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Annals of Nutrition & Metabolism 2018Glutamate is a non-essential amino acid at the crossroads of nitrogen and energy metabolism. Glutamate metabolism is characterized by reactions that may be anabolic or... (Review)
Review
BACKGROUND
Glutamate is a non-essential amino acid at the crossroads of nitrogen and energy metabolism. Glutamate metabolism is characterized by reactions that may be anabolic or catabolic in nature depending on the tissue (i.e., glutamate dehydrogenase, transaminases), and it can also be either the precursor or the metabolite of glutamine. Unlike glutamine, which is the form of interorgan ammonia transport, glutamate metabolism is mostly compartmentalized within the cells, its interorgan exchanges being limited to a flux from liver to muscle.
SUMMARY
Glutamate catabolism is extremely intense in the splanchnic area, such that after a meal (rich in proteins) almost no glutamate appears in the systemic circulation. However, this process is saturable as after glutamate loading at a high dose level, glutamate appears dose-dependently in the circulation. This systemic glutamate -appearance is blunted if glutamate is co-ingested with a carbohydrate source. Key Messages: The underlying reason for this highly specific metabolism is that glutamate plays a key role in nitrogen homeostasis, and the organism does all it can to limit the bioavailability of glutamate, which can be neurotoxic in excess. As glutamate is never eaten alone, its bioavailability will be limited if not negligible, and no adverse effects are to be expected in adult humans.
Topics: Adult; Animals; Diet; Glutamate Decarboxylase; Glutamate Dehydrogenase; Glutamic Acid; Humans; Liver; Muscles
PubMed: 30508813
DOI: 10.1159/000494776 -
Molecules (Basel, Switzerland) Feb 2020Glutamate decarboxylase (GAD; EC 4.1.1.15) is a unique pyridoxal 5-phosphate (PLP)-dependent enzyme that specifically catalyzes the decarboxylation of L-glutamic acid to...
Glutamate decarboxylase (GAD; EC 4.1.1.15) is a unique pyridoxal 5-phosphate (PLP)-dependent enzyme that specifically catalyzes the decarboxylation of L-glutamic acid to produce γ-aminobutyric acid (GABA), which exhibits several well-known physiological functions. However, glutamate decarboxylase from different sources has the common problem of poor thermostability that affects its application in industry. In this study, a parallel strategy comprising sequential analysis and free energy calculation was applied to identify critical amino acid sites affecting thermostability of GAD and select proper mutation contributing to improve structure rigidity of the enzyme. Two mutant enzymes, D203E and S325A, with higher thermostability were obtained, and their semi-inactivation temperature (T) values were 2.3 °C and 1.4 °C higher than the corresponding value of the wild-type enzyme (WT), respectively. Moreover, the mutant, S325A, exhibited enhanced activity compared to the wild type, with a 1.67-fold increase. The parallel strategy presented in this work proved to be an efficient tool for the reinforcement of protein thermostability.
Topics: Amino Acid Sequence; Amino Acids; Glutamate Decarboxylase; Mutation; Sequence Alignment; Temperature
PubMed: 32041144
DOI: 10.3390/molecules25030690 -
Journal of Nutritional Science and... 2019Glutamate decarboxylase (GAD) is an important enzyme in biological metabolisms acting on catalyzing the irreversible α-decarboxylation of L-glutamic acid to...
Glutamate decarboxylase (GAD) is an important enzyme in biological metabolisms acting on catalyzing the irreversible α-decarboxylation of L-glutamic acid to γ-aminobutyric acid (GABA) and CO, which was focused in this study. Three rice varieties different in color were germinated at different times and used for crude GAD extraction. Crude GADs with an optimal germination time from germinated black (GBR), red (GRR), and white (GWR) rice were evaluated for enzymatic properties, including the effect of pHs, temperatures, and concentrations of both L-glutamic acid and pyridoxal 5'-phosphate (PLP). Crude GAD with optimum enzymatic properties was selected to be partially purified using ammonium sulfate (AMS) precipitation. The obtained GAD was supplemented to soymilk and determined for GABA content. All crude GADs from germinated rice at 10 germination days presented the highest enzyme activity. For enzymatic properties, crude GADs showed the highest activity at pH in a range of 5.6-6.0 at 60ºC. The Km values of crude GADs were in the range of 7.68-8.06 mM for L-glutamic acid and 0.15-0.20 μM for PLP and were the lowest in crude GAD from GBR. GAD from GBR presented the highest enzyme activity in the fraction with 50% saturation (v/v) after AMS precipitation and it was purified for 14.61 folds. The addition of this GAD (1.0%, v/v) resulted in the increasing of GABA content in soymilk to 53.79 mg/100 mL, accounted for 1.23 times compared with control.
