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1.
Summary. A novel practical method for the synthesis of N-methyl-DL-aspartic acid 1 (NMA) and new syntheses for N-methyl-aspartic acid derivatives are described. NMA 1, the natural amino acid was synthesized by Michael addition of methylamine to dimethyl fumarate 5. Fumaric or maleic acid mono-ester and -amide were regioselectively transformed into beta-substituted aspartic acid derivatives.
In the cases of maleamic 11a or fumaramic esters 11b, the α-amide derivative 13 was formed, but hydrolysis of the product provided N-methyl-DL-asparagine 9 via base catalyzed ring closure to DL-α-methylamino-succinimide 4, followed by selective ring opening. Efficient methods were developed for the preparation of NMA-α-amide 13 from unprotected NMA via sulphinamide anhydride 15 and aspartic anhydride 3 intermediate products. NMA diamide 16 was prepared from NMA dimethyl ester 6 and methylamino-succinimide 4 by ammonolysis. Temperature-dependent side reactions of methylamino-succinimide 4 led to diazocinone 18, resulted from self-condensation of methylamino-succinimide via nucleophyl ring opening and the subsequent ring-transformation. 相似文献
2.
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
3.
Kottakis F Lamari F Matragkou Ch Zachariadis G Karamanos N Choli-Papadopoulou T 《Amino acids》2008,34(3):413-420
Summary. Arabino-Galactan Proteins (AGPs) were isolated from Chios mastic gum (CMG) by using a buffer containing 0.1 M NaCl, 20 mM
Tris–HCl, pH 7.5. Protein analytical methods, combined with specific procedures for carbohydrate characterization, indicated
the presence of highly glycosylated protein backbone. In particular, staining by Yariv reagent of the electrophoretically
separated molecules revealed the existence of arabinose and galactose and such a modification is characteristic for AGPs.
After experiments involving extensive dialysis of the isolated extracts against water and atomic absorption, there was evidence
of the existence of zinc ions that are probably covalently bound to the AGPs. By using anion-exchange chromatography, capillary
electrophoresis, colorimetric methods and GC-MS, it was found that the extracts were separated into three major populations
(A, B, and C), which were consistent with their respective negative charge content namely, uronic acid. The characterization
of neutral sugars that was investigated with GC-MS showed the existence of arabinose and galactose in different amounts for
each group.
Experiments concerning the inhibition of growth of Helicobacter pylori in the presence of AGPs, as is shown for other CMG constituents, showed that the extracts of at least 1.4 g CMG affected
the viability of the bacterium. There is no evidence as to whether the AGPs provoke abnormal morphologies of H. pylori, as is reported for the total CMG, or for O-glycans that possess terminal α1, 4-linked N-acetylglucosamine and are expressed
in the human gastric mucosa; this has to be further investigated.
Authors’ address: Theodora Choli-Papadopoulou, Laboratory of Biochemistry, School of Chemistry, Aristotle University of Thessaloniki,
TK 54124 Thessaloniki, Greece 相似文献
4.
Summary. Hydrogensquarates of dipeptide l-threonyl-l-serine (H-Thr-Ser-OH) and l-serine (HSq × Ser) have been synthesized, isolated and spectroscopic characterized by solid-state linear-polarized IR-spectroscopy, 1H- and 13C-NMR, ESI-MS and HPLC with tandem masspectrometry (MS-MS) methods. The structures of the salts and neutral dipeptide have
been predicted theoretically by ab initio calculations. In the case of H-Thr-Ser-OH the theoretical data are supported by IR-LD ones. The hydrogensquarates consist in positive charged dipeptide or amino acid
moiety and negative hydrogensquarate anion (HSq) stabilizing by strong intermolecular hydrogen bonds. The data about the l-serine hydrogensquarate are compared with known crystallographic data thus indicating a good correlation between the theoretical
predicted structures and experimentally obtained by single crystal X-ray diffraction. 相似文献
5.
