Glutamate Research Papers - Academia.edu (original) (raw)

Amino acids are the essential building blocks of proteins and peptides. They can also take part in intermediary metabolism and act as precur- sors to common biogenic amine neurotransmitters. Certain amino acids act as neurotransmitters... more

Amino acids are the essential building blocks of proteins and peptides. They can also take part in intermediary metabolism and act as precur- sors to common biogenic amine neurotransmitters. Certain amino acids act as neurotransmitters and are the major excitatory (aspartate and glutamate) and inhibitory (GABA and taurine) commands in the central nervous system. The measurement of the profile of these neuroactive amino acids can assist with the characterization and our understanding of the factors and potential causes of various neurological conditions. Amino acids are difficult to detect directly as they lack a suitable chro - mophore, so derivatives are often prepared. A specific challenge of the analytical method is realized when analyses in low volume samples are at low concentrations, as is the case with brain microdialysis samples. Isoindole derivatives of amino acids, formed through a well-established reaction with o-phthalaldehyde (OPA) and 2-mercaptoethanol (β-ME), can now ...

Abstract: Many different bacterial species produce lipases which hydrolyze esters of glycerol with preferably long-chain fatty acids. They act at the interface generated by a hydrophobic lipid substrate in a hydrophilic aqueous medium. A... more

Abstract: Many different bacterial species produce lipases which hydrolyze esters of glycerol with preferably long-chain fatty acids. They act at the interface generated by a hydrophobic lipid substrate in a hydrophilic aqueous medium. A characteristic property of lipases is called interfacial activation, meaning a sharp increase in lipase activity observed when the substrate starts to form an emulsion, thereby presenting to the enzyme an interfacial area. As a consequence, the kinetics of a lipase reaction do not follow the classical Michaelis-Menten model. With only a few exceptions, bacterial lipases are able to completely hydrolyze a triacylglycerol substrate although a certain preference for primary ester bonds has been observed. Numerous lipase assay methods are available using coloured or fluorescent substrates which allow spectroscopic and fluorimetric detection of lipase activitiy. Another important assay is based on titration of fatty acids released from the substrate. Newly developed methods allow to exactly determine lipase activity via controlled surface pressure or by means of a computer-controlled oil drop tensiometer. The synthesis and secretion of lipases by bacteria is influenced by a variety of environmental factors like ions, carbon sources, or presence of non-metabolizable polysaccharides. The secretion pathway is known for Pseudomonas lipases with P. aeruginosa lipase using a two-step mechanism and P. fluorescens lipase using a one-step mechanism. Additionally, some Pseudomonas lipases need specific chaperone-like proteins assisting their correct folding in the periplasm. These lipase-specific foldases (Lif-proteins) which show a high degree of amino acid sequence homology among different Pseudomonas species are coded for by genes located immediately downstream the lipase structural genes. A comparison of different bacterial lipases on the basis of primary structure revealed only very limited sequence homology. However, determination of the three-dimensional structure of the P. glumae lipase indicated that at least some of the bacterial lipases will presumably reveal a conserved folding pattern called the α/β-hydrolase fold, which has been described for other microbial and human lipases. The catalytic site of lipases is buried inside the protein and contains a serine-protease-like catalytic triad consisting of the amino acids serine, histidine, and aspartate (or glutamate). The Ser-residue is located in a strictly conserved β-ε-Ser-α motif. The active site is covered by a lid-like a-helical structure which moves away upon contact of the lipase with its substrate, thereby exposing hydrophobic residues at the protein's surface mediating the contact between protein and substrate. This movable lid-like α-helix explains at a molecular level the lipase-specific phenomenon of interfacial activation. At least some of the pathogenic bacterial species produce a lipase which has been studied with respect to its role as a virulence factor. Lipases of Propionibacterium acnes and Staphylococcus epidermidis may be involved in colonization and persistence of these bacteria on the human skin. Lipases of S. aureus and P. aeruginosa are produced during the bacterial infection process and, at least in vitro, considerably impair the function of different cell types involved in the human immune response like macrophages or platelets. The present state of knowledge suggests to classify the lipases as important bacterial virulence factors which exert their harmful effects in combination with other bacterial enzymes, in particular the phospholipases C. Most of the steadily increasing interest in bacterial lipases is based on their biotechnological applications which are partly based on their potential to catalyze not only hydrolysis but also synthesis of a variety of industrially valuable products. Optically active compounds, various esters and lactones are among the substances synthesized using bacterial lipases. Recently, an important application emerged with the addition of bacterial lipases to household detergents in order to reduce or even replace synthetic detergent chemicals which pose considerable environmental problems. As a main conclusion, [ipases represent an extremely versatile group of bacterial extracellular enzymes that are capable of performing a variety of important reactions, thereby presenting a fascinating field tot future research.

