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1.
Suenaga R Yamane H Tomonaga S Asechi M Adachi N Tsuneyoshi Y Kurauchi I Sato H Denbow DM Furuse M 《Amino acids》2008,35(1):107-113
Recently, we observed that central administration of L-arginine attenuated stress responses in neonatal chicks, but the contribution of nitric oxide (NO) to this response was minimal. The sedative and hypnotic effects of L-arginine may be due to L-arginine itself and/or its metabolites, excluding NO. To clarify the mechanism, the effect of intracerebroventricular (i.c.v.) injection of L-arginine metabolites on behavior under social separation stress was investigated. The i.c.v. injection of agmatine, a guanidino metabolite of L-arginine, had no effect during a 10 min behavioral test. In contrast, the i.c.v. injection of L-ornithine clearly attenuated the stress response in a dose-dependent manner, and induced sleep-like behavior. The L-ornithine concentration in the telencephalon and diencephalon increased following the i.c.v. injection of L-arginine. In addition, several free amino acids including L-alanine, glycine, L-proline and L-glutamic acid concentrations increased in the telencephalon. In conclusion, it appears that L-ornithine, produced by arginase from L-arginine in the brain, plays an important role in the sedative and hypnotic effects of L-arginine observed during a stress response. In addition, several other amino acids having a sedative effect might partly participate in the sedative and hypnotic effects of L-arginine. 相似文献
2.
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
3.
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
4.
Garcia RF Gazola VA Barrena HC Hartmann EM Berti J Toyama MH Boschero AC Carneiro EM Manso FC Bazotte RB 《Amino acids》2007,33(1):151-155
Summary. Our purpose was to determine the blood amino acid concentration during insulin induced hypoglycemia (IIH) and examine if the
administration of alanine or glutamine could help glycemia recovery in fasted rats. IIH was obtained by an intraperitoneal
injection of regular insulin (1.0 U/kg). The blood levels of the majority of amino acids, including alanine and glutamine
were decreased (P < 0.05) during IIH and this change correlates well with the duration than the intensity of hypoglycemia. On the other hand,
the oral and intraperitoneal administration of alanine (100 mg/kg) or glutamine (100 mg/kg) accelerates glucose recovery.
This effect was partly at least consequence of the increased capacity of the livers from IIH group to produce glucose from
alanine and glutamine. It was concluded that the blood amino acids availability during IIH, particularly alanine and glutamine,
play a pivotal role in recovery from hypoglycemia. 相似文献
5.
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
6.
Near infrared spectroscopy, cluster and multivariate analysis hyphenated to thin layer chromatography for the analysis of amino acids 总被引:1,自引:0,他引:1
Summary. A method based on near-infrared spectroscopy (NIRS) was developed for the rapid and non-destructive determination and quantification
of solid and dissolved amino acids. The statistical results obtained after optimisation of measurement conditions were evaluated
on the basis of statistical parameters, Q-value (quality of calibrations), R2, standard error of estimation (SEE), standard error of prediction (SEP), BIAS applying cluster and different multivariate
analytical procedures. Experimental optimisation comprised the selection of the highest suitable optical thin-layer (0.5,
1.0, 1.5, 2.0, 2.5, 3.0 mm), sample temperature (10–30 °C), measurement option (light fibre, 0.5 mm optical thin-layer; boiling
point tube; different types of cuvettes) and sample concentration in the range between 100 and 500 ppm. Applying the optimised
conditions and a 115-QS Suprasil? cuvette (V = 400 μl), the established qualitative model enabled to distinguish between different dissolved amino acids with
a Q-value of 0.9555. Solid amino acids were investigated in the transflectance mode, allowing to differentiate them with a
Q-value of 0.9155. For the qualitative and quantitative analysis of amino acids in complex matrices NIRS was established as
a detection system directly onto the plate after prior separation on cellulose based thin-layer chromatography (TLC) sheets
employing n-butanol, acetic acid and distilled water at a ratio of 8:4:2 (v/v/v) as an optimised mobile phase. Due to the
prior separation step, the established calibration curve was found to be more stable than the one calculated from the dissolved
amino acids. The found lower limit of detection was 0.01 mg/ml. Finally, this optimised TLC-NIRS method was successfully applied
for the qualitative and quantitative analysis of L-lysine in apple juice. NIRS is shown not only to offer a fast, non-destructive
detection tool but also to provide an easy-to-use alternative to more complicated detection methods such as mass spectrometry
(MS) for qualitative and quantitative TLC analysis of amino acids in crude samples. 相似文献
7.