Topics: Carbon Dioxide; Carboxy-Lyases; Decarboxylation; Dietary Supplements; Germination; Glutamate Decarboxylase; Glutamic Acid; Oryza; Pyridoxal Phosphate; Soy Milk; gamma-Aminobutyric Acid
PubMed: 31619621
DOI: 10.3177/jnsv.65.S166 -
Molecular Biology Reports Oct 2010A major pathway of beta-alanine synthesis in insects is through the alpha-decarboxylation of aspartate, but the enzyme involved in the decarboxylation of aspartate has...
A major pathway of beta-alanine synthesis in insects is through the alpha-decarboxylation of aspartate, but the enzyme involved in the decarboxylation of aspartate has not been clearly defined in mosquitoes and characterized in any insect species. In this study, we expressed two putative mosquito glutamate decarboxylase-like enzymes of mosquitoes and critically analyzed their substrate specificity and biochemical properties. Our results provide clear biochemical evidence establishing that one of them is an aspartate decarboxylase and the other is a glutamate decarboxylase. The mosquito aspartate decarboxylase functions exclusively on the production of beta-alanine with no activity with glutamate. Likewise the mosquito glutamate decarboxylase is highly specific to glutamate with essentially no activity with aspartate. Although insect aspartate decarboxylase shares high sequence identity with glutamate decarboxylase, we are able to closely predict aspartate decarboxylase from glutamate decarboxylase based on the difference of their active site residues.
Topics: Animals; Carboxy-Lyases; Culicidae; Electrophoresis, Polyacrylamide Gel; Glutamate Decarboxylase; Kinetics; Spectrum Analysis; Substrate Specificity
PubMed: 19842059
DOI: 10.1007/s11033-009-9902-y -
International Journal of Molecular... Apr 2022Two isoforms of the glutamate decarboxylase (GAD) enzyme exist, GAD65 and GAD67, which are associated with type 1 diabetes (T1D) and stiff-person syndrome (SPS),...
Two isoforms of the glutamate decarboxylase (GAD) enzyme exist, GAD65 and GAD67, which are associated with type 1 diabetes (T1D) and stiff-person syndrome (SPS), respectively. Interestingly, it has been reported that T1D patients seldom develop SPS, whereas patients with SPS occasionally develop T1D. In addition, coxsackievirus B4 (CVB4) has previously been proposed to be involved in the onset of T1D through molecular mimicry. On this basis, we aimed to examine antibody cross-reactivity between a specific region of GAD65 and GAD67, which has high sequence homology to the nonstructural P2C protein of CVB4 to determine potential correlations at antibody level. Monoclonal peptide antibodies generated in mice specific for a region with high similarity in all three proteins were screened for reactivity along with human sera in immunoassays. In total, six antibodies were generated. Two of the antibodies reacted to both GAD isoforms. However, none of the antibodies were cross-reactive to CVB, suggesting that antibody cross-reactivity between GAD65 and CVB, and GAD67 and CVB may not contribute to the onset of T1D and SPS, respectively.
Topics: Animals; Antibodies, Monoclonal; Autoantibodies; Diabetes Mellitus, Type 1; Glutamate Decarboxylase; Humans; Mice; Peptides; Protein Isoforms; Stiff-Person Syndrome
PubMed: 35457242
DOI: 10.3390/ijms23084424 -
Journal of Applied Microbiology Jan 2013Glutamate plays a central role in a wide range of metabolic processes in bacterial cells. This review focuses on the involvement of glutamate in bacterial stress... (Review)
Review
Glutamate plays a central role in a wide range of metabolic processes in bacterial cells. This review focuses on the involvement of glutamate in bacterial stress responses. In particular, it reviews the role of glutamate metabolism in response against acid stress and other stresses. The glutamate decarboxylase (GAD) system has been implicated in acid tolerance in several bacterial genera. This system facilitates intracellular pH homoeostasis by consuming protons in a decarboxylation reaction that produces γ-aminobutyrate (GABA) from glutamate. An antiporter system is usually present to couple the uptake of glutamate to the efflux of GABA. Recent insights into the functioning of this system will be discussed. Finally, the intracellular fate of GABA will also be discussed. Many bacteria are capable of metabolizing GABA to succinate via the GABA shunt pathway. The role and regulation of this pathway will be addressed in the review.
