共查询到20条相似文献,搜索用时 46 毫秒
1.
Brandsch M 《Amino acids》2006,31(2):119-136
Summary. Membrane transport of L-proline has received considerable attention in basic and pharmaceutical research recently. Of the
most recently cloned members of the solute carrier family, two are “proline transporters”. The amino acid transporter PAT1,
expressed in intestine, kidney, brain and other organs, mediates the uptake of proline and derivatives in a pH gradient-dependent
manner. The Na+-dependent proline transporter SIT1, cloned in 2005, exhibits the properties of the long-sought classical IMINO system. Proline-containing
peptides are of interest for several reasons. Many biologically important peptide sequences contain highly conserved proline
residues. Xaa-Pro peptides are very often resistant to enzymatic hydrolysis and display, in contrast to Pro-Xaa peptides,
a high affinity to the H+/peptide cotransporter PEPT1 which is expressed in intestinal, renal, lung and biliary duct epithelial cells. Furthermore,
several orally available drugs are recognized by PEPT1 as Xaa-Pro analogues due to their sterical resemblance to small peptides. 相似文献
2.
Summary. 6-N-carboxymethyllysine (CML), generated by the glycation and/or oxidation of lysine residues, has been measured in biological
materials and food products using techniques such as ELISA, HPLC with fluorescence detection and mass spectrometry methods.
Only limited information has been reported regarding the preparation of standards labeled with either deuterium, 13C or 15N atoms to be used as internal standards. In the present paper, a synthesis of carbon-13 labeled CML is described using l,2-13C2-glyoxylic acid and 2-N-acetyllysine as starting materials. The resulting labeled 2-N-acetyl-CML was purified by HPLC-UV as a dibutyl ester. After a deprotection step, the yield was evaluated to be 53% when
the reaction was conducted 17 h at 37°C. CML was extensively studied by 1H- and 13C-NMR and the fragments observed in the collision induced dissociation (CID) spectrum were also assigned. Finally, the standards
of CML and carbon-13 labeled CML were accurately quantified based on 1H-NMR and tandem MS using lysine as an internal reference. 相似文献
3.
Mühling J Nickolaus KA Halabi M Fuchs M Krüll M Engel J Wolff M Matejec R Langefeld TW Welters ID Menges T Dehne MG Sablotzki A Hempelmann G 《Amino acids》2005,29(3):289-300
Summary. The objective of this study was to determine the dose as well as duration of exposure-dependent effects of L-alanyl-L-glutamine,
arginine or taurine on polymorphonuclear neutrophil (PMN) free α-keto acid profiles and, in a parallel study, on PMN immune
functions. Exogenous L-alanyl-L-glutamine significantly increased PMN α-ketoglutarate, pyruvate PMN superoxide anion (O2−) generation, hydrogen peroxide (H2O2) formation and released myeloperoxidase (MPO) activity. Arginine also led to significant increases in α-ketoglutarate, pyruvate,
MPO release and H2O2 generation. Formation of O2− on the other hand was decreased by arginine. Incubation with taurine resulted in lower intracellular pyruvate and α-ketobutyrate
levels, decreased O2− and H2O2 formation and a concomitant significantly increased MPO activity. We therefore believe that considerable changes in PMN free-α-keto-acid
profiles, induced for example by L-alanyl-L-glutamine, arginine or taurine, may be one of the determinants in cell nutrition
that considerably modulates the immunological competence of PMN. 相似文献
4.
Summary. The present study was designed to evaluate the relevance of arginine transport in nitric oxide (NO) synthesis in vascular
smooth muscle cells. For this purpose, NO synthesis and arginine transport (system B0,+ and y+) were evaluated in cells treated with IL-1β or angiotensin II (Ang II). In addition, the effects of 5 mM lysine and glutamine, competitive inhibitors of systems y+ and B0,+ respectively, were examined. L-arginine transport was estimated with 3H-labelled arginine and NO was determined with the Griess reagent. These studies were done in control conditions, arginine-starved
cells, and in cells incubated in media containing 10 mM arginine. Our data indicate that induction of NO biosynthesis by IL-1β
depends on external arginine when cells are arginine-depleted for 24 hours. The concentration of arginine producing half maximal
activation of NO synthesis in arginine-depleted cells ([arginine]i < 10 μM) was 41.1 ± 18 μM. By contrast, in normal culture conditions, NO synthesis occurred independently of arginine transport.
