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PubMed1977

Increased oxygen affinity for hemoglobin Sawara: alphaA4(6) aspartic acid replaced by alanine.

The oxygen binding property of Hb Sawara (alphaA4 Asp replaced by Ala) was studied at different pH values with and without addition of 2,3-diphosphoglycerate. The oxygen affinity of Hb Sawara was shown to be increased, the difference of the log P50 value between normal and abnormal hemoglobins being 0.37 at pH 7.0. Both the magnitude of the alkaline Bohr effect and the effect of 2,3-diphosphoglycerate upon oxygen affinity of Hb Sawara were comparable to those of Hb A. The amino acid substitution of alanine for alphaA4 aspartic acid might result in the loss of a stabilizing force for ionic interaction between the alpha-amino group of NA (1)alpha1 valine and the alpha-carboxyl of HC3(141)alpha2 arginine in the deoxy-form.

Alanine↗
PubMed1987

The occurrence of N-methyl-D-aspartic acid in muscle extracts of the blood shell, Scapharca broughtonii.

A novel ninhydrin-positive compound, N-methyl-D-aspartic acid, was identified in the muscle extracts of the blood shell, Scapharca broughtonii. This compound is already known to have potent neuroexcitatory activity, inducing hypermotility and strong releasing action of serum luteinizing hormone in mammals. This may be, however, the first finding of N-methyl-D-aspartic acid in natural products.

Animals↗
PubMed2005

Possible involvement of glutamic and/or aspartic acid residue(s) and requirement of mitochondrial integrity for the protective effect of creatine against inhibition of cardiac mitochondrial respiration by methylglyoxal.

We had previously shown that creatine exerted a protective effect against inhibition of cardiac mitochondrial respiration by methylglyoxal (SinhaRoy S, Biswas S, Ray M, Ray S. Biochem J 372: 661-669,2003). In the present study, we have investigated the mechanism of this protective effect by specific amino acid modifying reagent and by several compounds, which are structurally related to creatine. The results show that the compounds, which contain guanidine group such as arginine and guanidinopropionic acid, exert a protective effect, which is quantitatively similar to creatine. This result suggests the presence of carboxylic acid(s) such as glutamic and/or aspartic acid(s) in the creatine-binding site, which has been further supported by experiments with N-ethyl-5-phenyl isoxazolium-3'-sulfonate a reagent known to modify these amino acids. Both polarographic and spectrophotometric assays were performed with NADH as respiratory substrate by using a) submitochondrial particles by sonication, b) freeze-thawed mitochondria and c) mitochondria permeabilized by alamethicin treatment. The results of these studies as compared to that of intact mitochondria indicate that structural integrity of mitochondria is essential for the protective effect of creatine.

Alamethicin↗
PubMed1996

Effects of mutagenesis of aspartic acid residues in the putative phosphoribosyl diphosphate binding site of Escherichia coli phosphoribosyl diphosphate synthetase on metal ion specificity and ribose 5-phosphate binding.

The three conserved aspartic acid residues of the 5-phospho-D-ribosyl alpha-1-diphosphate binding site (213-GRDCVLVDDMIDTGGT-228) of Escherichia coli phosphoribosyl diphosphate synthetase were studied by analysis of the mutant enzymes D220E, D220F, D221A, D224A, and D224S. The mutant enzymes showed an increase in KM for ribose 5-phosphate in the presence of at least one of the divalent metal ions Mg2+, Mn2+, Co2+, or Cd2+, with the most dramatic changes revealed by the D220E and D220F enzymes in the presence of Co2+ and the D221A enzyme in the presence of Mn2+ or Co2+. The D220F and D221A enzymes both showed large decreases in Vapp in the presence of the various divalent metal ions, except for the D221A enzyme in the presence of Co2+. Vapp of the D220E enzyme was similar to that of the wild-type enzyme in the presence of Mg2+, Mn2+, or Cd2+, whereas the Vapp was increased in the presence of Co2+. Vapp values of the D224A and D224S enzymes were lowered to 10-15-fold and 3-4-fold in the presence of Mg2+ or Mn2+, respectively, whereas Vapp was similar to that of the wild-type and KM for Rib-5-P was increased 4-fold in the presence of Cd2+. The changes in KM for ribose 5-phosphate and Vapp of the mutant enzymes were dependent on the metal ion present, suggesting a function of the investigated aspartic acid residues both in the binding of ribose 5-phosphate, possibly via a divalent metal ion, and in the interaction with a divalent metal ion during catalysis.