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
8.
T Takeuchi E C Weinbach M Gottlieb L S Diamond 《Comparative biochemistry and physiology. B, Comparative biochemistry》1979,62(3):281-285
1. The enzymatic mechanism of oxygen uptake elicited by L-serine in axenically cultivated trophozoites of Entamoeba histolytica was investigated. 2. Of 22 amino acids examined, only L-serine stimulated oxygen consumption by intact and disrupted amoebae. 3. Pyruvate, a product of serine metabolism, also stimulated oxygen consumption in the amoebae. 4. Characterization of the oxygen uptake elicited by both L-serine and pyruvate, and analysis of the products of L-serine metabolism indicate that the amino acid is first converted to pyruvate. 5. L-Serine dehydratase, which catalyzes the deamination of serine to pyruvate, was detected primarily in the soluble fraction of the amoebae. D-Serine potently inhibited the enzyme, as well as oxygen uptake in the presence of L-serine but not in the presence of pyruvate. 6. The pyruvate formed is oxidized, at least in part, by a novel pyruvate oxidase involving the uptake of molecular oxygen. 相似文献
9.
γ-Glutamyl compounds and their enzymatic production using bacterial γ-glutamyltranspeptidase 总被引:1,自引:0,他引:1
Summary. Some amino acids and peptides, which have low solubility in water, become much more soluble following γ-glutamylation. Compounds
become more stable in the blood stream with γ-glutamylation. Several γ-glutamyl compounds are known to have favorable physiological
effects on mammals. γ-Glutamylation can improve taste and can stabilize glutamine in aqueous solution. Because of such favorable
features, γ-glutamyl compounds are very attractive. However, only a small number of γ-glutamyl amino acids have been studied
although many other γ-glutamyl compounds may have characteristics that will benefit humans. This is mainly because γ-glutamyl
compounds have not been readily available. An efficient and simple method of producing various γ-glutamyl compounds, especially
γ-glutamyl amino acids, using bacterial γ-glutamyltranspeptidase has been developed. With this method, modifications of reactive
groups of the substrate and energy source such as ATP are not required, and a wide-range of γ-glutamyl compounds can be synthesized.
Moreover, bacterial γ-glutamyltranspeptidase, a catalyst for this method, is readily available from the strain over-producing
this enzyme. The superiority of producing γ-glutamyl compounds with bacterial γ-glutamyltranspeptidase over other methods
of production is discussed. 相似文献
10.
Relationship of taurine and other amino acids in plasma and in neutrophils of septic trauma patients
Engel JM Mühling J Weiss S Kärcher B Löhr T Menges T Little S Hempelmann G 《Amino acids》2006,30(1):87-94
Summary. Recently, an interdependency of plasma taurine and other amino acids as well as metabolic and clinical variables implicating
therapeutic options was reported. This result may be an indication that plasma taurine levels are directly related to intracellular
levels. Therefore, the aim of this study was to analyse the possible relationship between taurine levels in plasma and in
neutrophils, the relationship to other amino acids, and variables quantifying metabolic impairment and severity of sepsis
in multiple trauma patients developing sepsis. After multiple trauma taurine decreased significantly in plasma in thirty-two
patients as well as within the neutrophil and does not recover in sepsis. Lower individual levels in the neutrophil did not
follow lower individual levels in plasma and no correlation of taurine in plasma and in the neutrophils could be observed.
In sepsis, only plasma showed an interdependency of taurine, aspartate, and glutamate. No association between taurine plasma
or intracellular levels and SOFA score as indicator for severity of sepsis or metabolic variables was observed. After multiple
trauma and in sepsis, taurine uptake in cells (which is regulated in different ways), and intracellular taurine (which serves
e.g. as an osmolyte) can be influenced. Therefore a prediction of the neutrophil taurine pool seems not fully possible from
taurine plasma levels. Intracellular taurine has some unique properties explaining the missing interdependency despite some
similarities in osmoregulation and metabolic interactions to other amino acids. The association of taurine, aspartate, and
glutamate in plasma cannot be simply transferred to the neutrophils intracellular level. The clinical meaning of the plasma
correlation remains unclear. A dependency of plasma and neutrophil taurine to severity of sepsis and to metabolic variables
seems not possible because of the multifactorial pathophysiology of sepsis. 相似文献
11.
