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PubMed1987

Apparent identity of cerebral tyrosylsulfotransferase activities using either a cholecystokinin derivative or an acidic amino acid polymer as substrate.

The tyrosylsulfotransferase activities of rat cerebral fractions transferring [35S]sulfate groups from 3'-phosphoadenosine 5'-[35S]phosphosulfate to either Boc-cholecystokinin-8 (in non-sulfated form) or the acidic amino acid polymer (Glu, Ala, Tyr)n (6:3:1) were compared. They appear similar regarding subcellular distribution (both being enriched in the microsomal fraction) and inhibition by an excess of the acidic amino acid polymer, NaCl or 2,6-dichloro 4-nitrophenol. These results obtained with artificial substrates suggest that identical (or closely similar) tyrosylsulfotransferases are responsible for sulfation of tyrosine residues of several secretory proteins from various tissues.

Amino Acids↗
PubMed1999

Preparation and Characterization of Hybrid Organic-Inorganic Composite Materials Using the Amphoteric Property of Amino Acids: Amino Acid Intercalated Layered Double Hydroxide and Montmorillonite.

Deprotonated and protonated forms of L-tyrosine or L-phenylalanine were intercalated by Zn-Al hydrotalcite (HT) and Na-montmorillonite (Na-mont), respectively. The intercalated materials were characterized by powder X-ray diffraction, BET measurements, and FT-IR spectroscopy. Intercalation was successful as the increased basal spacings attested. For hydrotalcite this increase was always significantly larger than for montmorillonite. This fact indicated that the spatial arrangement of the amino acid moieties was very different. A model for this arrangement has been suggested. A variety of methods showed that L-Tyr(Phe)-HT was thermally less stable than HT, while the heat resistance of L-Tyr(Phe)-mont did not change.

Journal Article↗
PubMed1997

Changes in the kinetics of the acidic amino acid brain and CSF uptake during development in the rat.

Using a bilateral in situ brain perfusion technique, the rate of influx of the acidic amino acids, aspartate and glutamate, into both brain and CSF, were measured in the rat. The kinetic constants for uptake of these amino acids across the blood-brain and blood-CSF barriers in neonatal (1-week-old) and adult (7-10 weeks-old) rats were calculated; the half saturation constant (K(m)) at both barriers did not change with age, whereas the maximal transport (Vmax) at both barriers was greater in the younger age group, and reduced by more than 50% with maturity. The diffusion constant Kd at the blood-brain barrier was not different from zero at either age, although at the blood-CSF barrier there was some diffusion at both ages, which did not change with maturity. The entry of these amino acids into the neonatal brain shown in our previous study can be explained by a greater maximal transport in the neonates which, coupled with the elevated plasma amino acid concentrations of the young animal, would result in higher blood-to-brain and blood-to-CSF flux in the neonate.

Amino Acids↗
PubMed1982

Response of Schaffer collateral-CA 1 pyramidal cell synapses of the hippocampus to analogues of acidic amino acids.

Analogues of the putative excitatory transmitters aspartic acid and glutamic acid were tested for antagonism against stimulus-evoked activation of Schaffer collateral-CA 1 pyramidal cell synapses in slices of rat hippocampus. Responses to the analogues, applied via the superfusing medium, were extracellularly recorded. The compounds examined included D- and L-alpha-aminodicarboxylic acids, diaminodicarboxylic acids, phosphonate analogues of acidic amino acids, D- and L-gamma-glutamyl glycine, and the cis- and trans-isomers of piperidine 2,3-, and 2,4-dicarboxylic acid. Many of these compounds are known to be potent and selective antagonists for excitatory amino acids and a few excitatory pathways. In this hippocampal pathway most of these analogues showed relatively low and similar potency. The most potent antagonist uncontaminated with agonist activity was D-alpha-aminosuberate, with an apparent antagonist dissociation constant (Kd) of 3 mM. Only 5 of the analogues, 3 of the piperidine dicarboxylates, kainic acid, and L-alpha-aminopimelic acid, reduced the amplitude of the extracellularly recorded field potentials more than 30% at 0.5 mM. However, all of the others reduced the potential by more than 30% at 5 mM. Most analogues also evoked extracellular responses which can be attributed to depolarization of the pyramidal neurons. Agonist activity was particularly strong among the most potent analogues. These results contrast with the responses documented by others for the N-methyl-D-aspartate receptor of the dorsal-ventral root excitatory pathway of the spinal cord in which the higher homologues tested here were the most potent antagonists, and the D-isomers were more potent than the L-isomers. It also contrasts with the response of the perforant path synapses to granule cells of the dentate gyrus in which the portion derived from the lateral entorhinal cortex is sensitive to L-2-amino-4-phosphonobutyric acid. Thus the Schaffer-CA 1 pyramidal cell synaptic field utilizes a novel excitatory transmitter receptor which interacts detectably but only weakly with a variety of acidic amino acids with potent specific inhibitory action for receptors elsewhere in the central nervous system.

