Aspartate Ion Research Articles

Understanding the Steric Structures of Dicarboxylate Ions Incorporated in Octacalcium Phosphate Crystals.

Octacalcium phosphate (OCP) can incorporate various dicarboxylate ions in the interlayer spaces of its layered structure. Although not proven, these incorporated ions are believed to have a linear structure. In this study, the steric structures of twelve different dicarboxylate ions incorporated into OCP were investigated by comparing the experimentally determined interlayer distance of the OCP with the distance estimated using the molecular sizes of dicarboxylic acids calculated by considering their steric structures. The results revealed that the incorporated succinate, glutarate, adipate, pimelate, suberate, and aspartate ions possessed linear structures, whereas the incorporated azelate, sebacate, methylsuccinate, and malate ions exhibited bent structures. Further, the incorporated mercaptosuccinate ions featured linear, bent, other types of structures. Moreover, the steric structure of the incorporated malonate ion significantly differed from those of other dicarboxylate ions. The computational approach employed in this study is expected to deepen our understanding of the steric structures of dicarboxylate ions incorporated in the OCP interlayer spaces.

Isotope-labeled aspartate sidechain as a non-perturbing infrared probe: Application to investigate the dynamics of a carboxylate buried inside a protein

Because of their negatively charged carboxylates, aspartate and glutamate are frequently found at the active or binding site of proteins. However, studying a specific carboxylate in proteins that contain multiple aspartates and/or glutamates via infrared spectroscopy is difficult due to spectral overlap. We show, herein, that isotopic-labeling of the aspartate sidechain can overcome this limitation as the resultant 13COO− asymmetric stretching vibration resides in a transparent region of the protein IR spectrum. Applicability of this site-specific vibrational probe is demonstrated by using it to assess the dynamics of an aspartate ion buried inside a small protein via two-dimensional infrared spectroscopy.

Conformational analysis of alkali metal complexes of aspartate dianion and their interactions in gas phase

The gas-phase geometry optimizations of mono and dinuclear complexes of dianionic species of aspartic acid, asp 2− with lithium, sodium and potassium cations were carried out using density functional calculation at the B3LYP/6-311++G(d,p) level. The metal ion affinities (MIAs) of asp 2− species and its complexes [asp-M] −, M = Li +, Na + and K + were determined using the vibrational frequency calculations at the same level of theory. The most stable complex conformer for aspartate complexes with Li +, Na + and K + alkali cations were found as a tri-coordinated form. All complexations of [asp-M] − and [asp-M 2] complexes were found to be exothermic reactions. Relative bond distances between the alkali metal cation M + and the binding atoms of aspartate ion in [asp-M] − and [asp-M 2] complexes are in decreasing order: K + > Na + > Li +.

The effect of aspartic acid on the binding of transition metals to kaolinite

The effect of aspartic acid on the adsorption of Pb(II), Cu(II), Zn(II), Co(II), and Mn(II) on kaolinite at 25 °C in the presence of 5 mM KNO 3 was investigated by means of potentiometric titrations and adsorption measurements over a range of pH and concentration. Data were modeled by extended constant capacitance models. Aspartic acid slightly enhanced the adsorption of Pb(II), Zn(II), and Co(II) at low pH, but inhibited the adsorption of all the metal ions at higher pH. Adsorption of Cu(II) and Co(II) was inhibited strongly. Because aspartic acid is adsorbed only weakly by kaolinite, inhibition of metal ion adsorption depends on the ability of aspartic acid to form complexes with the various metal ions together with the adsorption characteristics of these complexes. In particular suppression of adsorption at high pH arises from competition between surface sites and dissolved aspartate ions for the available metal ions. Cu(II) and Co(II) form complexes with aspartic acid more strongly than the other metals. As these complexes do not adsorb, Cu(II) and Co(II) suffer greater suppression from aspartic acid than the other metals. There was no evidence of adsorption of aspartic acid complexes to the permanently charged kaolinite faces.

