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At least 37 records · Page 2Linked to original sources
PubMed2005

Electrochemical behavior of a covalently modified glassy carbon electrode with aspartic acid and its use for voltammetric differentiation of dopamine and ascorbic acid.

Aspartic acid was covalently grafted on to a glassy carbon electrode (GCE) by amine cation radical formation in the electrooxidation of the amino-containing compound. X-ray photoelectron spectroscopic (XPS) measurement and cyclic voltammetric experiments proved the aspartic acid was immobilized as a monolayer on the GCE. Electron transfer to Fe(CN)6(4-) in solution of different pH was studied by cyclic voltammetry. Changes in solution pH resulted in the variation of the charge state of the terminal group; surface pK(a) values were estimated on the basis of these results. Because of electrostatic interactions between the negatively charged groups on the electrode surface and dopamine (DA) and ascorbic acid (AA), the modified electrode was used for electrochemical differentiation between DA and AA. The peak current for DA at the modified electrode was greatly enhanced and that for AA was significantly reduced, which enabled determination of DA in the presence of AA. The differential pulse voltammetric (DPV) peak current was linearly dependent on DA concentration over the range 1.8 x 10(-6)-4.6 x 10(-4) mol L(-1) with slope (nA micromol(-1) L) and intercept (nA) of 47.6 and 49.2, respectively. The detection limit (3delta) was 1.2 x 10(-6) mol L(-1). The high selectivity and sensitivity for dopamine was attributed to charge discrimination and analyte accumulation. The modified electrode has been used for determination of DA in samples, in the presence of AA, with satisfactory results.

Ascorbic Acid↗
PubMed1979

Rapid method for the assay of 4-aminobutyric acid (GABA), glutamic acid and aspartic acid in brain tissue and subcellular fractions.

The thin-layer electrophoretic separation at pH 4.8 of brain extracts and a procedure for fluorescent staining of the plates with fluorescamine are described for the rapid routine determination of 4-aminobutyric acid (GABA), glutamic acid and aspartic acid in brain extracts and in particulate fractions of brain tissue. Automated sample application, electrophoretic separation using two chambers, and quantitation by in situ fluorescence scanning allows the assay of 280 samples within three working days. The method is reproducible (S.D. less than 8% of the mean) within the range of 0.2--2 nmole per spot. The staining procedure can be applied to a variety of related analytical problems. The method has proved useful for the determination of the specific radioactivities of GABA, glutamic acid and aspartic acid in metabolic studies.

Aging↗
PubMed2002

Non-peptide alpha(v)beta(3) antagonists. Part 3: identification of potent RGD mimetics incorporating novel beta-amino acids as aspartic acid replacements.

Potent non-peptidic alpha(v)beta(3) antagonists have been prepared incorporating various beta-amino acids as aspartic acid mimetics. Modification of the beta-alanine 3-substituents alters the potency and physicochemical properties of these receptor antagonists and in some cases provides orally bioavailable alpha(v)beta(3) inhibitors.

Amino Acids↗
PubMed1999

A novel glutamic acid to aspartic acid mutation near the end of the 2B rod domain in the keratin 1 chain in epidermolytic hyperkeratosis.

We report a mutation in a mild case of epidermolytic hyperkeratosis that results in a glutamic acid to aspartic acid substitution in a novel location, codon 477 or position 106 of the 2B rod domain of the keratin 1 chain. This residue has been conserved in all intermediate filament chains and lies near the beginning of the highly conserved helix termination sequence and just prior to the predicted molecular overlap region. Keratin filaments assembled in vitro from chains bearing this substitution are abnormal, indicating that the glutamic acid residue is critically involved in ionic interactions in intermediate levels of filament structure.

Amino Acid Substitution↗
PubMed1992

Estimation of age from a tooth by means of racemization of an amino acid, especially aspartic acid--comparison of enamel and dentin.

In a study of age estimation from teeth by means of measuring racemization of aspartic acid (Asp), a representative amino acid, the accuracy of data from enamel and dentin in the same tooth was compared. The correlation of D/L ratio of aspartic acid with actual age gave the following parameters: r = 0.928, sigma = +/- 5.2, k = 4.47 x 10(-4) yr-1 in enamel and r = 0.995, sigma = +/- 1.4, k = 5.75 x 10(-4) yr-1. The difference in ages between one estimated by the D/L ratio and the actual one was within +/- 3 years in dentin, while in enamel an error of from 2 to 11 years was observed. Reaction rate constants of the racemization in a dry postmortem state (15 degrees C) were calculated as k = 9.70 x 10(-8) yr-1 in enamel, and k = 1.33 x 10(-7) yr-1 in dentin. Compared to rates determined from teeth recently extracted from living subjects, the rate was higher in dentin than in enamel. These data reconfirmed that dentin is superior to enamel in making exact age estimations from teeth.

