence time) of a thermic treatment on the total amount (free
and protein-bound) of amino acid enantiomers of dry fullfat soya was investigated. Total amino acid content was determined
using conventional ion-exchange amino acid analysis of total hydrolysates and chiral amino acid analysis was performed by
HPLC after precolumn derivatization with o-phthaldialdehyde and 1-thio-β-D-glucose tetraacetate. Contrary to corn that was investigated previously, notable racemization
was detected even at lower temperatures. At 140 °C the ratio of the D-enantiomer was 0.87% for glutamic acid, 2.81% for serine,
and 1.92% for phenylalanine; at 220 °C the ratios of the D-enantiomer of the above amino acids were 1.43, 4.61, and 4.68%,
respectively. The concentration of several L-amino acids decreased. At 220 °C there was 10% less L-glutamic acid, 17% less
L-serine, 5% less L-phenylalanine, 6.6% less L-aspartic, acid and 21% less L-lysine than in the control; their loss can be
assigned to different degrees of L – D conversion. While nearly complete transformation of L-phenylalanine can be attributed
to racemization, the main cause of the loss of L-lysine is not racemization. The treatments in the same order of magnitude
resulted in the formation of more D-amino acids and greater extent of racemization of amino acids in fullfat soya than that
of maize.
Authors’ address: J. Csapó, Faculty of Animal Science, Institute of Chemistry, University of Kaposvár, Guba S. u. 40., H-7400
Kaposvár, Hungary 相似文献
13.
Schizophrenics commonly demonstrate abnormalities in central filtering capability following repetitive sensory stimuli. Such sensory inhibition deficits can be mirrored in rodents following administration of psycho-stimulatory drugs. In the present study, male Sprague-Dawley rats were implanted with brain surface electrodes to record auditory evoked EEG potentials in a paired-stimulus paradigm, using 87 dB clicks delivered 0.5 s apart. Amphetamine (1.83 mg/kg, i.p.) produced the expected loss of sensory inhibition, as defined by an increase in the ratio between test (T) and conditioning (C) amplitudes at N40, a mid-latency peak of the evoked potentials. Also, the 5-HT(1A) agonist (R)-8-OH-DPAT caused a significant increase in the TC ratio at the highest dose studied (0.5 mg/kg s.c.), while the 5-HT(1A) antagonist (S)-UH-301 did not significantly affect the TC ratio at any dose studied (0.1-5 mg/kg s.c.). When administered with amphetamine, a lower dose of 8-OH-DPAT (0.1 mg/kg) and the highest dose of UH-301 tested (5 mg/kg, s.c.) were able to reverse the amphetamine-induced increase in TC ratio. The findings suggest that 5-HT(1A) signaling is involved in sensory inhibition and support the evaluation of 5-HT(1A) receptor active compounds in conditions with central filtering deficits, such as schizophrenia. 相似文献
14.
Summary. The concentrations of free amino acids in plasma change coordinately and their profiles show distinctive features in various
physiological conditions; however, their behavior can not always be explained by the conventional flow-based metabolic pathway
network. In this study, we have revealed the interrelatedness of the plasma amino acids and inferred their network structure
with threshold-test analysis and multilevel-digraph analysis methods using the plasma samples of rats which are fed diet deficient
in single essential amino acid.
In the inferred network, we could draw some interesting interrelations between plasma amino acids as follows: 1) Lysine is
located at the top control level and has effects on almost all of the other plasma amino acids. 2) Threonine plays a role
in a hub in the network, which has direct links to the most number of other amino acids. 3) Threonine and methionine are interrelated
to each other and form a loop structure. 相似文献
15.
Summary. Thermophilic proteins show substantially higher intrinsic thermal stability than their mesophilic counterparts. Amino acid
composition is believed to alter the intrinsic stability of proteins. Several investigations and mutagenesis experiment have
been carried out to understand the amino acid composition for the thermostability of proteins. This review presents some generalized
features of amino acid composition found in thermophilic proteins, including an increase in residue hydrophobicity, a decrease
in uncharged polar residues, an increase in charged residues, an increase in aromatic residues, certain amino acid coupling
patterns and amino acid preferences for thermophilic proteins. The differences of amino acids composition between thermophilic
and mesophilic proteins are related to some properties of amino acids. These features provide guidelines for engineering mesophilic
protein to thermophilic protein.
Authors’ addresses: Yuan-Jiang Pan, Institute of Chemical Biology and Pharmaceutical Chemistry, Zhejiang University, Zhejiang
University Road 38, Hangzhou 310027, China; Wei-Fen Li, Microbiology Division, College of Animal Science, Zhejiang University,
Hangzhou 310029, China 相似文献
16.