Amino Acid Sequence↗
PubMed1989

Qualitative changes in luteinizing hormone and prolactin responses to N-methyl-aspartic acid during lactation in the rat.

The suppression during lactation of pulsatile LH release and pituitary GnRH receptors has been attributed to a primary deficit in hypothalamic GnRH release. In the present investigation we have attempted to characterize the responsiveness of the lactational hypothalamus using the excitatory amino acid receptor agonist N-methyl-aspartic acid (NMA) to stimulate LH and PRL secretion. Lactating rats were ovariectomized on day 2 postpartum, and their litters were adjusted to eight pups. Dual venous catheters were implanted 6-7 days later, and rats were fitted with protective tethers and jackets for chronic pulsatile infusions of GnRH and NMA. GnRH pulses (5 or 10 ng/pulse once every 50 min) were administered for 20 h to up-regulate GnRH receptors and restore pituitary responsiveness to GnRH. Rats were then infused with NMA (40 mg/kg BW.pulse) once every 50 min for four pulses or once every 2 h over a 24-h period. Blood samples were collected at 10-min intervals at times surrounding the final two GnRH pulses, the first several NMA pulses, and the final three NMA pulses 24 h later. Samples were analyzed for LH and PRL by RIA. Procedural control experiments were performed in normal adult rats with NMA administered at 20 mg/kg BW.pulse in males and at 20 and 40 mg/kg BW.pulse in females. Whereas normal rats responded to NMA pulses with unambiguous LH and PRL peaks, lactating rats failed to show LH responses either acutely or after 24 h of treatment. PRL responses to the drug depended upon the circulating levels of the hormone immediately preceding each NMA pulse. When levels were elevated (presumably due to intermittent suckling by the pups), NMA infusion resulted in an acute suppression of PRL. When PRL levels were low, NMA appeared to neither stimulate nor inhibit this hormone. These data suggest that GnRH release from the hypothalamus of the lactating rat is refractory to NMA stimulation, perhaps due to suckling-induced activation of endogenous opioid peptide or gamma-aminobutyric acid systems that could suppress GnRH neurons. Conversion of the PRL response from stimulation by NMA in normal animals to inhibition during lactation might be attributed to simultaneous activation of both dopamine neurons and the PRL-releasing factor system. According to this hypothesis, the response to NMA would be dominated by PRL-releasing factor in normal rats and by dopamine in lactating animals, which have a lower dopamine turnover rate and thus a greater potential for becoming activated by NMA.

Animals↗
PubMed1975

An asparagine requirement in young rats fed the dietary combinations of aspartic acid, glutamine, and glutamic acid.

The effect of dietary asparagine on rat growth was investigated. Diets were formulated with L-amino acids so as to contain asparagine, aspartic acid, glutamine and/or glutamic acid in all possible combinations and then fed to weanling rats for 3 weeks. Of the four, only asparagine was found to be essential for optimal growth, and it was essential regardless of the presence or absence of any dietary combination of these related amino acids. In selected dietary groups, the unbound asparagine levels were measured in various tissues over an 8-day period. Muscle asparagine levels were reduced for asparagine-deprived animals over the entire period studied; brain levels were decreased only after 7 days of dietary depletion, while hepatic levels were unaffected by dietary asparagine deprivation. In a related series, animals were more drastically depleted of asparagine by combining dietary deprivation with asparaginase treatment, causing a rapid decrease in cellular concentration of asparagine, which affected protein and DNA synthesis for those organs undergoing hyperplastic growth. Thus, asparagine may be rate limiting to protein synthesis for this extreme case as well as during dietary asparagine deprivation, which also decreased intracellular levels of unbound asparagine and led to irreversible deficits in development.

Animal Nutritional Physiological Phenomena↗
PubMed1981

Immobilization of Escherichia coli Cells Containing Aspartase Activity with Polyurethane and Its Application for l-Aspartic Acid Production.

Whole cells of Escherichia coli containing aspartase activity were immobilized by mixing a cell suspension with a liquid isocyanate-capped polyurethane prepolymer (Hypol). The immobilized cell preparation was used to convert ammonium fumarate to l-aspartic acid. Properties of the immobilized E. coli cells containing aspartase were investigated with a batch reactor. A 1.67-fold increase in the l-aspartic acid production rate was observed at 37 degrees C as compared to 25 degrees C operating temperature. The pH optimum was broad, ranging from 8.5 to 9.2. Increasing the concentration of ammonium fumarate to 1.5 M from 1.0 M negatively affected the reaction rate. l-Aspartic acid was produced at an average rate of 2.18 x 10 mol/min per g (wet weight) of immobilized E. coli cells with a 37 degrees C substrate solution consisting of 1.0 M ammonium fumarate with 1 mM Mg (pH 9.0).