Adult↗
PubMed2003

Aggregation behaviors and their pH sensitivity of cholesterol-conjugated proteinoids composed of glutamic acid and aspartic acid matrix.

Cholesterol-conjugated proteinoids and their aggregation behaviors were investigated with model proteinoid systems. Model proteinoids of molecular weights in the range of 4000 to 6000 were synthesized by anhydrous thermal condensation forming a matrix with glutamic acid and aspartic acid and of naturally occurring amino acids. Nuclear magnetic resonance and Fourier transform infrared spectra suggested that cholesterol was conjugated to carboxyl group-forming pendants. Native water-soluble proteinoids can form microspheres in acidified or heated conditions, but the cholesterol-conjugated proteinoids were found to form aggregates in water, regardless of the temperature or pH of the solutions. The hydrophobic pendant moieties come to a compact association in core, whereas the hydrophilic chains provide a shield layer.

Aspartic Acid↗
PubMedDate not supplied

Helix-coil stability constants for the naturally occurring amino acids in water. 16. Aspartic acid parameters from random poly(hydroxybutylglutamine-co-L-aspartic acid).

The synthesis and characterization of water-soluble random copolymers containing L-aspartic acid with N5-(4-hydroxybutyl)-l-glutamine, and the thermally induced helix-coil transitions of these copolymers in water and in 0.1 N KCl, are described. The incorporation of L-aspartic acid was found to decrease the helix content of the polymer at both high and low pH, in water and also in 0.1 N KCl. The Zimm-Bragg parameters sigma and s for the helix-coil transition in poly(L-aspartic acid) in water and in 0.1 N KCl were deduced from an analysis of the melting curves of the copolymers in the manner described in earlier papers. Corrections were made for the presence of a small amount of racemized aspartic acid, using data from random copolymers containing D-aspartic acid as the guest residue. The computed values of s indicate that L-aspartic acid destabilizes helical sequences at all temperatures in the range of 0-70 degrees C. Titrations of the copolymers and of N-acetyl-N'-methyl-L-aspartic acid amide in 0.1 N KCl are described.

Aspartic Acid↗
PubMed1984

Effects of glutamic acid, kainic acid and aspartic acid on GABA release from rat retina degenerated by kainic acid.

The effects of L-glutamic acid (Glu), kainic acid (KA) and L-aspartic acid (Asp) on 14C-GABA release from the rat retina degenerated by KA were investigated. In the normal rat retina, Glu initially enhanced GABA release and subsequently inhibited it. Both KA and Asp did not have dual effects; KA enhanced GABA release, while Asp inhibited it. In the KA-degenerated retina, the stimulatory effect of Glu or KA on GABA release was markedly suppressed, while the inhibitory effects of Glu or Asp were preserved.

Animals↗
PubMed2004

Enzymatic hydrolysis of alpha- and beta-oligo(L-aspartic acid)s by poly(aspartic acid) hydrolases-1 and 2 from Sphingomonas sp. KT-1.

The enzymatic hydrolysis of alpha- and beta-oligo(L-aspartic acid)s by PAA hydrolase-1 and PAA hydrolase-2 (purified from Sphingomonas sp. KT-1) was performed to elucidate the mechanism of the microbial degradation by Sphingomonas sp. KT-1 of the thermally synthesized alpha,beta-poly(D,L-aspartic acid) (tPAA). GPC analysis of the hydrolyzed products of alpha- and beta-tetra(L-aspartic acid)s by PAA hydrolase-1 has showed that PAA hydrolase-1 is capable of hydrolyzing only the specific amide bonds between beta-aspartic acid units. The RP-HPLC analysis of the enzymatic hydrolysis of beta-oligo(L-aspartic acid)s (4 and 5 mers) by PAA hydrolase-1 has suggested that the enzymatic hydrolysis of beta-oligo(L-aspartic acid)s occurs via an endo-mode cleavage. In contrast, PAA hydrolase-2 hydrolyzed both alpha- and beta-oligo(L-aspartic acid)s via an exo-mode cleavage to yield L-aspartic acid as a final product. A kinetic study on the enzymatic hydrolysis of alpha-oligo(L-aspartic acid)s (3 to 7 mers) by PAA hydrolase-2 has indicated that Km values are almost independent of the number of monomer units in oligomers of 4 to 7 mers, while that Vmax values are markedly dependent on the chain length and show a maximum value at 5 mer.