Two isoforms of chalcone synthase (CHS) were isolated from cDNA libraries derived from UV-A-irradiated anthocyanin-accumulating
(DCb) and non-accumulating (DCs) cell cultures of carrot (Daucus carota L.). The clones designated as DcCHS1, which were present only in the DCb library, had a deduced primary sequence of 389 amino
acids and an expected molecular mass of 42.7 kDa, and seem to be alleles of those cloned by Ozeki et al. (1993). The second
isoform (DcCHS2) was present in both libraries. It had the highest degree of similarity (97.7%) to parsley CHS over all 397
amino acids. The expected molecular mass of the corresponding protein was 43.6 kDa. Results obtained from Southern blot analysis
indicated the existence of at least two CHS genes in carrot. A transient enhancement of the DcCHS1 mRNA level after continuous
irradiation with UV-A light could only be observed in anthocyanin-accumulating cultures, whereas an increase in DcCHS2 mRNA
was seen in both cell lines. The maximum accumulation of CHS mRNA occurred 48 h after the onset of UV-A irradiation. In the
European wild carrot the accumulation of DcCHS1 mRNA was restricted to the red central flowers, whereas the DcCHS2 mRNA was
detectable in all red and white petals, as well as leaves, but was absent in stems and roots. The expression of DcCHS1 was
restricted to anthocyanin-accumulating cells or organs. The heterologous expression of both cDNAs in Escherichia coli resulted in immunostainable bands of different sizes on the Western blot and high levels of catalytic CHS activity.
Received: 2 September 1999 / Accepted: 30 November 1999 相似文献
17.
Summary. Amino acids analysis in single wheat embryonic protoplast was performed using capillary electrophoresis equipped with laser-induced
fluorescence (CE-LIF), combination with tissue culture technique. Reagent fluorescein isothiocyanate (FITC) was introduced
into living protoplasts by electroporation for intracellular derivatization. A special osmotic buffer (0.6 mol/L mannitol,
5 mmol/L CaCl2) was used to keep the osmotic balance of embryonic protoplasts during the protoplasts derivatization. After completion of
the derivatization reaction in the protoplasts, a single protoplast was drawn into the capillary tip by electroosmotic flow.
Then a 0.1 M NaOH lysing solution was injected by diffusion. The derivatized amino acids were separated by capillary electrophoresis
and detected by laser-induced fluorescence detection after the protoplast was lysed Nine amino acids were quantitatively and
qualitatively determined and compared in lysate and single protoplast of wheat embryonic cells respectively, with mean concentrations
of amino acids ranging from 2.68×10−5 mol/L to 18.18×10−5 mol/L in single protoplast. 相似文献
18.
Chromatographic determination of L- and D-amino acids in plants 总被引:1,自引:0,他引:1
Quantities of free L- and D-amino acids (L- and D-AAs) in plants (leaves of coniferous and decidious trees, fleshy fruits, leaf blades of fodder grasses, and seeds and seedlings of edible legumes) were determined. Amino acid (AA) enantiomers were converted into diastereomers using pre-column derivatization with o-phthaldialdehyde together with N-isobutyryl-L(or D)-cysteine followed by separation of the resulting fluorescent isoindol derivatives on an octadecylsilyl stationary phase using high-performance liquid chromatography. Relative amounts of D-AAs were also determined by enantioselective gas chromatography-mass spectrometry on Chirasil-L-Val. Free D-AAs acids in the range of about 0.2% up to 8% relative to the corresponding L-AAs acids were found in plants. D-Asp, D-Asn, D-Glu, D-Gln, D-Ser and D-Ala could be detected in most of the plants, and D-Pro, D-Val, D-Leu and D-Lys in certain plants. As D-AAs were detected in gymnosperms as well as mono- and dicotyledonous angiosperms of major plant families it is concluded that free D-AAs in the low percentage range are principle constituents of plants. 相似文献
19.
D. Rivera C. Inocencio C. Obón E. Carreño A. Reales F. Alcaraz 《Vegetation History and Archaeobotany》2002,11(4):295-314
The origins of capers, their use and cultivation are discussed. Capers seeds and charcoal are often recovered from archaeological
sites of the Mediterranean and West Asia. These are referred to as C. Spinosa L. This is mostly a group of cultivars restricted to localities surrounding the Western Mediterranean and some places in
the Eastern Mediterranean. Identification of the findings is discussed in terms of seed morphology, present distribution and
ancient uses of C. aegyptia Lam., C. sicula Veill., C. cartilaginea Decne, C. orientalis Veill., C. decidua (Forssk.) Edgew. and other species. Citations of Capparis in early Rabbinic, Mesopotamian and Greco-Roman texts are presented.
Received June 3, 2002 / Accepted October 8, 2002
Correspondence to: D. Rivera 相似文献
20.
Bittner S 《Amino acids》2006,30(3):205-224
Summary. Quinones and amino acids are usually compartmentally separated in living systems, however there are several junctions in which
they meet, react and influence. It occurs mainly in wounded, cut or crushed plant material during harvest, ensiling or disintegrating
cells. Diffusing polyphenols are oxidized by polyphenol oxidases (PPOs) to quinonic compounds, which associate reversibly
or irreversibly with amino acids and proteins. The reaction takes place with the free nucleophilic functional groups such
as sulfhydryl, amine, amide, indole and imidazole substituents. It results in imine formation, in 1,4-Michael addition via
nitrogen or sulphur and in Strecker degradation forming aldehydes. The formation and activity of quinone–amino acids conjugates
influences the colour, taste, and aroma of foods. Physical and physiological phenomena such as browning of foods, discoloration
of plants during processing, alteration of solubility and digestibility, formation of humic substances, germicidal activity,
cytotoxicity and more occur when quinones from disintegrating cells meet amino acids. The mechanisms of toxicity and the pathways
by which PCBs may be activated and act as a cancer initiator include oxidation to the corresponding quinones and reaction
with amino acids or peptides. Sclerotization of insect cuticle is a biochemical process involving also the reaction between
quinones and amino acid derivatives. 相似文献