Amino Acids, Dicarboxylic↗
PubMed1997

Acidic amino acid accumulation by rat choroid plexus during development.

Acidic amino acid accumulation by the choroid plexuses of the lateral ventricles was investigated using 1, 2, 3 week and adult (7-10 weeks old) rats. The accumulation from both blood and CSF sides of the choroid plexuses were investigated. The uptake from blood side was studied using the bilateral in situ brain perfusion, and time-dependent uptake profiles (2, 10, 20, and 30 min) of 14C-labelled aspartate, glutamate, and NMDA were measured. [3H]Mannitol was also included in perfusion fluid as a baseline for [14C]amino acid uptake into choroidal tissue. Uptake of [14C]aspartate and [14C]glutamate declined with age, while [14C]NMDA showed no significant uptake at any age. Twenty min [3H]mannitol uptake in the 1-week-old rat was significantly greater than the adult (P < 0.05). The K(m) for [14C]aspartate and [14C]glutamate obtained from multiple time uptake profiles also showed reduction with development but it was greater than that for mannitol. [14C]Aspartate declined from 69.8 +/- 21.1 microliters.min-1.g-1 in the neonate to 40.6 +/- 4.0 microliters.min-1.g-1 in the adult (P < 0.05), while glutamate showed a sharper decline from 78.9 +/- 24.2 microliters.min-1.g-1 to 17.7 +/- 5.4 microliters.min-1.g-1 (P < 0.01). Accumulation of 14C-labelled aspartate and glutamate by the choroid plexus from CSF side was also measured using ventriculo-cisternal perfusion. The accumulation in the adult was found to be 2-3 times greater than that in the neonatal rat (P < 0.05) for both amino acids. The uptake from either side was found to be saturable, stereospecific, not inhibited by neutral amino acid analogues, and shared by both aspartate and glutamate.

Amino Acids↗
PubMed1995

Mutation at a single acidic amino acid enhances the halophilic behaviour of malate dehydrogenase from Haloarcula marismortui in physiological salts.

In a statistical analysis of the amino acid compositions of 26 halophilic proteins, 24 showed an increase in acidic amino acids and a decrease in basic ones when compared to their non-halophilic homologues. The role of acidic residues in halophilic adaptation was investigated by site-directed mutagenesis of malate dehydrogenase (MalDH) from Haloarcula marismortui. In all of 40 non-halophilic homologous proteins, the position aligned with E243 in halophilic MalDH is occupied by a non-acidic amino acid, most frequently by arginine. The E243R mutant of halophilic MalDH was constructed, over-expressed in Escherichia coli, renatured and purified. Its salt-dependent catalytic activity was not affected compared to the wild-type enzyme and both proteins have the same Km values for their substrates. The resistance to denaturation of the mutant was compared to that of the wild-type protein in different physiological salt (NaCl or KCl) and temperature conditions and interpreted in terms of classical quasi-thermodynamic parameters. The mutant is more halophilic than the wild-type protein; it is more sensitive to temperature and requires significantly higher concentrations of NaCl or KCl for equivalent stability. These results highlight the role of acidic amino acids in halophilic behaviour and are in agreement with a model in which these amino acids act cooperatively to organise hydrated ion binding to the protein.

Base Sequence↗
PubMed2003

Synthesis and anticonvulsant activity of novel bicyclic acidic amino acids.