Summary. Amino acids are widely used in biotechnology applications. Since amino acids are natural compounds, they can be safely used
in pharmaceutical applications, e.g., as a solvent additive for protein purification and as an excipient for protein formulations.
At high concentrations, certain amino acids are found to raise intra-cellular osmotic pressure and adjust to the high salt
concentrations of the surrounding medium. They are called “compatible solutes”, since they do not affect macromolecular function.
Not only are they needed to increase the osmotic pressure, they are known to increase the stability of the proteins. Sucrose,
glycerol and certain amino acids were used to enhance the stability of unstable proteins after isolation from natural environments.
The mechanism of the action of these protein-stabilizing amino acids is relatively well understood. On the contrary, arginine
was accidentally discovered as a useful reagent for assisting in the refolding of recombinant proteins. This effect of arginine
was ascribed to its ability to suppress aggregation of the proteins during refolding, thereby increasing refolding efficiency.
By the same mechanism, arginine now finds much wider applications than previously anticipated in the research and development
of proteins, in particular in pharmaceutical applications. For example, arginine solubilizes proteins from loose inclusion
bodies, resulting in efficient production of active proteins. Arginine suppresses protein–protein interactions in solution
and also non-specific adsorption to gel permeation chromatography columns. Arginine facilitates elution of bound proteins
from various column resins, including Protein-A or dye affinity columns and hydrophobic interaction columns. This review covers
various biotechnology applications of amino acids, in particular arginine. 相似文献
12.
Summary. The levels of proline and other amino acids in the haemolymph and other body parts of honeybee foragers were investigated
by HPLC analysis. The concentrations of proline in the blood of glucose-fed or -injected bees finishing their exhaustive tethered
flights on a roundabout were significantly reduced compared to bees that were fed and rested for one hour. This indicates
some utilization of proline during flight metabolism. The levels of essential amino acids and of the sum of all amino acids
except proline remained roughly constant, indicating that the decrease of proline did not result from a changed haemolymph
volume. 14C-labelled proline was injected into bees either shortly before starting their flight or before a resting period of equal
duration in an incubator at the same temperature. Bees that rested had incorporated more proline into thorax body protein,
and less of the labelled substance was unrecovered ("missing") and considered to be respired or less probably defecated. If
the entire amount of missing 14C-proline is regarded as exhaled, the oxidative breakdown of proline reached higher levels after flight than in rested bees.
This is another hint that proline is utilized during flight. Usually the exhaled amount did not exceed 10 μg proline in half an hour of flight. Although our data indicate involvement of proline in flight metabolism, the amount metabolized
is low compared to the utilization of carbohydrates.
Received December 5, 1998, Accepted February 1, 1999 相似文献
13.
Suenaga R Tomonaga S Yamane H Kurauchi I Tsuneyoshi Y Sato H Denbow DM Furuse M 《Amino acids》2008,35(1):139-146
L-arginine participates in many important and diverse biochemical reactions associated with the normal physiology of the organism. In the present study, we investigated the effect of central administration of L-arginine on the stress response and its mechanism in neonatal chicks. Intracerebroventricular (i.c.v.) injection of L-arginine clearly attenuated the stress response in a dose-dependent manner, and induced sleep-like behavior during 10 min. To clarify the mechanism by which L-arginine induces sedative and hypnotic effects in chicks, we investigated the effects of nitric oxide (NO) synthase (NOS) inhibitors on L-arginine-induced sedative and hypnotic effects, and as well as the effects of a NO donor. L-Arginine-induced (1.9 micromol) sedative and hypnotic effects were attenuated by i.c.v. co-injection with a non-selective NOS inhibitor N(G)-nitro-L-arginine methyl ester HCl (400 nmol). In addition, the effects of L-arginine were slightly attenuated by the inactive isomer of the NOS inhibitor N(G)-nitro-D-arginine methyl ester HCl (400 nmol). The i.c.v. injection of 3-morpholinosylnomine hydrochloride, a spontaneous NO donor, had little effect on postures. The i.c.v. injection of L-arginine had no effect on NOx concentration at various brain sites. These results suggested that the contribution of NO generation via NOS may be low in the sedative and hypnotic actions of L-arginine. Therefore, L-arginine and/or its metabolites, excluding NO, may be necessary for these actions. 相似文献
14.