Journal Article↗
PubMed1990

Synthesis of beta- and gamma-fluorenylmethyl esters of respectively N alpha-Boc-L-aspartic acid and N alpha-Boc-L-glutamic acid.

The orthogonal synthesis of N alpha-Boc-L-aspartic acid-gamma-fluorenylmethyl ester and N alpha-Boc-L-glutamic acid-delta-fluorenylmethyl ester is reported. This is a four-step synthesis that relies on the selective esterification of the side-chain carboxyl groups on N alpha-CBZ-L-aspartic acid and N alpha-CBZ-L-glutamic acid. Such selectivity is accomplished by initially protecting the alpha-carboxyl group through the formation of the corresponding 5-oxo-4-oxazolidinone ring. Following side-chain esterification, the alpha-carboxyl and alpha-amino groups are deprotected with acidolysis. Finally, the alpha-amino group is reprotected with the t-butyl-oxycarbonyl (Boc) group. Thus aspartic acid and glutamic acid have their side-chain carboxyl groups protected with the base-labile fluorenylmethyl ester (OFm) and their alpha-amino groups protected with the acid-labile Boc group. These residues, when used in conjunction with N alpha-Boc-N epsilon-Fmoc-L-lysine, are important in the formation of side-chain to side-chain cyclizations, via an amide bridge, during solid-phase peptide synthesis.

Aspartic Acid↗
PubMed1981

Uptake of leucine, lysine, aspartic acid, and glycine into isolated neurons and astrocytes.

The uptake of tritium-labeled L-leucine, L-lysine, L-aspartic acid, and glycine by neurons and astrocytes isolated from the cerebral cortex of 3-week-old rats was followed for varying periods up to 40 min at amino acid concentrations from 1 to 2000 micromol/liter in medium. The effects of a low-sodium (15.5 mmol/liter) medium on the uptake were also studied. The influx of the amino acids was faster into astrocytes than into neurons. Leucine penetrated into the cells faster than the other amino acids. Amino acids transport was mainly saturable at the lowest amino acid concentrations studied, whereas nonsaturable penetration into the cells dominated in the millimolar concentration range. The saturable transport comprised only one transport system with relatively small transport constants, resembling in nature the so-called high-affinity transport. The maximal velocities of transport were about two times higher in astrocytes than in neurons. In neurons the partial substitution of sodium by choline in medium had the most effect in reducing the influx of glycine and aspartic acid. In astrocytes the effects were generally less pronounced. The results suggest that extracellular amino acids generally penetrate more readily into astrocytes than into neurons. Both cell types transport essential amino acids more effectively than other amino acids.

Animals↗
PubMed1997

Effects of mutations of aspartic acid 63 on the metal-binding properties of the recombinant N-lobe of human serum transferrin.

Mutations of the aspartic acid residue at position 63 of the N-lobe of human serum transferrin substantially alter the metal ion- and anion-binding properties of the protein. Substitution of serine, asparagine, glutamic acid, or alanine results in the loss of a key component of the interface in the interdomain cleft and the metal-binding ligand, aspartic acid, leading in all cases to an increased preference for NTA rather than carbonate as the "synergistic" anion relative to the wild-type protein. Excess bicarbonate is required to eliminate the NTA and obtain the "correct" visible spectrum. Carbonate replaces NTA via an intermediate. Blue shifts for the characteristic absorption band of each mutant show a range of effects on the Fe-O (Tyr) interaction. Titration with Co(III) yielded the molecular absorption coefficient for each mutant except D63A, where Co(III) appeared to oxidize the tyrosine residues and damage the ability of the mutant to bind metal. The chelator, Tiron, removes iron from hTF/2N with a simple saturation kinetic mode with respect to the ligand concentration. Chloride inhibits the release in an interesting manner: the effect is initially sharp and then levels off with a minimum k(obs) at [KCl] = 0.5 M. However, the reaction of the D63 mutants with Tiron results in the formation of the ternary complexes Fe-hTF/2N-Tiron. Significant red shifts for the characteristic absorption bands of these complexes suggest a different ligation of Tiron in the mutants from that in wild-type hTF/2N.