Topics: Acids; Antiporters; Bacteria; Glutamate Decarboxylase; Glutamic Acid; Stress, Physiological; Succinic Acid; gamma-Aminobutyric Acid
PubMed: 22924898
DOI: 10.1111/j.1365-2672.2012.05434.x -
Transcription 2012Gad2 encodes GAD65, which is present preferentially in presynaptic terminals for synthesis of GABA for vesicle release. Gad2 is a regulatory target of cell activities in... (Review)
Review
Gad2 encodes GAD65, which is present preferentially in presynaptic terminals for synthesis of GABA for vesicle release. Gad2 is a regulatory target of cell activities in various brain functions and in GABA perturbation-related neurological diseases. However, our understanding of how Gad2 is transcriptionally regulated and how Gad2 transcription responds to changing cell environment under these conditions is still limited. This review discusses recent advances in the regulatory mechanisms for Gad2 transcription and highlights the characteristics of TATA-less Gad2 promoters and regulation of Gad2 transcription by CREB and by activity-dependent epigenetic modification of the chromatin structure in regulatory elements of the Gad2 gene.
Topics: Enhancer Elements, Genetic; Gene Expression Regulation, Enzymologic; Glutamate Decarboxylase; Humans; Promoter Regions, Genetic; Transcription Factors; Transcription, Genetic; gamma-Aminobutyric Acid
PubMed: 22414751
DOI: 10.4161/trns.19511 -
Pediatric Diabetes Jul 2016The autoimmune destruction of beta cells, resulting in clinical type 1 diabetes, may start early in life and last for several months or years. During this period of... (Review)
Review
BACKGROUND
The autoimmune destruction of beta cells, resulting in clinical type 1 diabetes, may start early in life and last for several months or years. During this period of time, we have an opportunity to try to prevent or delay further beta-cell destruction and clinical onset of type 1 diabetes.
OBJECTIVES
Ongoing prediction and prevention studies in Skåne, Sweden are described.
METHODS
During September 2000 to August 2004, 35 000 children were screened at birth for genetic type 1 diabetes risk in the Diabetes Prediction in Skåne Study (DiPiS). In August 2004, the screening continued within the Enviromnental Determinants of Diabetes in the Young study (TEDDY). In the clinical trial Diabetes Prevention - Immune Tolerance (DiAPREV-IT), children with multiple islet autoimmunity have been included to investigate if immune tolerance with Alum-formulated GAD65 may prevent further beta-cell loss.
RESULTS
In DiPiS and TEDDY, a large number of children are followed in order to find the factors that trigger the autoimmune process leading to type 1 diabetes. Children followed in the studies develop diabetes at an early stage of disease, with few symptoms and a low frequency of diabetes ketoacidosis. DiAPREV-IT is still blinded and results will be available in December 2016.
CONCLUSION
Large prospective studies will be needed to understand the complex process leading to type 1 diabetes. Secondary prevention may be possible in children with islet autoimmunity, but the studies are complicated by the variability of glucose metabolism and beta-cell loss.
Topics: Diabetes Mellitus, Type 1; Glutamate Decarboxylase; Humans; Immune Tolerance; Secondary Prevention; Sweden
PubMed: 27411440
DOI: 10.1111/pedi.12325 -
Journal of Chemical Neuroanatomy Oct 2022The inhibitory amino acid transmitter γ-aminobutryic acid (GABA) acts within the ventromedial hypothalamus to regulate systemic glucose homeostasis, but the issue of...
Single-cell multiplex qPCR evidence for sex-dimorphic glutamate decarboxylase, estrogen receptor, and 5'-AMP-activated protein kinase alpha subunit mRNA expression by ventromedial hypothalamic nucleus GABAergic neurons.