Neither 5 mM lysine or glutamine which abolished arginine transport through systems y+ and B0,+, respectively, reduced nitrite release in cells incubated in normal media. This suggests that the relevance of arginine uptake
to NO synthesis depends on the status of intracellular arginine pools. Intracellular arginine concentrations were not affected
by the stimulation of NO production using IL-1β or its inhibition using Ang II, but were markedly reduced by arginine starvation
for 48 h. Aspartate levels were also reduced by arginine-depletion, but were not affected in cells incubated with 10 mM arginine.
By contrast, glutamate levels were reduced in arginine-starved cells and were increased in cells incubated in arginine-supplemented
medium. Ornithine levels were markedly increased by arginine supplementation. Altogether, these findings indicate that NO
synthesis is normally independent of membrane transport. However in arginine-depleted cells, membrane transport is essential
for NO synthesis. It is concluded that arginine transport is required for the long-term maintenance of intracellular arginine
pools.
Received February 7, 1999; Accepted June 21, 1999 相似文献
5.
Summary. The paper describes the synthesis of α-aminosuberic acid derivatives suitable for the synthesis of peptides. These include Z-, Boc- and Fmoc-protection on the α-amino group, benzyl ester, Boc-hydrazide and Z-hydrazide as well as the free carboxylic function in the side chain, and methyl
ester, benzyl ester or free α-carboxylic group. Their use is demonstrated on the synthesis of the respective derivatives of Asu-Val-Leu. The enzyme catalyzed
reaction was succesfully used both as a route to L-Asu from the D,L-compound as well as for the direct synthesis of the optically
active tripeptide derivative from the Z-D,L-Asu-OH.
Received February 5, 1999 相似文献
6.
Jose Neptuno Rodriguez-Lopez Andrew T. Smith R. N. F. Thorneley 《Journal of biological inorganic chemistry》1996,1(2):136-142
Horseradish peroxidase isoenzyme C (HRPC) mutants were constructed in order to understand the role of two key distal haem
cavity residues, histidine 42 and arginine 38, in the formation of compound I and in substrate binding. The role of these
residues as general acid-base catalysts, originally proposed for cytochrome c peroxidase by Poulos and Kraut in 1980 was assessed for HRPC. Replacement of histidine 42 by leucine [(H42L)HRPC*] decreased
the apparent bimolecular rate constant for the reaction with hydrogen peroxide by five orders of magnitude (k
1 = 1.4×102 M–1s–1) compared with both native-glycosylated and recombinant forms of HRPC (k
1 = 1.7×107 M–1s–1). The first-order rate constant for the heterolytic cleavage of the oxygen-oxygen bond to form compound I was estimated to
be four orders of magnitude slower for this variant. Replacement of arginine 38 by leucine [(R38L)HRPC*] decreased the observed
pseudo-first-order rate constant for the reaction with hydrogen peroxide by three orders of magnitude (k
1 = 1.1×104 M–1s–1), while the observed rate constant of oxygen bond scission was decreased sixfold (k
2 = 142 s–1). These rate constants are consistent with arginine 38 having two roles in catalysing compound I formation: firstly, promotion
of proton transfer to the imidazole group of histidine 42 to facilitate peroxide anion binding to the haem, and secondly,
stabilisation of the transition state for the heterolytic cleavage of the oxygen-oxygen bond. These roles for arginine 38
explain, in part, why dioxygen-binding globins, which do not have an arginine in the distal cavity, are poor peroxidases.
Binding studies of benzhydroxamic acid to (H42L)HRPC* and (R38L)HRPC* indicate that both histidine 42 and arginine 38 are
involved in the modulation of substrate affinity.
Received: 21 July 1995 / Accepted: 27 November 1995 相似文献
7.
