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Amino Acids: The Forum for Amino Acid, Peptide and Protein Research (v.18, #1)
Regulation of Growth Hormone (GH) secretion by different glutamate receptor subtypes in the rat by M. Tena-Sempere; L. Pinilla; L. C. González; E. Aguilar (pp. 1-16).
It has been firmly established that excitatory amino acids (EAAs), such as glutamate, are pivotal elements in the hypothalamic circuitry involved in the control of pituitary function. The actions of EAAs are mediated by different postsynaptic receptor subtypes, which include N-methyl D-aspartate (NMDA), kainate (KA), 2-amino-3-hydroxy-5 methyl-4-isoxazol propionic acid (AMPA) and metabotropic receptors. In this review, we summarize our experimental work on the role of EAA neurotransmission in the control of GH secretion in the rat. Detailed characterization of the effects of agonists and antagonists of glutamate receptors on GH release revealed that activation of NMDA, KA and AMPA receptors at different age-points resulted in clear-cut stimulation of GH secretion, although age- and sex-dependent differences were detected in the pattern of response to the different agonists. This stimulatory action was proven nitric oxide (NO)-dependent and not exerted at the pituitary level. In addition, evaluation of the role of hypothalamic GH-releasing hormone (GHRH) in the stimulatory action of NMDA by means of immunoneutralization of endogenous GHRH or destruction of GHRH producing neurons suggested the involvement of signals other than GHRH in this response. Further, evidence was obtained on the modulation of the EAA system by gonadal factors, and on the physiological relevance of EAA pathways in the regulation of pulsatile GH release. In conclusion, our data using the rat as animal model provide evidence for a pivotal role of glutamate pathways in the regulation of GH secretion throughout the life-span.
Keywords: Keywords: Amino acids – Growth Hormone (GH) – Glutamate – Excitatory amino acids – Inhibitory amino acids – NMDA – KA – AMPA – Receptor – Rat
Taurine release modified by GABAergic agents in hippocampal slices from adult and developing mice by P. Saransaari; S. S. Oja (pp. 17-30).
In order to characterize the possible regulation of taurine release by GABAergic terminals, the effects of several agonists and antagonists of GABA receptors on the basal and K+-stimulated release of [3H]taurine were investigated in hippocampal slices from adult (3-month-old) and developing (7-day-old) mice using a superfusion system. Taurine release was concentration-dependently potentiated by GABA, which effect was reduced by phaclofen, saclofen and (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA) at both ages, suggesting regulation by both GABAB and GABAC receptors. The involvement of GABAA receptors could not be excluded since the antagonist bicuculline was able to affect both basal and K+-evoked taurine release. Furthermore, several GABAB receptor effectors were able to inhibit K+-stimulated taurine release in the adults, while the GABAC receptor agonists trans-4-aminocrotonic acid (TACA) and cis-4-aminocrotonic acid (CACA) potentiated this release. The potentiation of taurine release by agents acting on the three types of GABA receptors in both adult and developing hippocampus further indicates the involvement of transporters operating in an outward direction. This inference is corroborated by the moderate but significant inhibition of taurine uptake by the same compounds.
Keywords: Keywords: Amino acids – Taurine release – GABA receptors – Hippocampal slices – Adult – Developing mouse
Cerebral organic acid disorders induce neuronal damage via excitotoxic organic acids in vitro by S. Kölker; B. Ahlemeyer; J. Krieglstein; G. F. Hoffmann (pp. 31-40).
Glutaryl-CoA dehydrogenase deficiency (GDD), which is one of the most frequent organic acid disorders, is characterized by a specific age- and regional-dependent neuropathology. We hypothesized that the distinct brain damage in GDD could be caused by the main pathologic metabolites, the organic acids glutaric (GA) and 3-hydroxyglutaric (3-OH-GA) acids, through an excitotoxic sequence. Therefore, we investigated the effects of 3-OH-GA and GA on primary neuronal cultures from chick embryonic telencephalons. Here we report that 3-OH-GA and GA decreased cell viability concentration- and time-dependently, which could be only totally prevented by preincubation with MK-801, ifenprodil and NR2B antibodies. Furthermore, cell viability decreased in parallel with the increasing expression of NR2B subunit on cultured neurons from 2nd to 6th DIV. We conclude that GA and 3-OH-GA act as excitotoxic organic acids (EOA) specifically through NR1/NR2B and that the extent of induced neurotoxicity is dependent on NR1/NR2B expression during maturation.
Keywords: Keywords: Amino acids – Organic acids – Glutaryl-CoA dehydrogenase deficiency – Excitotoxicity – NMDA receptor
Synthesis and biological activity of canavanine hydrazide derivatives by J. Miersch; K. Grancharov; T. Pajpanova; S. Tabakova; S. Stoev; G.-J. Krauss; E. Golovinsky (pp. 41-59).