Bicyclic acidic amino acids (+/-)-6 and (+/-)-7, which are conformationally constrained homologues of glutamic acid, were prepared via a strategy based on a 1,3-dipolar cycloaddition. The new amino acids were tested toward ionotropic and metabotropic glutamate receptor subtypes; both of them behaved as antagonists at mGluR1,5 and as agonists at mGluR2. Furthermore, whereas (+/-)-6 was inactive at all ionotropic glutamate receptors, (+/-)-7 displayed a quite potent antagonism at the NMDA receptors. In the in vivo tests on DBA/2 mice, the compounds displayed an anticonvulsant activity. The interesting pharmacological profile of (+/-)-7 qualifies it as a lead of novel neuroprotective agents.

Amino Acids, Acidic↗
PubMed1982

Putative acidic amino acid transmitters in the cerebellum. II. Electron microscopic localization of transport sites.

In structurally preserved cerebellar slices, the sites of high affinity uptake of acidic amino acids were analyzed using the nonmetabolizable analogue, D-[3H]aspartate. Electron microscopic autoradiography showed the greatest accumulation of grains to be over glial structures. The labelling of the perikarya, dendrites and axons of the putatively glutamatergic granule cells was very low. However, "hypothetical grain" analysis indicated that the terminals of these cells are probable sources of radioactivity even though they contained less than 9% of the total grains in the molecular layer. The resolution of the autoradiographic technique did not permit definitive conclusion, as the parallel fibre terminals are too small and are ensheathed by thin glial processes. Nevertheless, further supporting evidence for some D-[3H]aspartate uptake into parallel fibre terminals was obtained using mechanically chopped cerebellar slices in which compared with glia presynaptic structures are selectively preserved. It is concluded that in line with hypotheses relating to the compartmentation of glutamate metabolism, the principal sites of uptake of acidic amino acids in the cerebellum are the glial cells. The results have clear implications regarding the use of high affinity uptake as a marker for glutamatergic nerve terminals.

Animals↗
PubMed1990

Inhibition by trypsin of the high-affinity acidic amino acid transport system in C6 glioma cells.

The high-affinity uptake of the acidic amino acid D-aspartate was inhibited in a dose- and time-dependent manner, when C6 cells were exposed to trypsin. The protease decreased the maximal velocity for uptake but not its Km, consistent with a reduction in the number of competent carriers at the plasma membrane. Cellular energy production and [K+]i were unaffected, indicating that the transporter itself was the site of trypsin action. Maximum inhibition of uptake was 50%, which suggests the presence of a heterogeneous population of transporters, only half of which is sensitive to trypsin. These results support our earlier postulate that in glial cells, the high-affinity transporter for acidic amino acids is a transmembrane protein, part of which extends into the external environment.

Animals↗
PubMed1978

High-performance liquid chromatographic investigation of the amino acid, amino sugar and neutral sugar content in glycoproteins.

A methods for the simultaneous separation and determination of amino acids, amino sugars and neutral carbohydrates is described. Stepwise elution systems with sodium citrate and borate buffers have developed for the ion-exchange liquid chromatographic separation of amino acids and sugars, using 8-micrometer particle size resins and the Stein and Moore and orcinol colorimetric method for detection. With the aid of this system, the direct quantitative comparison of sugars and amino acids by liquid chromatography becomes possible for the first time.

Amino Acids↗
PubMed2003

Identification of Pseudomonas proteins coordinately induced by acidic amino acids and their amides: a two-dimensional electrophoresis study.

The acidic amino acids (Asp, Glu) and their amides (Asn, Gln) are excellent growth substrates for many pseudomonads. This paper presents proteomics data indicating that growth of Pseudomonas fluorescens ATCC 13525 and Pseudomonas putida KT2440 on these amino acids as sole source of carbon and nitrogen leads to the induction of a defined set of proteins. Using mass spectrometry and N-terminal sequencing, a number of these proteins were identified as enzymes and transporters involved in amino acid uptake and metabolism. Most of them depended on the alternative sigma factor sigma(54) for expression and were subject to strong carbon catabolite repression by glucose and citrate cycle intermediates. For a subset of the identified proteins, the observed regulatory effects were independently confirmed by RT-PCR. The authors propose that the respective genes (together with others still to be identified) make up a regulon that mediates uptake and utilization of the abovementioned amino acids.