In this paper, the reactions of bovine insulin and small peptides, such as actin binding domain of thymosin β4 and Growth Hormone Releasing Factor (GRF 1–29 amino acids) with diisopropyloxyphosphite (DIPPH) and dimethyloxyphosphite (DMPH) were studied by modified Todd reaction. The MALDI-TOF or ESI-MS results showed that lysine, histidine and arginine residues in insulin could be phosphorylated under the water/ethanol system. The N,N,N-diisopropyloxyphosphorylated insulin analogues were characterized using MALDI-TOF and 31P NMR. These insulin analogues with different phosphorylation degree were separated and identified through LC-ESI-MS. In addition, circular dichroism (CD) spectra showed that the conformation of N,N,N-dimethyloxyphosphorylated insulin were only changed a little, whereas, that of N,N,N-diisopropyloxyphosphorylated insulin was changed completely. 相似文献
8.
Mesnard F Azaroual N Marty D Fliniaux MA Robins RJ Vermeersch G Monti JP 《Planta》2000,210(3):446-453
Nitrogen metabolism was monitored in suspension cultured cells of Nicotiana plumbaginifolia Viv. using nuclear magnetic resonance (NMR) spectroscopy following the feeding of (15NH4)2SO4 and K15NO3. By using two-dimensional 15N-1H NMR with heteronuclear single-quantum-coherence spectroscopy and heteronuclear multiple-bond-coherence spectroscopy sequences,
an enhanced resolution of the incorporation of 15N label into a range of compounds could be detected. Thus, in addition to the amino acids normally observed in one-dimensional
15N NMR (glutamine, aspartate, alanine), several other amino acids could be resolved, notably serine, glycine and proline. Furthermore,
it was found that the peak normally assigned to the non-protein amino-acid γ-aminobutyric acid in the one-dimensional 15N NMR spectrum was resolved into a several components. A peak of N-acetylated compounds was resolved, probably composed of the intermediates in arginine biosynthesis, N-acetylglutamate and N-acetylornithine and, possibly, the intermediate of putrescine degradation into γ-aminobutyric acid, N-acetylputrescine. The occurrence of 15N-label in agmatine and the low detection of labelled putrescine indicate that crucial intermediates of the pathway from glutamate
to polyamines and/or the tobacco alkaloids could be monitored. For the first time, labelling of the peptide glutathione and
of the nucleotide uridine could be seen.
Received: 29 March 1999 / Accepted: 15 July 1999 相似文献
9.
Summary. Our aim was to determine changes in free amino acid (FAA) and dipeptide (DP) concentrations in probable Alzheimer’s disease
(pAD) subjects compared with control (CT) subjects using liquid chromatography and electrospray ionization tandem mass spectrometry
(LCMS2). We recruited gender- and age-matched study participants based on neurological and neuropsychological assessments. We measured
FAAs and DPs in cerebrospinal fluid (CSF), plasma and urine using LCMS2 with selected reaction monitoring (SRM). Imidazole-containing FAAs (histidine, methyl-histidine), catecholamines (L-DOPA
and dopamine), citrulline, ornithine, glycine and antioxidant DPs (carnosine and anserine) accounted for the major changes
between CT and pAD. Carnosine levels were significantly lower in pAD (328.4 ± 91.31 nmol/dl) than in CT plasma (654.23 ± 100.61 nmol/dl).
In contrast, L-DOPA levels were higher in pAD (1400.84 ± 253.68) than CT (513.10 ± 121.61 nmol/dl) plasma. These data underscore
the importance of FAA and DP metabolism in the pathogenesis of AD. Since our data show changes in antioxidants, neurotransmitters
and their precursors, or FAA associated with urea metabolism in pAD compared with CT, we propose that manipulation of these
metabolic pathways may be important in preventing AD progression. 相似文献
10.