Aspartic Acid↗
PubMed2000

Analysis of the enzymatic racemization of D-aspartic acid to L-aspartic acid by the on-line coupling of a solid-phase extraction column and a ligand-exchange high-performance liquid chromatography column.

D-Aspartic acid can be enzymatically biotransformed with D-amino acid oxidase and aminotransferase to L-aspartic acid. The reaction was surveyed at three temperatures and a period of 3 days, however, L-aspartic acid can be produced only at the reaction temperature 90 degrees C. However, the separation of D-aspartic acid and L-aspartic acid by ligand-exchange chromatography showed matrix interference. Therefore, the column-switching technique by coupling a solid-phase extraction (SPE) column to the analytical ligand-exchange HPLC column was used to eliminate the matrix effect. The pretreatment of reaction samples with the SPE column was considered as a combination of size-exclusion chromatography and ion-pair chromatography. The ion-pair reagent was 0.005 M sodium 1-octanesulfonate aqueous solution adjusted to pH 2.2. Part of the first eluted peak from the SPE column was then switched through the ligand-exchange column and analyzed with a 0.25 mM Cu2+ aqueous mobile phase of pH 3.6. The quantitative analysis of D- and L-aspartic acids was performed by the standard addition method. Overall, the separation and analysis of D- and L-aspartic acids in the enzymic solution was convenient, fast, and successful with the developed on-line LC-LC column-coupling and column-switching system.

Aspartic Acid↗
PubMed2006

Partial poly(glutamic acid) <--> poly(aspartic acid) exchange in layer-by-layer polyelectrolyte films. Structural alterations in the three-component architectures.

Layer-by-layer (LBL) polyelectrolyte films were constructed from poly(L-glutamic acid) (PGA) and poly(L-aspartic acid) (PAA) as polyanions, and from poly(L-lysine) (PLL) as the polycation. The terminating layer of the films was always PLL. According to attenuated total reflection Fourier transform infrared measurements, the PGA/PLL and PAA/PLL films, despite their chemical similarity, had largely different secondary structures. Extended beta-sheets dominated the PGA/PLL films, while alpha-helices and intramolecular beta-sheets dominated the PAA/PLL films. The secondary structure of the polyelectrolyte film affected the adsorption of human serum albumin (HSA) as well. HSA preserved its native secondary structure on the PGA/PLL film, but it became largely deformed on PAA/PLL films. Both PGA and PAA were able to extrude to a certain extent the other polyanion from the films, but the structural consequences were different. Adding PAA to a (PGA/PLL)5-PGA film resulted in a simple exchange and incorporation: PGA/PLL and PAA/PLL complexes coexisted with their unaltered secondary structures in the mixed film. The incorporation of PGA into a (PAA/PLL)5-PAA film was up to 50% and caused additional beta-structure increase in the secondary structure of the film. The proportions of the two polyanions were roughly the same on the surfaces and in the interiors of the films, indicating practically free diffusion for both polyanions. The abundance of PAA/PLL and PGA/PLL domains on the film surfaces was monitored by the analysis of the amide I region of the infrared spectrum of a reporter molecule, HSA, adsorbed onto the three-component polyelectrolyte films.

Adsorption↗
PubMed1988

Studies on the role of actin's aspartic acid 3 and aspartic acid 11 using oligodeoxynucleotide-directed site-specific mutagenesis.

One or more of the five acidic amino-terminal residues of skeletal muscle actin have been implicated as being important in a number of actin-related processes. We have constructed a series of actins containing mutations at Asp3 and Asp11 and tested these mutant proteins for their ability to bind to DNase I-agarose, polymerize with rabbit skeletal muscle actin, undergo amino-terminal processing, and bind to the myosin-S1 subfragment. The mutant actins were expressed in vitro using a coupled transcription/translation system which involves the synthesis of mutant RNAs with SP6 RNA polymerase followed by their translation in a rabbit reticulocyte lysate. When Asp3 was changed to Ala, His, or Asn there was no difference in the tested properties as compared to wild type actin. These results suggest that an acidic residue at position 3 is not critical for the actin functions measured. When Asp11 was changed to Glu, Asn, or His or if the conserved Asp-Asn sequence at positions 11 and 12 was reversed, the mutants were able to copolymerize with rabbit skeletal muscle actin and be cross-linked to myosin-S1 to nearly the same extent as wild type actin. However, the amount of in vitro-synthesized actin capable of binding to DNase I-agarose with high affinity or undergoing amino-terminal processing was reduced significantly relative to the wild type actin synthesized in vitro. The Asp11 mutants ran anomalously on native polyacrylamide gels suggestive of a conformational change induced in the actin. Together, these results suggest that Asp11 may be important in proper actin folding and function.

Actins↗