Glutamate: An Amino Acid of Particular Distinction

Young, Vernon R.; Ajami, Alfred M.

doi:10.1093/jn/130.4.892s

Cited by 113 publications

(88 citation statements)

References 68 publications

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“…We propose that the high dose (1 mg/kg) initially overwhelmed the threshold of the liver to biotransform the MSG, but following establishment of tolerance a reduced activity (hepato-protective effect) of the MSG was then observed. This subsequent lowering of serum AST activity may also have arisen from the ability of enterocytes to "mop up" MSG by using it as oxidative fuel (Young and Ajami 2000), and thereby reducing its bioavailability.…”

Section: Discussionmentioning

confidence: 99%

The effects of monosodium l-glutamate administration on the reproduction and serum biochemistry of adult male rabbits

Okoye¹,

Ochiogu²,

Onah³

2016

Vet. Med. - Czech

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ABSTRACT:In this study the effects of monosodium l-glutamate (MSG) administration on the reproductive parameters and serum biochemistry of male rabbits were investigated. Sixteen mature male New Zealand mixed-breed of rabbits (Oryctolagus species) weighing 1.1-1.65 kg were used for this study. They were randomised into four groups of four rabbits each. Group A which served as the untreated control, received only distilled water while Groups B, C and D which were the treated groups, received 0.25 g/kg, 0.5 g/kg and 1 g/kg body weight of MSG from a 40% MSG stock solution. The MSG was administered to the rabbits by oral gavage every forty-eight hours for a period of eight weeks. Serum levels of luteinising hormone (LH), testosterone, total cholesterol and total protein, and activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were evaluated on Days 14, 28 and 56 of MSG administration. Results showed that when compared to the untreated group (Group A), on Day 56 of MSG administration the mean serum levels of both LH and testosterone were significantly (P < 0.05) lower in Group D that received 1 g/kg body weight MSG, while the serum cholesterol levels of Group C rabbits that received 0.5 g/kg body weight MSG was significantly (P < 0.05) lower on Day 28 of MSG administration. The mean serum ALT activity of Groups B and C rabbits were significantly (P < 0.05) lower on Day 56 of MSG administration, while the mean serum AST activity of the Group D rabbits was significantly (P < 0.05) higher on Day 14 of MSG administration. There were no significant (P > 0.05) variations in the mean serum total protein between the groups. Testicular histomorphology revealed that MSG administration did not affect the testes of the rabbits as there was no obvious testicular histopathology. It was concluded that administration of MSG to male rabbits significantly lowered serum LH, testosterone and cholesterol levels and serum ALT activity without affecting testicular histomorphology.

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Section: Discussionmentioning

confidence: 99%

The effects of monosodium l-glutamate administration on the reproduction and serum biochemistry of adult male rabbits

Okoye¹,

Ochiogu²,

Onah³

2016

Vet. Med. - Czech

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“…2,16) Because intestinal mucosa cells metabolize virtually all enteral GLU during absorption, blood levels of GLU do not rise appreciably after food ingestion. Figure 2 shows diurnal levels of GLU in the blood and brain of rats fed 30% casein protein diet.…”

Section: Visceral Mechanismsmentioning

confidence: 99%

“…As an essential substrate in the intermediary metabolism, free GLU is present in the most organs and tissues (skeletal muscles, brain, kidneys, and liver) in substantial concentrations. 1,2) GLU plays an important role in the energy metabolism and synthesis of other amino acids, glutathione, and proteins. In the brain, GLU acts as a major excitatory neurotransmitter and its activity regulates synaptic plasticity, learning, memory, motor activity, and neural development.…”

Section: Introductionmentioning

confidence: 99%

Brain Activation by Umami Substances via Gustatory and Visceral Signaling Pathways, and Physiological Significance

Kondoh

Torii

2008

Biological & Pharmaceutical Bulletin

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Monosodium L-glutamate (MSG) elicits a unique taste termed umami and is widely used as a flavor enhancer in a variety of cuisines. Recent studies suggest the existence of L-glutamate (GLU) receptors and its transduction molecules in the gut mucosa as well as in the oral cavity. The vagal gastric afferent fibers respond specifically to the luminal stimulation of GLU in the stomach. GLU administration in the stomach also activates several brain areas (insular cortex, basal ganglia, limbic system, and hypothalamus). Ingestion of MSG enhanced secretion of digestive juices and insulin. Spontaneous ingestion of an MSG solution at the most preferred concentration (1% (w/v)) reduced weight gain, fat deposition, and plasma leptin levels without affecting food intake, naso-anal length (an index of somatic development), and lean mass in rats. These results suggest that umami signaling via gustatory and visceral pathways may play an important role in the process of digestion, absorption, metabolism, and other physiological functions via activation of the brain.