Using acute and delayed in vitro ischaemia models we evaluated the neuroprotective efficacy of five peptides (PYC19D-TAT, PYC35D-TAT, PYC36D-TAT, PYC38D-TAT, PYC41D-TAT) previously demonstrated to down-regulate AP-1 activation (e.g.... more

Using acute and delayed in vitro ischaemia models we evaluated the neuroprotective efficacy of five peptides (PYC19D-TAT, PYC35D-TAT, PYC36D-TAT, PYC38D-TAT, PYC41D-TAT) previously demonstrated to down-regulate AP-1 activation (e.g. c-Jun/c-Fos activation), and inhibit neuronal death in vitro following glutamate and kainic acid excitotoxicity. The JNK inhibitor peptide (JNKI-1D-TAT) and the TAT cell-penetrating-carrier peptide (D-TAT) were used as controls. In the acute model, all five AP-1 inhibitory peptides, JNKI-1D-TAT, and D-TAT provided neuroprotection by increasing neuronal viability from ≈5 to 23–53%. In the delayed model, three of the five AP-1 inhibitory peptides (PYC35D-TAT, PYC36D-TAT, PYC38D-TAT) and JNKI-1D-TAT provided neuroprotection by increasing neuronal viability from ≈10 to 35–80%. This study not only highlights a group of peptides with therapeutic potential, but also the need to assess putative therapeutics in multiple in vitro models to achieve a comprehensive representation of their neuroprotective capacity.

The aim of this study was to investigate the possible involvement of the glutamatergic system in the toxicity of organochalcogens, since this is an important neurotransmitter system for signal transduction and neural function. The results... more

The aim of this study was to investigate the possible involvement of the glutamatergic system in the toxicity of organochalcogens, since this is an important neurotransmitter system for signal transduction and neural function. The results indicated that 100 μM diphenyl diselenide ( ...

In the central nervous system, astrocytes form an intimately connected network with neurons, and their processes closely enwrap synapses. The critical role of these cells in metabolic and trophic support to neurons, ion buffering and... more

In the central nervous system, astrocytes form an intimately connected network with neurons, and their processes closely enwrap synapses. The critical role of these cells in metabolic and trophic support to neurons, ion buffering and clearance of neurotransmitters is well established. However, recent accumulating evidence suggests that astrocytes are active partners of neurons in additional and more complex functions. In particular, astrocytes express a repertoire of neurotransmitter receptors mirroring that of neighbouring synapses. Such receptors are stimulated during synaptic activity and start calcium signalling into the astrocyte network. Intracellular oscillations and intercellular calcium waves represent the astrocyte’s own form of excitability, as they trigger release of transmitter (i.e. glutamate) via a novel process sensitive to blockers of exocytosis and involving cyclooxygenase eicosanoids. Astrocyte-released glutamate activates receptors on the surrounding neurons and modifies their electrical and intracellular calcium ([Ca2+]i) state. These exciting new findings reveal an active participation of astrocytes in synaptic transmission and the involvement of neuron-astrocyte circuits in the processing of information in the brain.

Hydra feeding response is a very primitive olfactory-like behavior present in a multicellular organism. We investigated the role of nitric oxide (NO) in the induction and control of hydra feeding response. Under basal conditions, hydra... more

Hydra feeding response is a very primitive olfactory-like behavior present in a multicellular organism. We investigated the role of nitric oxide (NO) in the induction and control of hydra feeding response. Under basal conditions, hydra specimens produce detectable amounts of nitrite (NO2-), the breakdown product of NO. When hydra were incubated with reduced glutathione (GSH), the typical activator of feeding response, an increase of basal NO production was observed. This effect was inhibited by glutamic or alpha-aminoadipic acids, two GSH antagonists, which block GSH-induced feeding response, and by the NO synthase (NOS) inhibitor L-NAME. Moreover, we found that hydra possess a calcium-dependent (but calmodulin-independent) NOS isoform. By using exogenous NO donors and NOS inhibitors, we demonstrated that NO stimulus can participate both in triggering tentacular movements and in recruiting neighbor tentacles during hydra feeding response. By using dbt2-cGMP, an analog to cGMP, we ob...