Summary. Ornithine decarboxylase (ODC) has a very fast turnover in mammalian cells, but is a stable enzyme in T. brucei and other trypanosmatid parasites like Leishmania donovani. However, Crithidia fasciculata, which is a phylogenetically closely related trypanosomatid to L. donovani, has an ODC with a rapid turnover. Interestingly, C. fasciculata ODC, but not L. donovani ODC, is rapidly degraded also in mammalian systems. In order to obtain information on what sequences are important for the
rapid degradation of C. fasciculata ODC, we produced a variety of C. fasciculata/L. donovani ODC hybrid proteins and characterized their turnover using two different mammalian expression systems. The results obtained
indicate that C. fasciculata ODC contains several sequence elements essential for the rapid turnover of the protein and that these regions are mainly
located in the central part of the enzyme.
Present address: Department of Microbiology, Moyne Institute of Preventive Medicine, University of Dublin – Trinity College,
Dublin, Ireland
Authors’ address: Lo Persson, Department of Experimental Medical Science, Lund University, BMC D-12, S-221 84 Lund, Sweden 相似文献
6.
Oshima T 《Amino acids》2007,33(2):367-372
Summary. Recent research progress on polyamines in extreme thermophiles is reviewed. Extreme thermophiles produce two types of unique
polyamines; one is longer polyamines such as caldopentamine and caldohexamine, and the other is branched polyamines such as
tetrakis(3-aminopropyl)ammonium. The protein synthesis catalyzed by a cell-free extract of Thermus thermophilus, an extreme thermophile, required the presence of a polyamine and the highest activity was found in the presence of tetrakis(3-aminopropyl)ammonium.
In vitro experiments, longer polyamines efficiently stabilized double stranded nucleic acids and a branched polyamine, tetrakis(3-aminropyl)ammonium,
stabilized stem-and-loop structures. In T. thermophilus, polyamines are synthesized from arginine by a new metabolic pathway; arginine is converted to agmatine and then agmatine
is aminopropylated to N1-aminopropylagmatine which is converted to spermidine by an enzyme coded by a gene homologous to speB (a gene for agmatinase). In this new pathway spermidine is not synthesized from putrescine. Reverse genetic studies indicated
that the unique polyamines are synthesized from spermidine. 相似文献
7.
Torres AM Tsampazi M Kennett EC Belov K Geraghty DP Bansal PS Alewood PF Kuchel PW 《Amino acids》2007,32(1):63-68
Summary. Platypus venom contains an isomerase that reversibly interconverts the second amino-acid residue in some peptides between
the L-form and the D-form. The enzyme acts on the natriuretic peptides OvCNPa and OvCNPb, and on the defensin-like peptides DLP-2 and DLP-4, but
it does not act on DLP-1. While the isomerization of DLP-2 to DLP-4 is inhibited by the amino-peptidase inhibitor amastatin,
it is not affected by the leucine amino-peptidase inhibitor bestatin. The enzyme, that is only present in minute quantities
in an extract of the venom gland, is thermally stable up to 55 °C, and it was found by anion-exchange chromatography to be
acidic. Isolation of the isomerase was carried out by combined ion-exchange chromatography and reverse-phase high performance
liquid chromatography (HPLC). 相似文献
8.
Summary.
Chlamydomonas reinhardtii, a unicellular green microalga, could grow to a stationary phase having optical density of 2.0–2.5 at 750 nm in Tris-acetate-phosphate
(TAP) medium containing 0.1% D-alanine. D-alanine has no inhibitory effect on growth and induced alanine racemase activity
130-fold more than without D-alanine in the green alga. Although C. reinhardtii cultured in the TAP medium showed alanine racemase activity, the content of free D-alanine was only 0.14%. The enzyme was
partially purified by ammonium sulfate fractionation followed by three kinds of liquid chromatography using DEAE Toyopearl,
Phenyl Sepharose, and TSK G3000 SWXL columns. The specific activity for L-alanine of the partially purified alanine racemase
was 3.8 μmol/min/mg. The molecular weight of the enzyme was determined to be approximately 72,000 by gel filtration. The enzyme
showed a maximum activity at 45 °C and pH 8.4 and requires pyridoxal 5′-phosphate as a coenzyme. 相似文献
9.