H. Kubo Y. Ikeda-Moore A. Kikuchi Kiyoshi Miwa Kiyoshi Nokihara Christian Schönbach M. Takiguchi 《Immunogenetics》1998,47(3):256-263
HLA-B*3501 and -B*5101 molecules, which belong to the HLA-B5 cross-reactive group, bind peptides carrying similar anchor residues at P2 and
the C-terminus, but differences are observed in the preference for a Tyr residue at the C-terminus and the affinity of peptides.
A recent study of HLA-B*3501 crystal structure suggested that residue 116 on the floor of the F-pocket determines a preference for anchor residues
at the C-terminus. In order to evaluate the role of the residue 116 in the peptide binding to both HLA-B*3501 and HLA-B*5101 molecules, we generated HLA-B*3501 mutant molecules carrying Tyr at residue 116 (B*3501–116Y) and tested the binding of a panel of nonamer peptides to the B*3501–116Y molecules by a stabilization assay with RMA-S transfectants expressing the mutant molecules. The substitution of
Tyr for Ser at residue 116 markedly reduced the affinity of nonamer peptides carrying Tyr at P9, while it enhanced that of
nonamer peptides carrying Ile and Leu at P9. On the other hand, the affinity of peptides carrying aliphatic hydrophobic residues
at P9 to B*3501–116Y molecules was much higher than that to HLA-B*3501 and HLA-B*5101 molecules. These results indicate that residue 116 is critical for the structural difference of the F-pocket between
HLA-B*3501 and HLA-B*5101 which determines the C-terminal anchor residues, while leaving other residues which differ between HLA-B*3501 and HLA-B*5101 may be responsible for the low peptide binding property of the latter.
Received: 18 April 1997 / Revised: 18 September 1997 相似文献
11.
Summary. In continuation of our previous work dedicated to the detection of the oxidation products of aminoethylcysteine ketimine
dimer by oxygen reactive species, we give here data for the identification of the α, β unsaturated sulfoxide as the main product of interaction of the dimer with H2O2. Identification has been done on the basis of mass spectrometry and NMR analyses of the product isolated by preparative chromatography.
Received March 24, 1998, Accepted October 20, 1998 相似文献
12.
Guangshun Wang 《生物化学与生物物理学报:生物膜》2010,1798(2):114-12455
Worldwide bacterial resistance to traditional antibiotics has drawn much research attention to naturally occurring antimicrobial peptides (AMPs) owing to their potential as alternative antimicrobials. Structural studies of AMPs are essential for an in-depth understanding of their activity, mechanism of action, and in guiding peptide design. Two-dimensional solution proton NMR spectroscopy has been the major tool. In this article, we describe the applications of natural abundance 13C NMR spectroscopy that provides complementary information to 2D 1H NMR. The correlation of 13Cα secondary shifts with both 3D structure and heteronuclear 15N NOE values indicates that natural abundance carbon chemical shifts are useful probes for backbone structure and dynamics of membrane peptides. Using human LL-37-derived peptides (GF-17, KR-12, and RI-10), as well as amphibian antimicrobial and anticancer peptide aurein 1.2 and its analog LLAA, as models, we show that the cross peak intensity plots of 2D 1H-13Cα HSQC spectra versus residue number present a wave-like pattern (HSQC wave) where key hydrophobic residues of micelle-bound peptides are located in the troughs with weaker intensities, probably due to fast exchange between the free and bound forms. In all the cases, the identification of aromatic phenylalanines as a key membrane-binding residue is consistent with previous intermolecular Phe-lipid NOE observations. Furthermore, mutation of one of the key hydrophobic residues of KR-12 to Ala significantly reduced the antibacterial activity of the peptide mutants. These results illustrate that natural abundance heteronuclear-correlated NMR spectroscopy can be utilized to probe backbone structure and dynamics, and perhaps to map key membrane-binding residues of peptides in complex with micelles. 1H-13Cα HSQC wave, along with other NMR waves such as dipolar wave and chemical shift wave, offers novel insights into peptide-membrane interactions from different angles. 相似文献
13.