Ramachandran backbone potential energy surfaces of aspartic acid and aspartate residues: implications on allosteric sites in receptor–ligand complexations

Ramachandran backbone potential energy surfaces (PES) were generated for N-acetyl- l-aspartic acid- N′-methylamide and N-acetyl- l-aspartate- N′-methylamide. Relatively few minima were observed from the Ramachandran PES of the aspartate ion while many existed for both endo and exo forms of the aspartic acid residue. By comparing the relative stabilization energies as well as the vertical and adiabetic proton affinities of the two forms the aspartic acid residue, it was previously determined that aspartic acid may rather change its backbone conformation before deprotonation into the aspartate ion. Taken together, many stable conformers may exist for both endo and exo forms of aspartic acid but when deprotonated they lead to the same aspartate ion which has remarkably few conformations. This feature may have significant biological implications, and a receptor–ligand complexation model is proposed where aspartate and aspartic acid could represent, respectively, resting and active states of a putative binding site in a hypothetical protein. More importantly, however, the aspartyl residues may represent important allosteric sites for regulatory ions, directly modulating the specificity of ligand docking in a receptor protein and affecting downstream biological mechanisms.

Characterization of stretch-activated ion currents in isolated atrial myocytes from human hearts.

To explore further the mechanisms that may underlie cardiac arrhythmia, we analysed stretch-activated ion currents in human atrial myocytes. Longitudinal stretch of freshly isolated atrial myocytes prolonged the duration of action potentials, depolarized the resting membrane potential and caused extra action potentials. Under voltage-clamp conditions, the amplitude of stretch-induced transmembrane currents increased reversibly with the intensity of stretch. Stretch-activated currents ( I(SAC)) had a reversal potential of 0 mV and were insensitive to substitution of Cl(-) with aspartate ions in the extracellular fluid. I(SAC) was suppressed by 5 micro M gadolinium (Gd(3+)). Furthermore, mechanical stretch decreased transmembrane ion fluxes through L-type calcium channels (I(Ca,L)). This reduction of I(Ca,L) was inhibited by dialysing the cells for 5 min with 5 mM BAPTA prior to application of stretch. In contrast, both BAPTA and removal of Ca(2+) from the extracellular bathing solution had no significant effect on stretch activation of I(SAC). These findings suggest that non-selective cation channels in human atrial myocytes are sensitive to mechanical stimulation. We propose that activation of transmembrane influx of cations, preferentially Na(+), by local stretch may play a role in cardiac arrhythmia.

Two Related Rolling Circle Replication Plasmids from Salt-Tolerant Bacteria

In a range of salt-tolerant bacteria isolated from soil, rhizosphere, and phyloplane, cross-hybridization tests revealed a group of seven plasmids which were chosen for further study. Two plasmids (pSH1418 and pSH1451) were picked as representative examples of the two related subgroups. Restriction mapping and Southern blotting identified a region common to the two plasmids which later was identified as encoding the replication functions. We were unable to join these plasmids to high-copy-number vectors but this was possible with low-copy-number IncP vectors. InEscherichia coli,cloned plasmids pSH1418 and pSH1451 conferred salt tolerance but the phenotype was unstable, with the loss of salt tolerance apparently being correlated with structural instability of the plasmid DNA. Plasmid pSH1451 was sequenced and shown to be closely related to RCR plasmids of Gram-positive bacteria. The host of this plasmid was classified asBacillus pumilusby rDNA typing and lipid profiling by gas chromatography. A number of open reading frames (orfs) which could code for salt tolerance or other functions were identified in the plasmid sequence. Sequence similarity to previously sequenced genes suggested that the products of orf4 and orf5 may work together to transport a molecule such as aspartate ion that may promote osmotolerance.