Asparaginase↗
PubMed1975

Stimulation of the cell-free adenylate cyclase from guinea pig cerebral cortex by acidic amino acids and veratridine.

Vesicles from guinea pig cerebral cortex prepared by homogenization in Krebs-Ringer buffer contained adenylate cyclase activity which was stimulated by the acidic amino acids, cysteine sulfinic and glutamic acids, and by norepinephrine as well as by an alkaloid, veratridine. With these vesicular preparations the concentrations of amino acids required for half-maximal stimulation were about 30 muM, only about 1/30 those necessary with intact-cell preparations. Nearly additive effects were observed when either of the active amino acids was combined with norepinephrine at their optimal concentrations.

Adenylyl Cyclases↗
PubMed2006

The AauR-AauS two-component system regulates uptake and metabolism of acidic amino acids in Pseudomonas putida.

Pseudomonas putida KT2440 metabolizes a wide range of carbon and nitrogen sources, including many amino acids. In this study, a sigma54-dependent two-component system that controls the uptake and metabolism of acidic amino acids was identified. The system (designated aau, for acidic amino acid utilization) involves a sensor histidine kinase, AauS, encoded by PP1067, and a response regulator, AauR, encoded by PP1066. aauR and aauS deletion mutants were unable to efficiently utilize aspartate (Asp), glutamate (Glu), and glutamine (Gln) as sole sources of carbon and nitrogen. Growth of the mutants was partially restored when the above-mentioned amino acids were supplemented with glucose or succinate as an additional carbon source. Uptake of Gln, Asp, and asparagine (Asn) by the aauR mutant was moderately reduced, while Glu uptake was severely impaired. In the absence of glucose, the aauR mutant even secreted Glu into the medium. Furthermore, disruption of aauR affected the activities of several key enzymes of Glu and Asp metabolism, leading to the intracellular accumulation of Glu and greatly reduced survival times under conditions of nitrogen starvation. By a proteomics approach, four major proteins were identified that are downregulated during growth of the aauR mutant on Glu. Two of these were identified as periplasmic glutaminase/asparaginase and the solute-binding protein of a Glu/Asp transporter. Transcriptional analysis of lacZ fusions containing the putative promoter regions of these genes confirmed that their expression is indeed affected by the aau system. Three further periplasmic solute-binding proteins were strongly expressed during growth of the aauR deletion mutant on Glu but downregulated during cultivation on glucose/NH4+. These systems may be involved in amino acid efflux.

Amino Acids, Acidic↗
PubMed1983

A kinetic analysis of the release of acidic amino acids from rat cortical synaptosomes following pre-loading with [14C]glutamic acid.

The kinetics of the release of acidic amino acids have been studied in rat cortical synaptosomes. After pre-loading for 30 minutes in labeled glutamate, labeled glutamate and aspartate appear to be totally releasable. However, extra-synaptosomal Ca does not facilitate release. When elevated [K]0 was used to depolarize, release was unaffected by removal of Ca from the incubation medium. When veratridine was used as a depolarizing agent, presence of Ca in the incubation medium inhibited release. In all solutions, semi-log plots of synaptosomal label content as a function of time were non-linear, which is incompatible with release from a single compartment. Previous studies of the effect of membrane potential on transport led to the development of a carrier model which should participate in depolarization induced release (19). Under the conditions used in the present studies, this carrier should be saturated. When the data were fitted to a two compartment model, with release from compartment A linear with compartment size and release from compartment B via a saturated carrier, an excellent fit was obtained. Under control conditions, about 90% of the labeled amino acid is in compartment B and about 70% of the total release is from this compartment. Rate of release is greatly accelerated in depolarizing solutions. Under depolarizing conditions, there is a large shift of labeled amino acid from compartment B to compartment A and release from compartment A predominates. Analysis of the results under the several depolarizing conditions used shows that the present results are consistent with the predictions of the carrier model which has been developed from previous studies of the Na and membrane potential dependence of glutamate transport.

Amino Acids↗