Z. He N. Petesch K.-P. Voges W. Röben K.D. Philipson 《The Journal of membrane biology》1997,156(2):149-156
The Na+-Ca2+ exchanger plays an important role in cardiac contractility by moving Ca2+ across the plasma membrane during excitation-contraction coupling. A 20 amino acid peptide, XIP, synthesized to mimic a region
of the exchanger, inhibits exchange activity. We identify here amino acid residues important for inhibitory function. Effects
of modified peptides on Na+-Ca2+ exchange activity were determined. Exchange activity was assessed as 45Ca2+ uptake into Na+-loaded cardiac sarcolemmal vesicles. We find that the entire length of XIP is important for maximal potency, though the major
inhibitory components are between residues 5 and 16. Basic and aromatic residues are most important for the inhibitory function
of XIP. Substitutions of arginine 12 and arginine 14 with alanine or glutamine dramatically decrease the potency of XIP, suggesting
that these residues play a key role in possible charge-charge interactions. Substitutions of other basic residues with alanines
or glutamines had less effect on the potency of XIP. All aromatic residues participate in binding with the exchanger, probably
via hydrophobic interactions as indicated by tryptophan fluorescence. A tyrosine is required at position 6 for maximal inhibition
and phenylalanine 5 and tyrosine 8 can only be replaced by other aromatic residues. Tyrosine 10 and tyrosine 13 can be replaced
with other bulky residues. A specific conformation of XIP, with structural constrains provided by all parts of the molecule,
is required for optimal inhibitory function.
Received: 19 September 1996/Revised: 20 November 1996 相似文献
14.
Døskeland AP 《Amino acids》2006,30(1):99-103
Summary. A simple method is described to identify signature peptides derived from polyubiquitin (polyUb) chains. The method is based
on MALDI-TOF MS/MS analysis after chemically assisted fragmentation, and works on peptides isolated from polyacrylamide gels.
PolyUb chains branched at K48 and K63 were chosen as models for Ub-protein conjugates. They were resolved by SDS-PAGE, and
their tryptic peptides (in-gel-trypsinolysis) derivatized with 3-sulfopropinic acid NHSester to obtain chemically assisted
fragmentation during the MS/MS analysis. PolyUb-K63 produced a single peptide identified as 55TLSDYNIQK63 (GG)ESTLHLVLR72. PolyUb-K48 produced two branched signature peptides identified as 43LIFAGK48(GG)QLEDGR54 and 43LIFAGK48(LRGG)QLEDGR54. The recovery of signature peptide with LRGG as branched chain underscores the need to take limited proteolysis into account
in the search for detection of ubiquitinated peptides in proteomics studies. In conclusion, a simple method has been described
allowing the identification of signature peptides, which are diagnostic markers of the majority of polyUb-conjugated proteins.
In principle, the method should be applicable also for other more rare signature peptides. 相似文献
15.
Geranylhydroquinone 3′′-hydroxylase, a cytochrome P-450 monooxygenase from Lithospermum erythrorhizon cell suspension cultures 总被引:2,自引:0,他引:2
Geranylhydroquinone 3′′-hydroxylase, which is likely to be involved in shikonin and dihydroechinofuran biosynthesis, was
identified in cell suspension cultures of Lithospermum erythrorhizon Sieb. et Zucc. (Boraginaceae). The enzyme hydroxylates the isoprenoid side chain of geranylhydroquinone (GHQ), a known precursor
of shikonin. Proton/proton correlation spectroscopic and proton/proton long-range correlation spectroscopic studies confirmed
that hydroxylation takes place specifically at position 3′′, i.e. at the methyl group involved in the cyclization reaction.
The enzyme is membrane-bound and was found in the microsomal fraction. It requires NADPH and molecular oxygen as cofactors,
and is inhibited by cytochrome P-450 inhibitors such as cytochrome c and CO. The inhibitory effect of CO is reversed by illumination.
These data suggest that the enzyme is a cytochrome P-450-dependent monooxygenase. The optimum pH of GHQ 3′′-hydroxylase is
7.4, and the apparent K
m value for GHQ is 1.5 μM. The reaction velocity obtained with 3-geranyl-4-hydroxybenzoic acid was more than 100 times lower
than that obtained with geranylhydroquinone.