Summary. Secondary amino acid disturbances from circulatory responses during hypoxia may cause problems in interpreting plasma amino
acid profiles of sick babies investigated for possible inherited defects. Systematic studies to characterise them are difficult
in man. We investigated the effects of hypoxia on plasma amino acids by studying 9 late gestation fetal sheep in utero during 11 one hour episodes of moderately severe isocapnic hypoxia. In 6 experiments, maternal plasma amino acids were also
monitored. Fourteen fetal plasma amino acids increased significantly, with the largest proportionate changes in alanine, valine,
leucine, isoleucine, phenylalanine, tyrosine, ornithine and lysine. Maternal amino acids did not increase. Probable explanations
were reflex peripheral vasoconstriction in skeletal muscle beds and decreased hepatic blood flow. The findings extend our
knowledge of the fetal response to hypoxic stress, demonstrate the importance of skeletal muscle in branched-chain amino acid
metabolism, and should help with interpretation of postnatal plasma amino acid disturbances.
Received January 29, 1999, Accepted February 22, 1999 相似文献
15.
Summary. Goldfish retinal explant outgrowth in the presence of fetal calf serum is stimulated by taurine. In the absence of it, but
with glucose in the medium, length of neurites is still elevated by the amino acid. Using the medium in the presence of glucose,
but in the absence of fetal calf serum, we explored the effect of optic tectum medium from cultures of them coming from goldfish
without crush of the optic nerve or 3, 5, 10, 14 and 20 days after crush. Retinal explants, intact or from goldfish with crush
of the optic nerve 10 days prior to starting the culture, were employed in order to measure the possible effect of optic tectum
media and the inter action with taurine. In other type of experiments the optic nerve was crushed 1, 2, 4, 7 and 10 days before
dissection of the optic tectum, and then co-cultured with intact or 10 days post-crush retinal explants. Optic tectum media
produced a time-dependent effect on outgrowth in lesioned retinas with a maximum effect around 5 days after the lesion for
the corresponding optic tectum. Taurine, 4 mM, did not further affect the outgrowth in the presence of optic tectum media,
but did significantly increase length of neurites either in intact or in post-lesion retinas. Co-culture of optic tectum at
different days post-lesion and retinas at 10 days post-lesion increased the outgrowth around 4 days post-lesion, in a preparation
resulting in mutual effects of both types of tissues. The addition of taurine in these conditions did not further increase
outgrowth, rather inhibited it according to the time after lesion of optic nerve corresponding to the co-cultured optic tectum.
The effect of taurine was concentration-dependent, since 0.2 mM was more effective than 2 or 4 mM in the presence of optic
tectum with lesion of 2 days. These results demonstrate the time-course of the regeneration processes in the visual system
of goldfish, indicating the crucial periods after crush in which the tectum could produce stimulation and later decrease or
no effect on outgrowth from the retina. In addition, they are evidences of the interaction between taurine and optic tectum
production of time-produced specific agents. The mechanisms underlying these effects are closely related to calcium, as it
was demonstrated by the addition of extracellular or intracellular chelators to the medium, which inhibited the effects of
the optic tectum and the trophic properties of taurine in this system. The inhibitor of taurine transport, guanidoethylsulfonate,
also decreased the stimulatory effects of the optic tectum and of taurine, indicating an interaction of substances produced
by the tectum with taurine, and an effect of taurine mediated through its entrance to the cells. Overall, retinal explants
outgrowth in the absence of fetal calf serum, the interaction of agents of the optic tectum and taurine modulates outgrowth
from the retina, and these effects are mediated by calcium levels and by the levels of intracellular taurine. 相似文献
16.
Summary. Aspartate is the common precursor of the essential amino acids lysine, threonine, methionine and isoleucine in higher plants.
In addition, aspartate may also be converted to asparagine, in a potentially competing reaction. The latest information on
the properties of the enzymes involved in the pathways and the genes that encode them is described. An understanding of the
overall regulatory control of the flux through the pathways is undisputedly of great interest, since the nutritive value of
all cereal and legume crops is reduced due to low concentrations of at least one of the aspartate-derived amino acids. We
have reviewed the recent literature and discussed in this paper possible methods by which the concentrations of the limiting
amino acids may be increased in the seeds. 相似文献
17.