The canavanine derivatives L-canavanine hydrazide (CH), L-canavanine-bis-(2-chloroethyl)hydrazide (CBCH) and L-canavanine phenylhydrazide (CPH) were synthesized and evaluated for biological activity in microorganisms, plants and tumor cells using canavanine as a positive control. (1) In microbial systems, the compounds exerted activity, as assessed in 14 bacterial strains. The effect of canavanine was easily removed by equimolar concentrations of arginine or ornithine, while the effect of CBCH or CPH was abolished by 10-fold excess of arginine or 10- to 100-fold excess of ornithine. (2) In plants, the activity of CH and CBCH were relatively low, whereas the inhibitory potential of CPH was comparable or even superior to that of canavanine, resulting at 1 mM concentration in a nearly complete block of tomato cell growth, and reducing by up to 80% the length of radicles of cress, amaranth, cabbage and pumpkin. (3) In pumpkin seeds, CPH or canavanine induced the synthesis of four small heat shock proteins of hsp-17 family in the pH range of 6 to 7.5. The proteins exhibited in both cases a similar profile, but differed in the timing of their expression and/or accumulation. With canavanine, the highest hsp-17 expression was found after 48 h of drug treatment, while with CPH this maximum was shifted to 24 h. (4) CPH proved to be highly cytotoxic against Friend leukemia cells in culture, exceeding by one order of magnitude the cytotoxicity of canavanine. The effect of canavanine was completely removed in the presence of equimolar amounts of arginine, while a 20-fold excess of arginine failed to abolish the cytotoxicity of CPH. Thus, a proper hydrazide modification of canavanine may lead to a significant increase in its growth-inhibitory activity and to a change in the mode of action of the parent compound.
Keywords: Keywords: Amino acids – Canavanine hydrazide derivatives – Inhibitory activity – Microorganisms – Plants – Tumor cells – Heat-shock proteins
Identification of an oxidation product of aminoethylcysteine ketimine dimer by L. Pecci; A. Antonucci; F. Pinnen; D. Cavallini (pp. 61-67).
In continuation of our previous work dedicated to the detection of the oxidation products of aminoethylcysteine ketimine dimer by oxygen reactive species, we give here data for the identification of the α, β unsaturated sulfoxide as the main product of interaction of the dimer with H2O2. Identification has been done on the basis of mass spectrometry and NMR analyses of the product isolated by preparative chromatography.
Keywords: Keywords: Amino acids – Aminoethylcysteine ketimine dimer – Hydrogen peroxide – Sulfoxide derivative – Mass spectrometry – NMR analysis
The binding of amino acids to the herbicide 2,4-dichlorophenoxy acetic acid by E. Forgács; T. Cserháti; I. Barta (pp. 69-79).
The interaction of amino acids with the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was studied by charge-transfer chromatography carried out on diatomaceous layers covered with different amount of 2,4-D and the effect of salts on the strength of interaction was elucidated. It was established that Arg, His, Lys, Orn, Phe and Trp binds to 2,4-D, the binding process is of saturation character. Principal component analysis proved that the concentration of 2,4-D exerts the highest impact on the interaction and the effect of salts is of secondary importance. The results suggest that these amino acid residues may account for the binding of 2,4-D to proteins and can play a considerable role in the detoxification processes by forming conjugates with 2,4-D.
Keywords: Keywords: Amino acids – 2,4-Dichlorophenoxyacetic acid – Polar interaction – Charge-transfer chromatography
Stereospecific synthesis of α-methylated amino acids by S. Mzengeza; T. K. Venkatachalam; M. Diksic (pp. 81-88).
Both 2,5-trans and 2,5-cis disubstituted 2-tert-butyl-5-(indol-3-yl)methylimidazolidin-4-ones were synthesised and their enolates were prepared using LDA. While the enolate of the 2,5-trans disubstituted derivative could not be methylated, the enolate of the cis-2,5-disubstituted derivative was successfully methylated with methyl iodide to a product which on hydrolysis gave enantiomerically pure α-methyl-L-tryptophan.
Keywords: Keywords: Amino acids –α-Methyl-L-tryptophan – Stereospecific synthesis –α-Methyl-L-phenylalanine – 2-tert-butylimidazolidin-4-one
Derivatives of glutamic acid as new surfactants> by L. Rodehüser; H. Chaumette; A. Meyers; E. Rogalska; Ch. Gérardin; C. Selve (pp. 89-100).
Starting from glutamic acid, different types of surfactants have been synthesised by using original trimodular strategies. Monosubstituted zwitterionic amides of glutamic acid obtained with excellent yields show good surface activity.The grafting of a second hydrophobic side-chain leads to bicatenar cationic surfactants or to disubstituted nonionic cyclic compounds. In order to reduce the hydrophobic character of the bicatenar surfactants, a second synthetic method has been developed, allowing the introduction of a polar sugar group into these molecules.The surfactant properties of several of the products have been determined by physico-chemical methods such as surface tension measurements and compression isotherm studies by means of a Langmuir balance.
Keywords: Keywords: Amino acids – Glutamic acid – Surfactant – Amide – Imide – Critical concentration