The inhibitory amino acid transmitter γ-aminobutryic acid (GABA) acts within the ventromedial hypothalamus to regulate systemic glucose homeostasis, but the issue of whether this neurochemical signal originates locally or is supplied by afferent innervation remains controversial. Here, combinatory in situ immunocytochemistry/laser-catapult microdissection/single-cell multiplex qPCR techniques were used to investigate the premise that ventromedial hypothalamic nucleus ventrolateral (VMNvl) and/or dorsomedial (VMNdm) division neurons contain mRNAs that encode glutamate decarboxylase (GAD) or GAD and metabolic-sensory biomarkers, and that expression of these genes is sex-dimorphic. In male and female rats, GAD mRNA was elevated in VMNvl versus VMNdm GAD-immunopositive (-ir) neurons, yet the female exhibited higher GAD transcript content in VMNdm versus VMNvl GABAergic nerve cells. Estrogen receptor (ER)-alpha transcripts were lower in female versus male GABA neurons from either VMN division; ER-beta and G-protein-coupled ER-1 mRNA expression profiles were also comparatively reduced in cells from female versus male VMNvl. VMNvl and VMNdm GAD-ir-positive neurons showed equivalent levels of glucokinase and sulfonylurea receptor-1 mRNA between sexes. 5'-AMP-activated protein kinase-alpha 1 (AMPK) and -alpha 2 (AMPK) transcripts were lower in female versus male VMNdm GABAergic neurons, yet AMPK mRNA levels were higher in cells acquired from female versus male VMNvl. Current studies document GAD and - gene expression in VMNvl and VMNdm GAD-ir-positive neurons in each sex. Results infer that GABAergic neurons in each division may exhibit sex differences in receptiveness to estradiol. Outcomes also support the prospect that energy sensory function by this neurotransmitter cell type may predominate in the VMNvl in female versus VMNdm in the male.
Topics: AMP-Activated Protein Kinases; Animals; Estrogen Receptor alpha; Female; GABAergic Neurons; Glutamate Decarboxylase; Male; RNA, Messenger; Rats; Receptors, Estrogen; Ventromedial Hypothalamic Nucleus
PubMed: 35772680
DOI: 10.1016/j.jchemneu.2022.102132 -
Microbial Cell Factories Aug 2011Acid stress impacts the persistence of lactobacilli in industrial sourdough fermentations, and in intestinal ecosystems. However, the contribution of glutamate to acid...
BACKGROUND
Acid stress impacts the persistence of lactobacilli in industrial sourdough fermentations, and in intestinal ecosystems. However, the contribution of glutamate to acid resistance in lactobacilli has not been demonstrated experimentally, and evidence for the contribution of acid resistance to the competitiveness of lactobacilli in sourdough is lacking. It was therefore the aim of this study to investigate the ecological role of glutamate decarboxylase in L. reuteri.
RESULTS
A gene coding for a putative glutamate decarboxylase, gadB, was identified in the genome of L. reuteri 100-23. Different from the organization of genetic loci coding for glutamate decarboxylase in other lactic acid bacteria, gadB was located adjacent to a putative glutaminase gene, gls3. An isogenic deletion mutant, L. reuteri ∆gadB, was generated by a double crossover method. L. reuteri 100-23 but not L. reuteri ∆gadB converted glutamate to γ-aminobutyrate (GABA) in phosphate butter (pH 2.5). In sourdough, both strains converted glutamine to glutamate but only L. reuteri 100-23 accumulated GABA. Glutamate addition to phosphate buffer, pH 2.5, improved survival of L. reuteri 100-23 100-fold. However, survival of L. reuteri ∆gadB remained essentially unchanged. The disruption of gadB did not affect growth of L. reuteri in mMRS or in sourdough. However, the wild type strain L. reuteri 100-23 displaced L. reuteri ∆gadB after 5 cycles of fermentation in back-slopped sourdough fermentations.
CONCLUSIONS
The conversion of glutamate to GABA by L. reuteri 100-23 contributes to acid resistance and to competitiveness in industrial sourdough fermentations. The organization of the gene cluster for glutamate conversion, and the availability of amino acids in cereals imply that glutamine rather than glutamate functions as the substrate for GABA formation. The exceptional coupling of glutamine deamidation to glutamate decarboxylation in L. reuteri likely reflects adaptation to cereal substrates.
Topics: Acids; Bread; Fermentation; Food Microbiology; Glutamate Decarboxylase; Limosilactobacillus reuteri
PubMed: 21995488
DOI: 10.1186/1475-2859-10-S1-S8