K. Hamasu K. Shigemi Y. Tsuneyoshi H. Yamane H. Sato D. M. Denbow M. Furuse 《Amino acids》2010,38(1):57-64
The central effects of L-proline, D-proline and trans-4-hydroxy-L-proline were investigated by using the acute stressful model with neonatal chicks in Experiment 1. Sedative and hypnotic
effects were induced by all compounds, while plasma corticosterone release under isolation stress was only attenuated by L-proline.
To clarify the mechanism by which L-proline and D-proline induce sedative and hypnotic effects, the contribution of the strychnine-sensitive
glycine receptor (glycine receptor) and N-methyl-D-aspartate glutamate receptor (NMDA receptor) were further investigated. In Experiments 2–3, the glycine receptor
antagonist strychnine was co-injected intracerebroventricular (i.c.v.) with L-proline or D-proline. The suppression of isolation-induced
stress behavior by D-proline was attenuated by strychnine. However, the suppression of stress behavior by L-proline was not
attenuated. In Experiment 4, the NMDA receptor antagonist (+)-MK-801 was co-injected i.c.v. with L-proline. The suppression
of stress behavior by L-proline was attenuated by (+)-MK-801. These results indicate that L-proline and D-proline differentially
induce sedative and hypnotic effects through NMDA and glycine receptors, respectively. 相似文献
18.
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
19.
L-Serine alone is not gluconeogenic in isolated rabbit hepatocytes, whereas in rat liver this amino acid has been reported to yield as much glucose as does L-lactate itself. The current study has been an investigation into the explanation of the difference between the two species. Hepatocytes were isolated from 48-h-starved, 750- to 1000-g male rabbits, and the viability of each preparation was judged by ATP levels (2.4 +/- 0.2 mumol/g wet wt) at the beginning and end of the incubation as well as gluconeogenesis from 10 mM L-lactate (0.83 +/- 0.08 mumol/min/g wet wt). L-Serine alone produced virtually no glucose or pyruvate accumulation above baseline. Hydroxypyruvate, however, did appear in the incubation mixture. When L-serine and pyruvate were combined to test the functional activity of L-serine:pyruvate aminotransferase (EC 2.6.1.51), however, gluconeogenesis remained at the rate produced by pyruvate alone (0.61 +/- 0.04 mumol/min/g wet wt). On the other hand, the combination of L-serine and L-lactate produced rates of glucose accumulation 35% above that of L-lactate alone. The combination of L-lactate plus hydroxypyruvate produced nearly maximal rates (1.39 +/- 0.08 mumol/min/g wet wt), approaching those achieved by a physiologic ratio (10:1) of L-lactate and pyruvate. Hydroxypyruvate itself was only moderately gluconeogenic (0.44 +/- 0.04 mumol/min/g wet wt). That a reduction of the cytoplasmic free [NAD+]/[NADH] ratio by L-lactate was not its only contribution to L-serine utilization was suggested by the fact that ethanol completely eliminated gluconeogenesis from virtually all precursors (or combinations) tested, with the exception of hydroxypyruvate. It has been concluded from the data that, probably in contrast to the rat, the major pathway for the entrance of L-serine into gluconeogenesis in rabbit hepatocytes is through the pathway initiated by L-serine: pyruvate aminotransferase and that L-lactate is an important participant (i) by generating cytoplasmic reducing equivalents (NADH), (ii) by supplying pyruvate for the transaminating reaction itself, and, perhaps, (iii) by preventing hydroxypyruvate from being reduced by L-lactate dehydrogenase (EC 1.1.1.27) to L-glycerate. 相似文献
20.
Summary. The cDNA encoding D-aspartate oxidase (DASPO) was cloned from mouse kidney RNA by RT–PCR. Sequence analysis showed that it
contained a 1023-bp open reading frame encoding a protein of 341 amino acid residues. The protein was expressed in Escherichia coli with or without an N-terminal His-tag and had functional DASPO activity that was highly specific for D-aspartate and N-methyl-D-aspartate. To investigate the roles of the Arg-216 and Arg-237 residues of the mouse DASPO (mDASPO), we generated
clones with several single amino acid substitutions of these residues in an N-terminally His-tagged mDASPO. These substitutions
significantly reduced the activity of the recombinant enzyme against acidic D-amino acids and did not confer any additional
specificity to other amino acids. These results suggest that the Arg-216 and Arg-237 residues of mDASPO are catalytically
important for full enzyme activity. 相似文献