Aspartic Acid↗
PubMed1978

Modification of aspartic acid residues to induce trypsin cleavage.

1,2-Diaminoethane and diaminomethane were coupled to aspartic acid residues in small peptides by means of a water-soluble carbodiimide. The resulting modified side chains sufficiently resembled lysine for trypsin to cleave the peptides. Similar modification of glutamic acid residues in peptides gave little or no susceptibility to trypsin.

Amino Acid Sequence↗
PubMed2003

Pathogenesis of coxsackievirus A9 in mice: role of the viral arginine-glycine-aspartic acid motif.

Coxsackievirus A9 (CAV9) contains an arginine-glycine-aspartic acid (RGD) motif which participates in cell entry. Mutants with alterations in the RGD-containing region were utilized to explore the importance of the tripeptide in the pathogenesis of CAV9 in mice. Using in situ hybridization, the parental CAV9 strain was observed to infect skeletal muscle (intercostal, platysma, lingual and thigh muscles) of newborn mice, whereas the RGD-less mutants were detectable only in platysma and lingual muscles. In addition, newborn mice infected with the mutants survived longer than CAV9-infected mice. In adult mice, the parental strain of CAV9, but not the mutants, achieved moderately high titres in the pancreas. These results suggest that the RGD motif has a significant role in the pathogenesis of CAV9 in mice but also that RGD-independent entry routes can be utilized in the infection of murine tissue.

Amino Acid Motifs↗
PubMed2001

Substrate translocation kinetics of excitatory amino acid carrier 1 probed with laser-pulse photolysis of a new photolabile precursor of D-aspartic acid.

Here we report the synthesis and photochemical and biological characterization of a new photolabile precursor of D-aspartic acid, alpha-carboxynitrobenzyl-caged D-aspartate (alpha-CNB-caged D-aspartate), and its application for studying the molecular mechanism of the neuronal excitatory amino acid carrier 1 (EAAC1). Investigation of the photochemical properties of alpha-CNB-caged D-aspartate by transient absorption spectroscopy of the aci-nitro intermediate revealed that it photolyzes with a quantum yield of 0. 19 at pH 7.0. The major component of the aci-nitro intermediate (77% of the total absorbance) decays with a time constant of 26 s. This decay is slowed by only a factor of 2 when increasing the pH to 10. A minor component (21%) decays with a time constant of 410 s and is pH insensitive. The compound was tested with respect to its biological activity with the glutamate transporter EAAC1 expressed in HEK293 cells. Whole-cell current recordings from these cells in the presence and absence of alpha-CNB-caged D-aspartate demonstrated that the compound neither activates nor inhibits EAAC1. Upon photolysis, D-aspartate-mediated whole-cell currents were generated. In contrast to laser-pulse photolysis experiments with alpha-CNB-caged L-glutamate, only a minor and much slower transient current component was observed. These results indicate that the substrate translocation step, which is not rate-limiting for the overall turnover of the transporter with L-glutamate, becomes rate-limiting when D-aspartate is translocated. The results demonstrate that the new caged D-aspartate derivative is a useful tool for the investigation of the molecular mechanism of glutamate transporters and probably other aspartate translocating systems using rapid chemical kinetic techniques.

Amino Acid Transport System X-AG↗
PubMed1981

Is aspartic acid the neurotransmitter of the perforant pathway?

In order to determine whether an amino acid may act as a neurotransmitter in the perforant pathway we examined the effect of lesion of rat entorhinal cortex on the concentrations of various amino acids in the hippocampus proper and fascia dentata. Only the aspartic acid content was found significantly decreased after the lesion. This decreases is not due to a loss from target cells of the perforant pathway, but rather to a loss from its degenerating terminals.

Amino Acids↗
PubMed1997

Bond-specific chemical cleavages of peptides and proteins with perfluoric acid vapors: novel peptide bond cleavages of glycyl-threonine, the amino side of serine residues and the carboxyl side of aspartic acid residues.

Peptide bond cleavages by vapors composed of various from aqueous solutions of perfluoric acid were studied using synthetic peptides and proteins, and specific conditions were established for peptide bond cleavages including a novel cleavage of the glycyl-threonine bond. The peptide bonds on the aminosides of serine residues were cleaved by exposure to a vapor of 75% aqueous heptafluorobutyric acid at 30 or 50 degrees C for 24 h. Glycyl-threonine peptide bonds were cleaved with vapors of various concentrations (5, 75, and 90%) of heptafluorobutyric acid at 30-40 degrees C for 24 h. The peptide bonds on the carboxylsides of aspartic acid residues were cleaved by exposure to a vapor of 0.2% heptafluorobutyric acid at 90 degrees C for 4 to 24 h. The same vapor cleaved aspartyl-proline bonds under milder conditions such as at 60 degrees C for 16 h, under which the other aspartyl bonds were uncleaved. These specific chemical cleavages were applied to several proteins including newly characterized proteins.