X‐ray studies on crystalline complexes involving amino acids and peptides

L-Lysine D-glutamate crystallizes in the monoclinic space group P2(1) with a = 4.902, b = 30.719, c = 9.679 A, beta = 90 degrees and Z = 4. The crystals of L-lysine D-aspartate monohydrate belong to the orthorhombic space group P2(1)2(1)2(1) with a = 5.458, b = 7.152, c = 36.022 A and Z = 4. The structures were solved by the direct methods and refined to R values of 0.125 and 0.040 respectively for 1412 and 1503 observed reflections. The glutamate complex is highly pseudosymmetric. The lysine molecules in it assume a conformation with the side chain staggered between the alpha-amino and the alpha-carboxylate groups. The interactions of the side chain amino groups of lysine in the two complexes are such that they form infinite sequences containing alternating amino and carboxylate groups. The molecular aggregation in the glutamate complex is very similar to that observed in L-arginine D-aspartate and L-arginine D-glutamate trihydrate, with the formation of double layers consisting of both types of molecules. In contrast to the situation in the other three LD complexes, the unlike molecules in L-lysine D-aspartate monohydrate aggregate into alternating layers as in the case of most LL complexes. The arrangement of molecules in the lysine layer is nearly the same as in L-lysine L-aspartate, with head-to-tail sequences as the central feature. The arrangement of aspartate ions in the layers containing them is, however, somewhat unusual. Thus the comparison between the LL and the LD complexes analyzed so far indicates that the reversal of chirality of one of the components in a complex leads to profound changes in molecular aggregation, but these changes could be of more than one type.

Lysinium, argininum, glutamate, and aspartate ions in water solution

AbstractSCF‐LCAO‐MO ab initio calculations were carried out for the interaction between a charged amino acid and a water molecule. The results obtained were fitted by an analytical potential function of the atom–atom type, and the corresponding potential surfaces were examined by means of orientationally optimized isoenergy contour maps. Monte Carlo simulations were also carried out on a few selected solute–water clusters at T = 300 K, in order to obtain insight into the solvation structure.

ChemInform Abstract: STRUCTURAL, SPECTROSCOPIC, AND MAGNETIC PROPERTIES OF DIAQUA(L‐ASPARTATO)NICKEL(II) HYDRATE

The crystal structure of the title compound was determined by X-ray analysis. The compound crystallizes in the orthorhombic space group P212121 with cell dimensions a= 12.306(2), b= 8.996(2), c= 7.596(1)A, and Z= 4. The structure was solved by the heavy-atom method and refined by least-squares calculations to a final R value of 0.034. The compound is isostructural with the corresponding zinc(II) salt. The structure consists of polymeric linear chains in which the Ni atom is co-ordinated in a distorted octahedral manner by one aspartate ion, acting as a tridentate ligand, by two water molecules, and by one β-carboxylate O atom of a second aspartate ion. Magnetic and spectroscopic results are also discussed.

Molecular orbital analysis of the catalytic process of serine proteinases: Effect of environment on protonation of the histidine-aspartate diad of subtilisin

The catalytic triad of serine proteinases is composed of serine, histidine and aspartate residues. During catalysis the imidazole group of histidine, as a general base, accepts the proton from the hydroxyl group of serine. In this work the equilibrium states of the proton between the protonated imidazole group and the aspartate ion, as well as the factors determining this equilibrium, are examined by various quantum chemical approximations. The protonated histidine—aspartate diad of subtilisin BPN′has been modelled by the imidazole—formic acid system. It is found that the CNDO/2 and ab initio STO-3G basis set calculations overestimate the stability of the neutral form where the proton is attached to the aspartate side chain. A more probable proton transfer energy is obtained if the total energy of the diad is partitioned into bond and interaction energy terms calculated with 4-31G and STO-3G basis sets, respectively. However, even this approximation is insufficiently accurate to establish unambiguously the position of the proton in the gas phase. Nevertheless, the effects of the enviromnent on proton transfer could be estimated with more certainty. It is found that each component of the environment, i.e. (1) aminoacid residues of subtilisin within 1 nm of the diad, (2) three water molecules and (3) a counter ion, stabilizes the imidazolium—spartate ion pair of the diad so that the proton cannot be transferred from the imidazolium to the aspartate ion. These results clearly demostrate the crucial role of the environment in the reactivities of the catalytic group of enzymes.

Molybdenum(VI) complexation by amino-acids. Part 1 Species in aqueous solution of sodium molybdate and L-aspartate

The complexation of molybdenum(VI) by L-aspartate in dilute aqueous solutions, at pH 6, was studied using u.v. spectrophotometry,1H and13C n.m.r. spectroscopy. A single complex anion, [MoO3(C4H5NO4)]2−, is observed in solution. The conformation of the aspartate ion in the complex was determined and shown to be consistent with it acting as a terdentate ligand. The formation constant of the complex was determined at different ionic strengths. Job's method has been employed, here and elsewhere, to study the stoichiometry of the complex. However, the result is strongly affected by polymerization of molybdenum(VI): this effect is discussed.