Received: 20 March 1999 / Accepted: 20 July 1999 相似文献
16.
Maize (Zea mays L.) cell cultures incorporated radioactivity from [14C]cinnamate into hydroxycinnamoyl-CoA derivatives and then into polysaccharide-bound feruloyl residues. Within 5–20 min, the
CoA pool had lost its 14C by turnover and little or no further incorporation into polysaccharides then occurred. The system was thus effectively a
pulse–chase experiment. Kinetics of radiolabelling of diferulates (also known as dehydrodiferulates) varied with culture age.
In young (1–3 d) cultures, polysaccharide-bound [14C]feruloyl- and [14C]diferuloyl residues were both detectable within 1 min of [14C]cinnamate feeding. Thus, feruloyl residues were dimerised <1 min after their attachment to polysaccharides. For at least
the first 2.3 h after [14C]cinnamate feeding, polysaccharide-bound [14C]diferuloyl residues remained almost constant at ≈7% of the total polysaccharide-bound [14C]ferulate derivatives. Since feruloyl residues are attached to polysaccharides <1 min after the biosynthesis of the latter,
and >10 min before secretion, the data show that extensive feruloyl coupling occurred intra-protoplasmically. Exogenous H2O2 (1 mM) caused little additional feruloyl coupling; therefore, wall-localised coupling may have been peroxidase-limited. In
older (e.g. 4 d) cultures, less intraprotoplasmic coupling occurred: during the first 2.5 h, polysaccharide-bound [14C]diferuloyl residues were a steady 1.4% of the total polysaccharide-bound [14C]ferulate derivatives. In contrast to the situation in younger cultures, exogenous H2O2 induced a rapid 4- to 6-fold increase in all coupling products, indicating that coupling in the walls was H2O2-limited. In both 2- and 4-d-old cultures, polysaccharide-bound 14C-trimers and larger coupling products exceeded [14C]diferulates 3- to 4-fold, but followed similar kinetics. Thus, although all known dimers of ferulate can now be individually
quantified, it appears to be trimers and larger products that make the major contribution to cross-linking of wall polysaccharides
in cultured maize cells. We argue that feruloyl arabinoxylans that are cross-linked before and after secretion are likely
to loosen and tighten the cell wall, respectively. The consequences for the control of cell expansion and for the response
of cell walls to an oxidative burst are discussed.
Received: 19 January 2000 / Accepted: 13 April 2000 相似文献
17.
G Soman M O Hurst D J Graves 《International journal of peptide and protein research》1985,25(5):517-525
The role of structural features and deprotonation of guanidino derivatives on chemical reactions with p-nitrophenylglyoxal has been investigated. Canavanine, an arginine analog, reacts to form a yellow product, which absorbs maximally at 350 nm (epsilon = 6500) and at 278 nm (epsilon = 14 500). Elemental analysis, fast atom bombardment mass spectral analysis, n.m.r. and i.r. studies suggest that the product is a 5-(p-nitrophenyl)4-oxo-2 imidazoline derivative of canalaline. Kinetic studies show that the second order rate constant for the reaction increases with increasing pH in the range of pH 7-11.0. It is concluded that the pH dependence of the reaction can be explained by general base catalysis and not simply by a deprotonation of the guanidinoxy side chain. The reaction of arginine, polyarginine, and other derivatives differs markedly from that of canavanine. The results suggest that change in the tautomeric equilibria between the imino and amino forms of the guanidino group may partly account for differences in reaction of canavanine and arginine and the reactions of specific arginyl residues in proteins. 相似文献
18.
Alessandro Moretto Marta De Zotti Marco Crisma Fernando Formaggio Claudio Toniolo 《International journal of peptide research and therapeutics》2008,14(4):307-314
“Mono-N-methyl scan” is a rational approach for the optimization of the peptide biological properties. N-Methylation of the –CONH– functionality is also a useful tool for discriminating solvent exposed from intramolecularly H-bonded
secondary amide groups in peptides. We are currently extending this reaction to linear peptides based on Cα-tetrasubstituted α-amino acids. Following our study on the synthesis and conformation of the mono-N-methylated peptides from Cα-methylated residues, in this work we investigated the N-methylation reaction on homo-peptides to the pentamer level from the Cα-ethylated residue Cα,α-diethylglycine. Under the classical experimental conditions used, exclusively mono-N-methylation (on the N-terminal, acetylated residue) takes place, as unambiguously shown by mass spectrometry, 2D-NMR, and X-ray diffraction techniques.