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“…8) seems counterintuitive because of the larger mass of L-glutamate. However, it has been demonstrated that the distance between the oxygens of the two carboxyl groups of aspartate is in fact larger than that of glutamate (41). Although it appears that DHK can protect at some positions without the involvement of conformational changes, its binding is likely to induce the movement of other residues.…”

Section: Activity and Accessibility Of Singlementioning

confidence: 99%

Cysteine-scanning Mutagenesis Reveals a Conformationally Sensitive Reentrant Pore-Loop in the Glutamate Transporter GLT-1

Grunewald

Menaker

Kanner

2002

Journal of Biological Chemistry

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Removal of glutamate from the synaptic cleft by (Na ؉ ؉ K ؉ )-coupled transporters prevents neurotoxicity due to elevated concentrations of the transmitter. These transporters exhibit an unusual topology, including two reentrant loops. Reentrant loop II plays a pivotal role in coupling ion and glutamate fluxes. Here we used cysteine-scanning mutagenesis of the GLT-1 transporter to test the idea that this loop undergoes conformational changes following sodium and substrate binding. 15 of 22 consecutive single cysteine mutants in the stretch between Gly-422 and Ser-443 exhibited 30 -100% of the transport activity of the cysteine-less transporter when expressed in HeLa cells. The transport activity of 11 of the 15 active mutants including five consecutive residues in the ascending limb was inhibited by small hydrophilic methanethiosulfonate reagents. The sensitivity of seven cysteine mutants, including A438C and S440C, to the reagents was significantly reduced by sodium ions, but the opposite was true for A439C. The non-transportable analogue dihydrokainate protected at almost all positions throughout the loop, and at two of the positions, the analogue protected even in the absence of sodium. Our results indicate that reentrant loop II forms part of an aqueous pore, the access of which is blocked by the glutamate analogue dihydrokainate, and that sodium influences the conformation of this pore-loop.Glutamate transporters in the brain ensure that the synaptic levels of the transmitter are kept below the neurotoxic levels (1-6). These transporters, located in the plasma membrane of nerve and glial cells, play an important role in limiting the duration of synaptic excitation (7-10). The uptake process is electrogenic (11-13), involving co-transport of three sodium ions, a proton, and a glutamate molecule and countertransport of a potassium ion (14 -16). In addition to the coupled flux, glutamate transporters mediate a thermodynamically uncoupled chloride flux activated by two of the molecules they transport, sodium and glutamate (17, 18).The five known eukaryotic glutamate transporters, GLT-1 (19), GLAST-1 (20), EAAC-1 (21), , and EAAT-5 (22), have an overall amino acid identity of ϳ50%. The homology is significantly higher in the carboxyl-terminal half of the transporters. Topology studies suggest that this region of the protein has an intriguing arrangement containing two oppositely oriented reentrant loops, the two transmembrane domains (TMs) 1 7 and 8, and an outward-facing hydrophobic region (Refs. 23-25, and see Fig. 1). Some of the features of the membrane topology remain under debate (26).Several amino acid residues critical for the function of glutamate transporters are located in the carboxyl-terminal half. Two adjacent amino acid residues of GLT-1, Tyr-403 and Glu-404, are located in TM7 (Fig. 1) and are conserved in all other glutamate transporters. Both were implicated in the binding of potassium ions (16,27) and appear to be close to one of the sodium binding sites (27). A conserved arginine residue, Arg...

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Glutamate: An Amino Acid of Particular Distinction

Cited by 113 publications

References 68 publications

The effects of monosodium l-glutamate administration on the reproduction and serum biochemistry of adult male rabbits

The effects of monosodium l-glutamate administration on the reproduction and serum biochemistry of adult male rabbits

Brain Activation by Umami Substances via Gustatory and Visceral Signaling Pathways, and Physiological Significance

Cysteine-scanning Mutagenesis Reveals a Conformationally Sensitive Reentrant Pore-Loop in the Glutamate Transporter GLT-1

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