Amino Acid Sequence↗
PubMed1991

Transport of arginine and aspartic Acid into isolated barley mesophyll vacuoles.

The transport of arginine into isolated barley (Hordeum vulgare L.) mesophyll vacuoles was investigated. In the absence of ATP, arginine uptake was saturable with a K(m) of 0.3 to 0.4 millimolar. Positively charged amino acids inhibited arginine uptake, lysine being most potent with a K(i) of 1.2 millimolar. In the presence of free ATP, but not of its Mg-complex, uptake of arginine was drastically enhanced and a linear function of its concentration up to 16 millimolar. The nonhydrolyzable adenylyl imidodiphosphate, but no other nucleotide tested, could substitute for ATP. Therefore, it is suggested that this process does not require energy and does not involve the tonoplast ATPase. The ATP-dependent arginine uptake was strongly inhibited by p-chloromercuriphenylsulfonic acid. Furthermore, hydrophobic amino acids were inhibitory (I(50) phenylalanine 1 millimolar). Similar characteristics were observed for the uptake of aspartic acid. However, rates of ATP-stimulated aspartic acid transport were 10-fold lower as compared to arginine transport. Uptake of aspartate in the absence of ATP was negligible.

Journal Article↗
PubMed1999

Critical requirement for aspartic acid at position 82 of myelin basic protein 73-86 for recruitment of V beta 8.2+ T cells and encephalitogenicity in the Lewis rat.

We synthesized single amino acid-substituted peptide analogues of guinea pig myelin basic protein (MBP) 73-86 to study the importance of aspartic acid at residue 82 (QKSQRSQDENPV), which previous reports have suggested is a critical TCR contact residue. Whereas the wild-type 73-86 peptide elicited severe experimental autoimmune encephalomyelitis (EAE) in the Lewis rat, none of the peptide analogues with substitutions at position 82 were capable of inducing EAE. The inability to cause EAE was not due to a failure to bind MHC or to elicit T cell proliferation and cytokine secretion. T cells specific for MBP73-86 did not cross-react with any of the analogues tested, further indicating the importance of this residue in T cell responses to 73-86. Analysis by flow cytometry showed that only the wild-type 73-86 peptide was capable of recruiting V beta 8.2+ T cells, which have been shown previously to be important for disease induction. Reduced expression of the V beta 8.2 TCR was also seen in Lewis rats protected from EAE by coimmunization of MBP73-86 with 73-86(82D-->A), despite an increase in cytokine production when both peptides were present during in vitro culture. The data indicate that aspartic acid 82 is a critical TCR contact residue and is required for the recruitment of V beta 8.2+ T cells and the encephalitogenic activity of MBP73-86.

Amino Acid Sequence↗
PubMed2006

Poly (ethylenimine)-grafted-poly [(aspartic acid)-co-lysine], a potential non-viral vector for DNA delivery.

A potential non-viral gene-transfer vector, poly(ethylenimine)-grafted-poly[(aspartic acid)-co-lysine] (PSL), has been developed by thermal polycondensation of aspartic acid and lysine under reduced pressure. Low-molecular-mass branch poly(ethylenimine) (PEI600) was conjugated to the backbone. The chemical structure of the resulting co-polymer was identified by 1H-NMR, FT-IR, TGA and X-ray diffraction. The results of the MTT assay showed that at concentration up to 4000 nmol/l of the vector cell viability was over 80% and showed low toxicity. Electrophoretic retardation and ethidum bromide assay showed that at N/P ratios 12-15 (w/w) the DNA could be condensed and neutralized. Using the zeta potential assay we discovered that it had a high positive charge on its surface of the particle (over 30 mV). The particle sizes of the co-polymer/DNA complexes were 150-170 nm, as measured by DLS and AFM. Compared with PEI600, co-polymer/DNA complexes showed a significant enhancement of transfection activity in the absence and presence of serum in NT2 and COS7 cell lines. This means that the PEI600-PSL co-polymer is a promising candidate for gene delivery.

Animals↗