共查询到20条相似文献,搜索用时 0 毫秒
1.
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
2.
Leaf and minor vein structure were studied in Arabidopsis thaliana (L.) Heynh. to gain insight into the mechanism(s) of phloem loading. Vein density (length of veins per unit leaf area) is
extremely low. Almost all veins are intimately associated with the mesophyll and are probably involved in loading. In transverse
sections of veins there are, on average, two companion cells for each sieve element. Phloem parenchyma cells appear to be
specialized for delivery of photoassimilate from the bundle sheath to sieve element-companion cell complexes: they make numerous
contacts with the bundle sheath and with companion cells and they have transfer cell wall ingrowths where they are in contact
with sieve elements. Plasmodesmatal frequencies are high at interfaces involving phloem parenchyma cells. The plasmodesmata
between phloem parenchyma cells and companion cells are structurally distinct in that there are several branches on the phloem
parenchyma cell side of the wall and only one branch on the companion cell side. Most of the translocated sugar in A. thaliana is sucrose, but raffinose is also transported. Based on structural evidence, the most likely route of sucrose transport is
from bundle sheath to phloem parenchyma cells through plasmodesmata, followed by efflux into the apoplasm across wall ingrowths
and carrier-mediated uptake into the sieve element-companion cell complex.
Received: 5 October 1999 / Accepted: 20 November 1999 相似文献
3.
Summary. The purpose of the present study was to determine whether the regulation of brain protein synthesis was mediated through changes
in the plasma concentrations of insulin and growth hormone (GH), and whether the concentrations of amino acids in the brain
and plasma regulate the brain protein synthesis when the quantity and quality of dietary protein is manipulated. Two experiments
were done on three groups of aged rats given diets containing 20% casein, 5% casein or 0% casein (Experiment 1), and 20% casein,
20% gluten, or 20% gelatin (Experiment 2) for 1 d (only one 5-h period) after all rats were fed the 20% casein diet for 10
d (only 5-h feeding per day). The aggregation of brain ribosomes, the concentration in plasma GH, and the branched chain amino
acids in the plasma and cerebral cortex declined with a decrease of quantity and quality of dietary protein. The concentration
of plasma insulin did not differ among groups. The results suggest that the ingestion of a higher quantity and quality of
dietary protein increases the concentrations of GH and several amino acids in aged rats, and that the concentrations of GH
and amino acids are at least partly related to the mechanism by which the dietary protein affects brain protein synthesis
in aged rats. 相似文献
4.
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
5.
Chemical composition of apoplastic transport barriers in relation to radial hydraulic conductivity of corn roots (Zea mays L.) 总被引:5,自引:0,他引:5
The hydraulic conductivity of roots (Lpr) of 6- to 8-d-old maize seedlings has been related to the chemical composition of apoplastic transport barriers in the endodermis
and hypodermis (exodermis), and to the hydraulic conductivity of root cortical cells. Roots were cultivated in two different
ways. When grown in aeroponic culture, they developed an exodermis (Casparian band in the hypodermal layer), which was missing
in roots from hydroponics. The development of Casparian bands and suberin lamellae was observed by staining with berberin-aniline-blue
and Sudan-III. The compositions of suberin and lignin were analyzed quantitatively and qualitatively after depolymerization
(BF3/methanol-transesterification, thioacidolysis) using gas chromatography/mass spectrometry. Root Lpr was measured using the root pressure probe, and the hydraulic conductivity of cortical cells (Lp) using the cell pressure
probe. Roots from the two cultivation methods differed significantly in (i) the Lpr evaluated from hydrostatic relaxations (factor of 1.5), and (ii) the amounts of lignin and aliphatic suberin in the hypodermal
layer of the apical root zone. Aliphatic suberin is thought to be the major reason for the hydrophobic properties of apoplastic
barriers and for their relatively low permeability to water. No differences were found in the amounts of suberin in the hypodermal
layers of basal root zones and in the endodermal layer. In order to verify that changes in root Lpr were not caused by changes in hydraulic conductivity at the membrane level, cell Lp was measured as well. No differences
were found in the Lp values of cells from roots cultivated by the two different methods. It was concluded that changes in
the hydraulic conductivity of the apoplastic rather than of the cell-to-cell path were causing the observed changes in root
Lpr.
Received: 17 March 1999 / Accepted: 22 June 1999 相似文献
6.