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
10.
Summary. Protein L4 from the thermophilic bacterium Thermus thermophilus (TthL4) was heterologously overproduced in Escherichia coli cells and purified under native conditions by using ion exchange chromatography. Although it’s known strong binding to RNA
(23S rRNA as well as mRNA) the yield of the purified protein was 6 mg per 10 g of cells and it is similar to that referred
for Thermotoga maritima L4 ribosomal protein.
In addition, E. coli cells harboring the wild type Thermus thermophilus L4 (wtTthL4) ribosomal protein as well as its mutant having changed the highly conserved glutamic acid 56 by alanine (TthL4-Ala
56) were incorporated into E. coli ribosomes after transformation of the host cells with the recombined vector. The cells having incorporated the mutant TthL4-Ala56
are more sensitive against erythromycin related to that containing the wtTthL4 protein.
The resistance to the drug indicates that the mutated amino acid Glu56 is probably critical for the local ribosomal conformation
and that its mutation induces conformational disturbances that are “transferred” to the entrance of the major exit tunnel,
the place where the drug does bind. 相似文献
11.
Summary. Mammalian hexokinase (HXK) is found at the outer mitochondrial membrane, exposed to mitochondrial oxygen- and nitrogen-radicals.
Given the important role of this enzyme in metabolic pathways and diseases, the effect of S-nitrosoglutathione (GSNO) on HXK A structure and activity was studied. To focus on the catalytic domain, yeast HXK A was
used because it has a significant homology to the mammalian domain that contains both the regulatory and catalytic sites.
Biologically relevant [GSNO]/[HXK] caused a significant decrease in Vmax with glucose (but not with fructose), along with oxidation of 5 Met and nitration of 4 Tyr. Preincubation of HXK with glucose
abrogated the effect of GSNO whereas fructose was ineffective. These results are interpreted by considering the tight binding
of glucose to the enzyme as opposed to that of fructose. The segment comprised from amino acids 304 to 306 contained the most
modifications. Given that this sequence is highly conserved in HXK from various species, a decline in activity is expected
when a high-affinity substrate is presented.
Considering that changes in primary structure are envisioned at high [GSNO]/[HXK] ratios, like those present under normal
conditions, it could be hypothesized that the high concentration of hexokinase present in fast growing tumors may serve not
only to sustain high glycolysis rates, but also to minimize protein damage that might result in activity decline, compromising
energy metabolism. 相似文献
12.
Summary. Optically pure (S)-3-p-hydroxyphenyllactic acid derivatives are important intermediates of peroxisome proliferator-activated receptor α/γ dual agonists
and heteropeptides. Many efforts have been made for synthesis of those intermediates, but there exist some flaws yet. We observed
that dielectric constants of organic solvents drastically affected diazotization of O-benzyl-L-tyrosine. Optically pure (S)-3-p-benzyloxyphenyllactic acid was obtained by simple recrystallization when DMF or DMSO of higher dielectric constant was used
as a co-solvent in diazotization of O-benzyl-L-tyrosine. It was easily turned into various optically pure (S)-3-p-hydroxyphenyllactic acid derivatives. 相似文献
13.