L-Arginine L-aspartate

C 6 H 15 N 4 O 2 + .C 4 H 6 NO 4 - , monoclinic, P2,,a = 5.511 (3), b = 8.438 (4), c = 15.265 (9) A , β = 97.9 (I) ° , D m = 1.467 (8) (flotation), D c = 1.452 Mg m -3 , Z = 2. The structure has been refined to a final R value of 0.044 for 1226 independent counter-measured reflections. The conformation of the arginine molecule is different from those previously observed, whereas the conformation of the aspartate ion is similar to that found in L-aspartic acid, DL-aspartic acid and L-lysine L-aspartate. The unlike molecules aggregate into separate alternating layers and the a-amino and acarboxylate groups in the arginine layer are periodically brought into close proximity in a 'headto-tail' arrangement. There exist a specific ion-pair interaction involving electrostatic attraction and two nearly parallel N-H...O hydrogen bonds between the guanidyl group and the a-carboxylate group of the aspartate ion.

Molecular orbital analysis of the catalytic process of serine proteinases: Effect of environment on protonation of the histidine aspartate diad of subtilisin

The catalytic triad of serine proteinases is composed of serine, histidine and aspartate residues. During catalysis the imidazole group of histidine, as a general base, accepts the proton from the hydroxyl group of serine. In this work the equilibrium states of the proton between the protonated imidazole group and the aspartate ion, as well as the factors determining this equilibrium, are examined by various quantum chemical approximations. The protonated histidine-aspartate diad of subtilisin BPN' has been modelled by the imidazole-formic acid system. It is found that the CNDO/2 and ab initio STO-3G basis set calculations overestimate the stability of the neutral form where the proton is attached to the aspartate side chain. A more probable proton transfer energy is obtained if the total energy of the diad is partitioned into bond and interaction energy terms calculated with 4-31G and STO-3G basis sets, respectively. However, even this approximation is insufficiently accurate to establish unambiguously the position of the proton in the gas phase. Nevertheless, the effects cf the environment on proton transfer could be estimated with more certainty. It is found that each component of the environment, i.e. (1) amino-acid residues of subtilisin within 1 nm of the diad, (2) three water molecules and (3) a counter ion, stabilizes the imidazolium- aspartate ion pair of the diad so that the proton cannot be transferred from the imidazolium to the aspartate ion. These results clearly demostrate the crucial role of the environment in the reactivities of the catalytic group of enzymes.

Structural, spectroscopic, and magnetic properties of diaqua(L-aspartato)nickel(II) hydrate

The crystal structure of the title compound was determined by X-ray analysis. The compound crystallizes in the orthorhombic space group P212121 with cell dimensions a= 12.306(2), b= 8.996(2), c= 7.596(1)Å, and Z= 4. The structure was solved by the heavy-atom method and refined by least-squares calculations to a final R value of 0.034. The compound is isostructural with the corresponding zinc(II) salt. The structure consists of polymeric linear chains in which the Ni atom is co-ordinated in a distorted octahedral manner by one aspartate ion, acting as a tridentate ligand, by two water molecules, and by one β-carboxylate O atom of a second aspartate ion. Magnetic and spectroscopic results are also discussed.

Preparation and Isomerization of Isomers of the l- or d-Aspartato(l-histidinato)cobalt(III) Complex

Abstract The six isomers of the [Co(l- or d-asp)(l-his)] complex (asp=aspartate ion and his=histidinate ion) have been prepared and the isomerization studied in the absence of any catalyst. The equilibrium mole fractions of these isomers in water has been found for l-transO5cisN5, l-cisO5transN5, l-fac, to be 0.53, 0.06, and 0.41, respectively, those for d-cisObcisN5, d-transO5transN5, and d-fac to be 0.48, 0.01, and 0.51 respectively. The indication is that the relative positions of the six coordinated atoms around a cobalt atom cause these unequal isomer concentration ratios. The isomerisms are dealt with by means of a network of first order reversible reactions and the absolute values of the rate constants at 80 °C have been determined.

