View source for Glutamate dehydrogenase

{{Short description|Hexameric enzyme}}
{{cs1 config|name-list-style=vanc}}
{{infobox enzyme
| Name       = glutamate dehydrogenase (GLDH)
| EC_number  = 1.4.1.2
| CAS_number = 9001-46-1
| GO_code    = 0004352
| image      =
| width      = 
| caption    =  
}}
{{infobox enzyme
| Name       = glutamate dehydrogenase [NAD(P)+]
| EC_number  = 1.4.1.3
| CAS_number = 9029-12-3
| GO_code    = 0004353
| image      =
| width      = 
| caption    =  
}}
{{infobox enzyme
| Name       = glutamate dehydrogenase (NADP+)
| EC_number  = 1.4.1.4
| CAS_number = 9029-11-2
| GO_code    = 0004354
| image      =
| width      = 
| caption    =  
}}

'''Glutamate dehydrogenase''' (GLDH, GDH) is an [[enzyme]] observed in both prokaryotes and eukaryotic  [[mitochondria]].  The aforementioned reaction also yields ammonia, which in eukaryotes is canonically processed as a substrate in the [[urea cycle]]. Typically, the α-ketoglutarate to glutamate reaction does not occur in mammals, as glutamate dehydrogenase equilibrium favours the production of ammonia and α-ketoglutarate. Glutamate dehydrogenase also has a very low affinity for ammonia (high [[Michaelis constant]] <math>K_m</math> of about 1 mM), and therefore toxic levels of ammonia would have to be present in the body for the reverse reaction to proceed (that is, α-ketoglutarate and ammonia to glutamate and NAD(P)+). In the brain, the NAD+/NADH ratio in brain mitochondria encourages oxidative deamination (i.e. glutamate to α-ketoglutarate and ammonia).<ref name="pmid27885627">{{cite book | vauthors = McKenna MC, Ferreira GC | chapter = Enzyme Complexes Important for the Glutamate–Glutamine Cycle | series = Advances in Neurobiology | title = The Glutamate/GABA-Glutamine Cycle | volume = 13 | pages = 59–98 | date = 2016 | pmid = 27885627 | doi = 10.1007/978-3-319-45096-4_4 | isbn = 978-3-319-45094-0 }}</ref> In bacteria, the ammonia is assimilated to amino acids via glutamate and aminotransferases.<ref name="Lightfoot_1988">{{cite journal | vauthors = Lightfoot DA, Baron AJ, Wootton JC | title = Expression of the Escherichia coli glutamate dehydrogenase gene in the cyanobacterium Synechococcus PCC6301 causes ammonium tolerance | journal = Plant Molecular Biology | volume = 11 | issue = 3 | pages = 335–44 | date = May 1988 | pmid = 24272346 | doi = 10.1007/BF00027390 | bibcode = 1988PMolB..11..335L | s2cid = 21845538 }}</ref> In plants, the enzyme can work in either direction depending on environment and stress.<ref name="pmid16046826">{{cite journal | vauthors = Mungur R, Glass AD, Goodenow DB, Lightfoot DA | title = Metabolite fingerprinting in transgenic Nicotiana tabacum altered by the Escherichia coli glutamate dehydrogenase gene | journal = Journal of Biomedicine & Biotechnology | volume = 2005 | issue = 2 | pages = 198–214 | date = June 2005 | pmid = 16046826 | pmc = 1184043 | doi = 10.1155/JBB.2005.198 | doi-access = free }}</ref><ref name = "Grabowska_2011"/> Transgenic plants expressing microbial GLDHs are improved in tolerance to herbicide, water deficit, and pathogen infections.<ref name="Lightfoot_2007">{{cite journal | vauthors =Lightfoot DA, Bernhardt K, Mungur R, Nolte S, Ameziane R, Colter A, Jones K, Iqbal MJ, Varsa E, Young B | year = 2007 | title = Improved drought tolerance of transgenic Zea mays plants that express the glutamate dehydrogenase gene (gdhA) of E. coli | journal=Euphytica | volume=156 | issue = 1–2 | pages = 103–116 | doi = 10.1007/s10681-007-9357-y| bibcode = 2007Euphy.156..103L | s2cid = 11806853 }}</ref> They are more nutritionally valuable.<ref name="isbn0-8138-1502-9">{{cite book |editor1=Wood, Andrew |editor2=Matthew A. Jenks | author = Lightfoot DA | chapter = Genes for use in improving nitrogen use efficiency in crops | title = Genes for Plant Abiotic Stress | publisher = Wiley-Blackwell | year = 2009 | pages = 167–182 | isbn = 978-0-8138-1502-2 }}</ref>