Gravity independence of seed-to-seed cycling in Brassica rapa 总被引:2,自引:0,他引:2
Musgrave ME Kuang A Xiao Y Stout SC Bingham GE Briarty LG Levenskikh MA Sychev VN Podolski IG 《Planta》2000,210(3):400-406
Growth of higher plants in the microgravity environment of orbital platforms has been problematic. Plants typically developed
more slowly in space and often failed at the reproductive phase. Short-duration experiments on the Space Shuttle showed that
early stages in the reproductive process could occur normally in microgravity, so we sought a long-duration opportunity to
test gravity's role throughout the complete life cycle. During a 122-d opportunity on the Mir space station, full life cycles
were completed in microgravity with Brassica rapa L. in a series of three experiments in the Svet greenhouse. Plant material was preserved in space by chemical fixation, freezing,
and drying, and then compared to material preserved in the same way during a high-fidelity ground control. At sampling times
13 d after planting, plants on Mir were the same size and had the same number of flower buds as ground control plants. Following
hand-pollination of the flowers by the astronaut, siliques formed. In microgravity, siliques ripened basipetally and contained
smaller seeds with less than 20% of the cotyledon cells found in the seeds harvested from the ground control. Cytochemical
localization of storage reserves in the mature embryos showed that starch was retained in the spaceflight material, whereas
protein and lipid were the primary storage reserves in the ground control seeds. While these successful seed-to-seed cycles
show that gravity is not absolutely required for any step in the plant life cycle, seed quality in Brassica is compromised by development in microgravity.
Received: 3 August 1999 / Accepted: 27 August 1999 相似文献
7.
8.
The effects of thiopentone on free intracellular amino acids in polymorphonuclear leucocytes 总被引:1,自引:0,他引:1
Summary. Previous studies have shown the inhibitory effects of thiopentone on polymorphonuclear leucocyte (PML) function. However,
major biochemical mechanisms which have been involved are still unknown. The aim of this study was therefore to investigate
thiopentone's effects on intracellular amino acid metabolism in PML using both advanced PML separation – and HPLC techniques,
especially developed for this purpose and precisely validated in our institute. Overall, our study indicates important dose-dependent
alterations of free intracellular amino acid metabolism following thiopentone treatment and draw attention to the biochemical
mechanisms which may be involved in both thiopentone-induced modulation in PML function and cellular immunocompetence.
Received April 4, 1999 相似文献
9.
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
10.
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
11.
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
12.
During sunflower (Helianthus annuus L.) seed formation there was an active period of lipid biosynthesis between 12 and 28 days after flowering (DAF). The maximum
in-vitro acyl-acyl carrier protein (ACP) thioesterase activities (EC 3.1.2.14) were found at 15 DAF, preceding the largest
accumulation of lipid in the seed. Data from the apparent kinetic parameters, V
max and K
m, from seeds of 15 and 30 DAF, showed that changes in acyl-ACP thioesterase activity are not only quantitative, but also qualitative,
since, although the preferred substrate was always oleoyl-ACP, the affinity for palmitoyl-ACP decreased, whereas that for
stearoyl-ACP increased with seed maturation. Bisubstrate assays carried out at 30 DAF seemed to indicate that the total activity
found in mature seeds is due to a single enzyme with 100/75/15 affinity for oleoyl-ACP/stearoyl-ACP/palmitoyl-ACP. In contrast,
at 15 DAF, enzymatic data together with partial sequences from cDNAs indicated the presence of at least two enzymes with different
properties, a FatA-like thioesterase, with a high affinity for oleoyl-ACP, plus a FatB-like enzyme, with preference for long-chain
saturated fatty acids, both being expressed during the active lipid biosynthesis period. Competition assays carried out with
CAS-5, a mutant with a higher content of palmitic acid in the seed oil, indicated that a modified FatA-type thioesterase is
involved in the mutant phenotype.
Received: 17 December 1999 / Accepted: 25 February 2000 相似文献
13.
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
14.
Two systems mediating the transport of amino acids were studied in vesicles derived from protein-depleted membranes of pigeon erythrocytes. One system (ASC system) catalysed the Na+-dependent exchange of small neutral amino acids, such as alanine, serine and cysteine. The other system, also Na+-dependent, mediated the active transport of glycine. The ASC and glycine systems were distinguished by the sensitivity of the latter to the anion present, by the former's requirement for an exchangeable amino acid and by the inability of alanine to inhibit the transport of glycine. Preliminary results indicated that the influx of glycine was electrically silent. The only major integral protein retained in the vesicles was the band 3 protein, but that could not be unequivocally identified as the transporter. 相似文献
15.