X-ray studies on crystalline complexes involving amino acids. I. Crystal structure of L-lysine L-aspartate

Lysine aspartate, C 6 H 15 N 2 O 2 ·C 4 H 6 NO 4 , a crystalline complex or lysine and aspartic acid, crystallizes in the monoclinic space group P2 1 with two formula units in a unit cell of dimensions a = 5.539 (3), b = 7.848 (4), c = 15.324 (I5) A, β = 99.1 (I)°. The structure was solved by direct methods and Fourier techniques and refined to an R value of 0.069 for 1134 photographically observed reflexions. The dimensions and the conformation of the lysine molecule are similar to those observed in lysine mono-hydrochloride dihydrate. The side-chain carboxyl group of the aspartate ion is deprotonated unlike that in L- and DL-aspartic acid. The bond lengths and angles in the aspartate ion, except those in the side-chain carboxylate group, are comparable with those in L- and DL-aspartic acid. Considerable differences, however, exist in the conformation of the molecule in these structures. The crystal structure of lysine aspartate consists of alternating layers, one layer comprising lysine molecules and the other, aspartate ions. The two layers are interconnected primarily by hydrogen bonds between the side-chain amino group of lysine and carboxylate oxygen atoms belonging to neighbouring aspartate ions.

ChemInform Abstract: STEREOISOMERS OF THE BIS(L‐HYDROGENASPARTATO)‐TRIMETHYLENEDIAMINECOBALT(III) COMPLEX

AbstractDie Reaktion von trans‐Dichloro‐bis‐[trimethylendiamiii]‐kobalt(III) mit L‐Aspartinsäure liefert8 Stereoisomere des Titelkornplexes, die durch Ionenaustausch‐ Chromatographie getrennt werden.

Stereoisomers of the Bis(l-hydrogenaspartato)trimethylenediaminecobalt(III) Complex

Abstract The bis(l-hydrogenaspartato)trimethylenediaminecobalt(III) complex has been prepared by the reaction of the trans-[CoCl2(tn)2]+ complex with l-aspartic acid, and its eight stereoisomers have been separated by an ion-exchange chromatographic method. The six isomers are trans(O)-Λ and -Δ, cis(O)cis(N)-Λ and -Δ and trans(N)-Λ and -Δ isomers, in which either aspartate ion forms the five-membered chelate ring through an N atom of the amino group and an O atom of the α-carboxylate group. The remaining isomers are Λ- and Δ-trans(O) ones containing a five-membered chelate ring and a six-membered ring of l-aspartate ions. On the other hand, stereoselective formations have been found in the Λ,Δ, and Λ isomers for the trans(O), cis(O)cis(N), and trans(N) isomers respectively. It has become apparent that these stereoselectivities agree with those found for the corresponding l-pn and en complexes, while the orders of the formation amounts for the three geometrical isomers disagree.

Light-induced changes in photoreceptor membrane resistance and potential in Gecko retinas. I. Preparations treated to reduce lateral interactions.

The time-course of the light-induced changes in membrane voltage and resistance were measured for single photoreceptors in the retina of Gekko gekko. In the surgically isolated retina, small stimuli directed toward the impaled receptor produced a membrane hyperpolarization the time-course of which was identical to that of the increase in membrane resistance. In the eyecup preparation nearly identical time-courses were evoked only after perfusion of the vitreous surface with solution having high (Mg(++)). Disparate time-courses were obtained in (a) the isolated retina when large or displaced stimuli were used, and (b) the eyecup preparation when it was treated normally (see Pinto and Pak. 1974. J. Gen. Physiol. 64:49) and when it was exposed to aspartate ions or hypoxia. These results are consistent with the hypothesis that the receptor potential (elicited in the impaled receptor as a result of quanta only it captures) is generated by a single ionic process that decreases membrane conductance. These measurements provide a means to distinguish the receptor potential from interactions. From direct measurements of membrane time constant and total resistance in darkness, total membrane capacitance was calculated. The mean capacitance was 7.1 x 10(-5) microF. This high value is consistent with anatomical observations of membrane infoldings at the base of gecko photoreceptors.