This backbone modification does not seem to involve any significant change in the peptide conformation in the crystalline
state.
Dedicated to the memory of Prof. Miroslav T. Leplawy (Technical University of Łodz, Poland), who performed the first synthesis
of the extremely sterically demanding Cα,α-diethylglycine peptides. 相似文献
19.
Summary. An assessment of the potential of proline to scavenge free radicals was made in a couple of in vitro assay systems, namely
graft co-polymerization and autooxidation of pyrogallol. Both these assays are essentially dependent upon free radical mechanisms.
Graft co-polymerization involved a ceric (Ce4+) ion- or γ-radiation-induced grafting of methyl acrylate (MA) onto a cellulose backbone. The degree of grafting, measured
gravimetrically, was taken as a measure of free radical generation. The γ-radiation-dependent grafting was far greater than
that due to Ce4+ ions. Inclusion of proline in the assay, irrespective of the initiator used, led to suppression of grafting in a concentration-dependent
manner indicating the ability of proline to scavenge free radicals. The γ-radiation-dependent grafting was also suppressed
by hydroquinone and glutathione but not by ascorbate, glycine and spermine. In contrast to graft co-polymerization, proline
did not inhibit the autooxidation of pyrogallol, a reaction involving superoxide radical generation. A subset of data constitutes
an evidence for the ability of proline to scavenge free radicals in vitro. It is implied by extension that free proline, known
to accumulate in plant tissues during abiotic stresses, would contribute to scavenging of surplus free radicals produced under
a variety of abiotic stresses.
Authors’ address: Shanti S. Sharma, Department of Biosciences, Himachal Pradesh University, Shimla 171 005, India 相似文献
20.
Almost all about citrulline in mammals 总被引:2,自引:0,他引:2
Curis E Nicolis I Moinard C Osowska S Zerrouk N Bénazeth S Cynober L 《Amino acids》2005,29(3):177-205
Summary. Citrulline (Cit, C6H13N3O3), which is a ubiquitous amino acid in mammals, is strongly related to arginine. Citrulline metabolism in mammals is divided
into two fields: free citrulline and citrullinated proteins. Free citrulline metabolism involves three key enzymes: NO synthase
(NOS) and ornithine carbamoyltransferase (OCT) which produce citrulline, and argininosuccinate synthetase (ASS) that converts
it into argininosuccinate. The tissue distribution of these enzymes distinguishes three “orthogonal” metabolic pathways for
citrulline. Firstly, in the liver, citrulline is locally synthesized by OCT and metabolized by ASS for urea production. Secondly,
in most of the tissues producing NO, citrulline is recycled into arginine via ASS to increase arginine availability for NO
production. Thirdly, citrulline is synthesized in the gut from glutamine (with OCT), released into the blood and converted
back into arginine in the kidneys (by ASS); in this pathway, circulating citrulline is in fact a masked form of arginine to
avoid liver captation. Each of these pathways has related pathologies and, even more interestingly, citrulline could potentially
be used to monitor or treat some of these pathologies. Citrulline has long been administered in the treatment of inherited
urea cycle disorders, and recent studies suggest that citrulline may be used to control the production of NO. Recently, citrulline
was demonstrated as a potentially useful marker of short bowel function in a wide range of pathologies. One of the most promising
research directions deals with the administration of citrulline as a more efficient alternative to arginine, especially against
underlying splanchnic sequestration of amino acids. Protein citrullination results from post-translational modification of
arginine; that occurs mainly in keratinization-related proteins and myelins, and insufficiencies in this citrullination occur
in some auto-immune diseases such as rheumatoid arthritis, psoriasis or multiple sclerosis. 相似文献