Selection for high seed oil content in soybean families derived from plants regenerated from protoplasts and tissue cultures 总被引:2,自引:0,他引:2
M. V. Nguyen C. D. Nickell J. M. Widholm 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2001,102(6-7):1072-1075
Recurrent selection for high seed oil content was carried out with 2,008 progeny of 28 plants regenerated via embryogenesis,
95 via organogenesis and 25 from protoplasts via organogenesis from five different soybean cultivars. Two lines derived from
plants regenerated from the cultivar Jack with small increases in seed oil content emerged after three selection cycles in
the field but in both cases the protein content was decreased and the seed yield of one of the lines was also decreased. Apparently
somaclonal variation for seed oil content can arise, but on the basis of the decreases in protein and yield found in this
study, this small change is not useful for soybean improvement.
Received: 22 July 2000 / Accepted: 28 July 2000 相似文献
16.
The effect of altered ergosterol content on the transport of various amino acids in Candida albicans
Candida albicans cells have low levels of ergosterol when grown in ascorbic acid-supplemented media. When cells are grown in hydroquinone-supplemented media, the ergosterol levels became higher as compared to normal cells. The uptake of lysine, glycine, glutamic acid, proline, methionine and serine is reduced in hydroquinone-supplemented cells. In contrast to hydroquinone-supplemented cells, the rate and level of accumulation of these amino acids are higher in ascorbic acid-supplemented cells. Nystatin-resistant isolates of C. albicans with low ergosterol contents also exhibit an increased rate and level of accumulation of these amino acids. The uptake of phenylalanine and leucine remained unaffected by such a change in ergosterol levels brought about by different supplementation of the media. The results demonstrate a correlation between ergosterol levels and amino acids uptake. Contrary to various reports, the rate of K+ efflux does not seem to correlate with the amino acid uptake in C. albicans cells. 相似文献
17.
The two genes homologous to Arabidopsis FAE1 co-segregate with the two loci governing erucic acid content in Brassica napus 总被引:1,自引:0,他引:1
M. Fourmann P. Barret M. Renard G. Pelletier R. Delourme D. Brunel 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1998,96(6-7):852-858
KCS (β-keto-acyl-CoA synthase) has been proposed as a candidate gene for explaining the erucic acid level in rapeseed. Degenerate
PCR primers corresponding to the FAE1 gene have been designed. Two B. napus genes BN-FAE1.1 and BN-FAE1.2, corresponding to the parental species B. rapa and B. oleracea FAE1 genes, were amplified. Polymorphism was revealed for these two genes by acrylamide electrophoresis of the amplification products.
These two genes could then be mapped and a co-segregation of these genes with the E1 and E2 loci controlling erucic acid content was found. Furthermore, mutations observed for one of these genes could explain part
of the low erucic trait of the three LEAR types used in this study.
Received: 3 November 1997 / Accepted: 25 November 1997 相似文献
18.
Summary. Amino acids (AA) are components of protein and precursors of many important biological molecules. To address effects of the
genes associated with metabolism and transport of AA and their derivatives during rat liver regeneration (LR), we firstly
obtained the above genes by collecting databases data and retrieving related thesis, and then analyzed their expression profiles
during LR using Rat Genome 230 2.0 array. The LR-associated genes were identified by comparing the gene expression difference
between partial hepatectomy (PH) and sham-operation (SO) rat livers. It was approved that 134 genes associated with metabolism
of AA and their derivatives and 26 genes involved in transport of them were LR-associated. The initially and totally expressing
number of these genes occurring in initial phase of LR (0.5–4 h after PH), G0/G1 (4–6 h after PH), cell proliferation (6–66 h
after PH), cell differentiation and structure-function reconstruction of liver tissue (72–168 h after PH) were respectively
76, 17, 79, 5 and 162, 89, 564, 195, illustrating that these LR-associated genes were initially expressed mainly in initial
stage, and functioned in different phases. Frequencies of up-regulation and down-regulation of them being separately 564 and
357 demonstrated that genes up-regulated outnumbered those down-regulated. Categorization of their expression patterns into
22 types implied the diversity of cell physiological and biochemical activities. According to expression changes and patterns
of the above-mentioned genes in LR, it was presumed that histidine biosynthesis in the metaphase and anaphase, valine metabolism
in the anaphase, and metabolism of glutamate, glutamine, asparate, asparagine, methionine, alanine, leucine and aromatic amino
acid almost were enhanced in the whole LR; as for amino acid derivatives, transport of neutral amino acids, urea, γ-aminobutyric
acid, betaine and taurine, metabolism of dopamine, heme, S-adenosylmethionine, thyroxine, and biosynthesis of hydroxyproline,
nitric oxide, orinithine, polyamine, carnitine, selenocysteine were augmented during the entire liver restoration. Above results
showed that metabolism and transport of AA and their derivates were necessary in liver regeneration.
Authors’ address: Prof. Dr. C. S. Xu, College of Life Science, No. 46, Jianshe RD, Henan, Xinxiang 453007, China 相似文献
19.
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
20.
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