The relationship between Sporidiobolus johnsonii and S. salmonicolor was investigated using rDNA sequence data. Two statistically well-supported clades were obtained. One clade included the
type strain of S. johnsonii and the other included the type strain of S. salmonicolor. However, some mating strains of S. salmonicolor were found in the S. johnsonii group. These strains belonged to mating type A2 and were sexually compatible with mating type A1 strains from the S. salmonicolor group. DNA–DNA reassociation values were high within each clade and moderate between the two clades. In the re-investigation
of teliospore germination, we observed that the basidia of S. salmonicolor were two-celled. In S. johnsonii, basidia were not formed and teliospore germination resulted in direct formation of yeast cells. We hypothesize that the
S. johnsonii clade is becoming genetically isolated from the S. salmonicolor group and that a speciation process is presently going on. We suspect that the observed sexual compatibility between strains
of the S. johnsonii and S. salmonicolor groups and the possible genetic flow between the two species has little biological relevance because distinct phenotypes
have been fixed in the two taxa and intermediate (hybrid) sequences for LSU and ITS rDNAs have not been detected.
An erratum to this article can be found at 相似文献
14.
Summary. The 1-(N-trifluoroacetylamino)alkylphosphonic acids (TFA-AAP) – sub-products in the synthesis of O,O-dialkyl 1-(N-trifluoroacetylamino)alkylphosphonates and O,O-diethyl 1-aminoalkylphosphonates, were synthesized in two-stage transformations of 1-aminoalkylphosphonic acids including:
trifluoroacetylation of 1-aminoalkylphosphonic acids (AAP) using a trifluoroacetic anhydride/trifluoroacetic acid reagent (AAP + TFAA/TFA→2) and subsequent hydrolysis of the intermediary compounds 2 into desired TFA-AAP (2→TFA-AAP). These intermediates 2 presented mixtures of the type of mixed anhydrides of TFAA and 1-(N-trifluoroacetylamino)alkylphosphonic, pyrophosphonic and polyphosphonic acids, which underwent rapid and quantitative conversion
to corresponding TFA-AAP during treatment with an excess of water. The title acids were isolated by direct evaporation of the corresponding post-reaction
mixtures, and their physicochemical proprieties, including deacylation abilities, were determined. TFA-AAP compounds can be re-converted into the starting amino acids AAP under respectively mild conditions (AAP→TFA-AAP→AAP). 相似文献
15.
Summary. Branched-chain amino acid aminotransferase was purified by several column chromatographies from Helicobacter pylori NCTC 11637, and the N-terminal amino acid sequence was analyzed. The enzyme gene was sequenced based on a putative branched-chain
amino acid aminotransferase gene, ilvE of H. pylori 26695, and the whole amino acid sequence was deduced from the nucleotide sequence. The enzyme existed in a homodimer with
a calculated subunit molecular weight (MW) of 37,539 and an isoelectric point (pI) of 6.47. The enzyme showed high affinity
to 2-oxoglutarate (K
m = 0.085 mM) and L-isoleucine (K
m = 0.34 mM), and V
max was 27.3 μmol/min/mg. The best substrate was found to be L-isoleucine followed by L-leucine and L-valine. No activity was
shown toward the D-enantiomers of these amino acids. The optimal pH and temperature were pH 8.0 and 37 °C, respectively. 相似文献
16.
Summary. The major enzyme of the methionine sulfoxide reductase (Msr) system is MsrA. Senescing msrA knockout mother yeast cells accumulated significant amounts of protein-carbonyl both at 5 generation-old (young) and 21 generation-old
(old) cultures, while the control mother cells showed significant levels of protein-carbonyl mainly in the old culture. The
Msr activities of both yeast strains declined with age and exposure of cells to H2O2 caused an accumulation of protein-carbonyl especially in the msrA knockout strain. It is suggested that a compromised MsrA activity may serve as a marker for non-replicative aging. 相似文献
17.
Fish in aquaculture are often exposed to various stressors that may change their ability to survive or limit growth. Amino acids are used for processes other than growth, including stress response. This study intended to analyse how repeated acute handling stress can affect growth and amino acid requirements in fish. Senegalese sole juveniles were weekly held in the air during 3 min (Handling) for 9 weeks; Control groups were left undisturbed. Growth and plasma levels of stress indicators and of free amino acids were assessed at the end of the experiment. Plasma cortisol and osmolality levels showed that fish in the Handling treatment were stressed, but growth was unaffected. Plasma amino acid concentrations indicate that their requirements in stressed fish were altered, which probably reflects the synthesis of proteins or other specific compounds related to stress response. 相似文献
18.