The enzyme represents a key link between [[catabolic]] and [[Anabolism|anabolic]] pathways, and is, therefore, ubiquitous in eukaryotes. In humans the relevant genes are called ''[[glutamate dehydrogenase 1|GLUD1]]'' (glutamate dehydrogenase 1) and ''[[GLUD2]]'' (glutamate dehydrogenase 2), and there are also at least five GLDH [[pseudogene]]s in the [[human genome]] as well.<ref>{{cite journal|vauthors=Aleshina YA, Aleshin VA|title= Evolutionary Changes in Primate Glutamate Dehydrogenases 1 and 2 Influence the Protein Regulation by Ligands, Targeting and Posttranslational Modifications|journal=International Journal of Molecular Sciences|volume=25|issue=8|year=2024|page= 4341|doi=10.3390/ijms25084341|article-number=4341|doi-access=free|pmid=38673928|pmc=11050691}}</ref>

==Function==
The enzyme catalyses the reversible reaction:<ref>{{KEGG enzyme|1.4.1.2}}</ref>

{{chemrxn|width=60%|
{{chemrxn/cpd|qid=Q26995161|caption=[[L-Glutamic acid]]}}
{{chemrxn/txt|+ {{chem2|NADP+}}}}
{{chemrxn/arw|direction=reversible|fwd_in={{chem2|H2O}}|fwd_out={{chem2|NH3}}|rev_in={{chem2|NH3}}|rev_out={{chem2|H2O}} }}
{{chemrxn/cpd|qid=Q306140|caption=[[α-Ketoglutaric acid|α-Ketoglutaric acid]]}}
{{chemrxn/txt|+ [[NADPH]]}}
}}

==Clinical application==

GLDH can be measured in a [[medical laboratory]] to evaluate the liver function. Elevated [[blood serum]] GLDH levels indicate liver damage and GLDH plays an important role in the differential diagnosis of liver disease, especially in combination with [[aminotransferases]].  GLDH is localised in [[mitochondria]], therefore practically none is liberated in generalised inflammatory diseases of the liver such as viral hepatitides.  Liver diseases in which necrosis of hepatocytes is the predominant event, such as toxic liver damage or hypoxic liver disease, are characterised by high serum GLDH levels.  GLDH is important for distinguishing between acute viral hepatitis and acute toxic liver necrosis or acute hypoxic liver disease, particularly in the case of liver damage with very high aminotransferases. In [[clinical trials]], GLDH can serve as a measurement for the safety of a drug.{{citation needed|date=November 2021}}

[[Enzyme immunoassay]] (EIA) for glutamate dehydrogenase (GDH) can be used as screening tool for patients with ''[[Clostridioides difficile]]'' infection. The enzyme is expressed constitutively by most strains of C.diff, and can thus be easily detected in stool. Diagnosis is generally confirmed with a follow-up EIA for C. Diff toxins A and B.{{citation needed|date=November 2021}}

==Cofactors==
[[Nicotinamide adenine dinucleotide|NAD]]<sup>+</sup> (or [[NADP]]<sup>+</sup>) is a [[Cofactor (biochemistry)|cofactor]] for the glutamate dehydrogenase reaction, producing α-ketoglutarate and [[ammonium]] as a byproduct.<ref name = "Grabowska_2011">{{cite journal | vauthors = Grabowska A, Nowicki M, Kwinta J | title = Glutamate dehydrogenase of the germinating triticale seeds: gene expression, activity distribution and kinetic characteristics | journal = Acta Physiol. Plant. | volume = 33 | doi = 10.1007/s11738-011-0801-1 | year = 2011 | issue = 5 | pages = 1981–90 | doi-access = free | bibcode = 2011AcPPl..33.1981G }}</ref><ref name="jhc.sagepub.com">{{cite journal | vauthors = Botman D, Tigchelaar W, Van Noorden CJ | title = Determination of glutamate dehydrogenase activity and its kinetics in mouse tissues using metabolic mapping (quantitative enzyme histochemistry) | journal = The Journal of Histochemistry and Cytochemistry | volume = 62 | issue = 11 | pages = 802–12 | date = November 2014 | pmid = 25124006 | doi = 10.1369/0022155414549071 | pmc=4230541}}</ref>

Based on which cofactor is used, glutamate dehydrogenase enzymes are divided into the following three classes:{{citation needed|date=November 2021}}
* EC 1.4.1.2: L-glutamate + H<sub>2</sub>O + NAD<sup>+</sup> <math>\rightleftharpoons</math> 2-oxoglutarate + NH<sub>3</sub> + NADH + H<sup>+</sup>
* EC 1.4.1.3: L-glutamate + H<sub>2</sub>O + NAD(P)<sup>+</sup> <math>\rightleftharpoons</math> 2-oxoglutarate + NH<sub>3</sub> + NAD(P)H + H<sup>+</sup>
* EC 1.4.1.4: L-glutamate + H<sub>2</sub>O + NADP<sup>+</sup> <math>\rightleftharpoons</math> 2-oxoglutarate + NH<sub>3</sub> + NADPH + H<sup>+</sup>

==Role in flow of nitrogen==
Ammonia incorporation in animals and microbes occurs through the actions of glutamate dehydrogenase and [[glutamine synthetase]]. Glutamate plays the central role in [[mammalian]] and microbe nitrogen flow, serving as both a nitrogen donor and a nitrogen acceptor.{{citation needed|date=November 2021}}

==Regulation of glutamate dehydrogenase==
In humans, the activity of glutamate dehydrogenase is controlled through [[ADP-ribose|ADP-ribosylation]], a covalent modification carried out by the gene [[sirt4]].  This regulation is relaxed in response to [[caloric restriction]] and low [[blood glucose]].  Under these circumstances, glutamate dehydrogenase activity is raised in order to increase the amount of α-ketoglutarate produced, which can be used to provide energy by being used in the [[citric acid cycle]] to ultimately produce [[adenosine triphosphate|ATP]].{{citation needed|date=November 2021}}

In microbes, the activity is controlled by the concentration of ammonium and or the like-sized rubidium ion, which binds to an allosteric site on GLDH and changes the K<sub>m</sub> ([[Michaelis constant]]) of the enzyme.<ref name="pmid6221721">{{cite journal | vauthors = Wootton JC | title = Re-assessment of ammonium-ion affinities of NADP-specific glutamate dehydrogenases. Activation of the Neurospora crassa enzyme by ammonium and rubidium ions | journal = The Biochemical Journal | volume = 209 | issue = 2 | pages = 527–31 | date = February 1983 | pmid = 6221721 | pmc = 1154121 | doi =  10.1042/bj2090527}}</ref>

The control of GLDH through ADP-ribosylation is particularly important in [[insulin]]-producing [[β cells]].  Beta cells secrete insulin in response to an increase in the ATP:[[adenosine diphosphate|ADP]] ratio, and, as amino acids are broken down by GLDH into α-ketoglutarate, this ratio rises and more insulin is secreted.  SIRT4 is necessary to regulate the metabolism of amino acids as a method of controlling insulin secretion and regulating blood [[glucose]] levels.

Bovine liver glutamate dehydrogenase was found to be regulated by nucleotides in the late 1950s and early 1960s by Carl Frieden.<ref name="pmid13654269">{{cite journal | vauthors = Frieden C | title = Glutamic dehydrogenase. II. The effect of various nucleotides on the association-dissociation and kinetic properties | journal = The Journal of Biological Chemistry | volume = 234 | issue = 4 | pages = 815–20 | date = April 1959 | doi = 10.1016/S0021-9258(18)70181-6 | pmid = 13654269 | doi-access = free }}</ref>
<ref name="pmid13895207">{{cite journal | vauthors = Frieden C | title = The unusual inhibition of glutamate dehydrogenase by guanosine di- and triphosphate | journal = Biochimica et Biophysica Acta | volume = 59 | issue = 2 | pages = 484–6 | date = May 1962 | pmid = 13895207 | doi = 10.1016/0006-3002(62)90204-4 }}</ref>
<ref>{{cite book |author= Frieden C |title= L-Glutamate Dehydrogenase, in The Enzymes, Vol VII |publisher= Academic Press |pages= 3–24|date= 1963}}</ref>
<ref name="pmid14299621">{{cite journal | vauthors = Frieden C | title = Glutamate Dehydrogenase. VI. Survey of Purine Nucleotide and Other Effects on the Enzyme from Various Sources | journal = The Journal of Biological Chemistry | volume = 240 | pages = 2028–35 | date = May 1965 | issue = 5 | doi = 10.1016/S0021-9258(18)97420-X | pmid = 14299621 | doi-access = free }}</ref>  In addition to describing the effects of nucleotides like ADP, ATP and GTP he described in detail the different kinetic behavior of NADH and NADPH. As such it was one of the earliest enzymes to show what was later described as allosteric behavior.
<ref name="MWC">{{cite journal | vauthors = Monod J, Wyman J, Changeux JP | title = On the Nature of Allosteric Transitions: A Plausible Model | journal = J Mol Biol | volume = 12 | pages = 88–118 |date=1965 | pmid = 14343300| doi = 10.1016/s0022-2836(65)80285-6}}</ref>