Summary. Induction of heat shock protein (Hsp) 70 and distinct metallothionein-like proteins (MTLPs) in response to Cd and heat treatment
were studied in two strains of the aquatic hyphomycete Heliscus lugdunensis: Hl-H4, isolated from a heavy metal polluted site, and Hl-BB taken from an unpolluted area. Upon Cd-exposure, Hsp70 was actively
synthesized in the strain Hl-H4, and to a much lower degree in the strain Hl-BB. The Hsp70-expression was time- and dose-dependent,
reaching a maximum after 24 h incubation with 80 μM Cd. Upon heat-stress, a similar response was observed: a strong Hsp70-expression
in Hl-H4, and only a marginal one in Hl-BB. The strains reacted to Cd-exposure by a specific, environmentally related induction
of MTLPs, as shown by the highly sensitive bimane derivatisation method of SH-rich proteins. In Hl-H4, a strong expression
of 11 kDa MTLP was registered, which followed strictly the induction pattern of Hsp70. This suggests interdependence of the
induction mechanisms and roles of these stress proteins in metal resistance. On the contrary, in Hl-BB a weak expression of
MTLP of about 20 kDa was observed, exhibiting completely different induction pattern. The results suggest that the specific
induction of Hsp70 and/or distinct MTLPs in the range of 11 kDa in H. lugdunensis strain Hl-H4 are essential adaptive mechanisms to continuous heavy metal exposure.
Authors’ address: Assoc. Prof. Dr. Konstantin Grancharov, Bulgarian Academy of Sciences, Institute of Molecular Biology, Acad.
G. Bonchev Str. Bl. 21, BG-1113 Sofia, Bulgaria 相似文献
19.
Crop to weed transgene flow, which could result in more competitive weed populations, is an agricultural biosafety concern.
Crop Brassica napus to weedy Brassica rapa hybridization has been extensively characterized to better understand the transgene flow and its consequences. In this study,
weedy accessions of B. rapa were transformed with Bacillus thuringiensis (Bt) cry1Ac- and green fluorescence protein (gfp)-coding transgenes using Agrobacterium to assess ecological performance of the wild biotype relative to introgressed hybrids in which the transgenic parent was
the crop. Regenerated transgenic B. rapa events were characterized by progeny analysis, Bt protein enzyme-linked immunosorbent assay (ELISA), Southern blot analysis,
and GFP expression assay. GFP expression level and Bt protein concentration were significantly different between independent
transgenic B. rapa events. Similar reproductive productivity was observed in comparison between transgenic B. rapa events and B. rapa × B. napus introgressed hybrids in greenhouse and field experiments. In the greenhouse, Bt transgenic plants experienced significantly
less herbivory damage from the diamondback moth (Plutella xylostella). No differences were found in the field experiment under ambient, low, herbivore pressure. Directly transformed transgenic
B. rapa plants should be a helpful experimental control to better understand crop genetic load in introgressed transgenic weeds. 相似文献
20.
A new species of Erysiphe sect. Uncinula is described and illustrated from Patagonia, Argentina. Erysiphe patagoniaca sp. nov., found on leaves of Nothofagus × antarctica, is similar to E. nothofagi and E. kenjiana, but differs in its appendages being twisted throughout their length and the number of appendages, asci, and ascospores.
The two endemic species of Erysiphe sect. Uncinula, E. magellanica and E. nothofagi, coexisted on the same leaves together with Erysiphe patagoniaca.
Received: September 19, 2002 / Accepted: November 28, 2002
Acknowledgments The authors are grateful to Ms. Seiko Niinomi for providing the micrographs of ascomata of Erysiphe spp. on Nothofagus.
Correspondence to:S. Takamatsu 相似文献