The activation of mammalian GDH by L-leucine and some other hydrophobic amino acids has also been long known,<ref name="YT">{{cite journal | vauthors = YIELDING KL, TOMKINS GM | title = An effect of L-leucine and other essential amino acids on the structure and activity of glutamic dehydrogenase | journal = Proc Natl Acad Sci U S A | volume = 47 | pages = 983–9 |date=1961 | issue = 7 | pmid = 13787322| doi = 10.1073/pnas.47.7.983| pmc = 221313 | bibcode = 1961PNAS...47..983L | doi-access = free }}</ref> however localization of the binding site was not clear. Only recently the new allosteric binding site for L-leucine was identified in a mammalian enzyme.<ref name="ABBB">{{cite journal | vauthors = Aleshin VA, Bunik VI, Bruch EM, Bellinzoni M | title = Structural Basis for the Binding of Allosteric Activators Leucine and ADP to Mammalian Glutamate Dehydrogenase | journal = Int J Mol Sci | volume = 23 | article-number = 11306 |date=2022 | issue = 19 | pmid = 36232607| doi = 10.3390/ijms231911306| pmc = 9570180 | doi-access = free }}</ref>

Mutations which alter the allosteric binding site of GTP cause permanent activation of glutamate dehydrogenase, and lead to [[hyperinsulinism-hyperammonemia syndrome]].

==Regulation==
[[Allosteric regulation]]:

This protein may use the [[morpheein]] model of [[allosteric regulation]].<ref name="jhc.sagepub.com"/><ref name=pmid22182754>{{cite journal | vauthors = Selwood T, Jaffe EK | title = Dynamic dissociating homo-oligomers and the control of protein function | journal = Archives of Biochemistry and Biophysics | volume = 519 | issue = 2 | pages = 131–43 | date = March 2012 | pmid = 22182754 | pmc = 3298769 | doi = 10.1016/j.abb.2011.11.020 }}</ref>

Allosteric inhibitors:
* [[Guanosine triphosphate]] (GTP)
* [[Adenosine triphosphate]] (ATP)
* [[Palmitoyl-CoA]]
* Zn<sup>2+</sup>

Activators:
* [[Adenosine diphosphate]] (ADP) <ref name="ABBB"/>
* [[Leucine]]<ref name="ABBB"/>
* [[l-isoleucine]]
* [[l-valine]]
* [[Guanosine diphosphate]]

Other Inhibitors:
* [[EGCG]]<ref>{{cite journal | vauthors = Pournourmohammadi S, Grimaldi M, Stridh MH, Lavallard V, Waagepetersen HS, Wollheim CB, Maechler P | title = Epigallocatechin-3-gallate (EGCG) activates AMPK through the inhibition of glutamate dehydrogenase in muscle and pancreatic ß-cells: A potential beneficial effect in the pre-diabetic state? | journal = The International Journal of Biochemistry & Cell Biology | volume = 88 | pages = 220–225 | date = July 2017 | pmid = 28137482 | doi = 10.1016/j.biocel.2017.01.012 | url = https://archive-ouverte.unige.ch/unige:99220 }}</ref>

Additionally, Mice GLDH shows substrate inhibition by which GLDH activity decreases at high glutamate concentrations.<ref name="jhc.sagepub.com"/>

== Isozymes ==

Humans express the following glutamate dehydrogenase [[isozyme]]s:

{|
|{{infobox protein
|Name= [[GLUD1|glutamate dehydrogenase 1]]
|caption=
|image=
|width=
|HGNCid=4335
|Symbol=[[GLUD1]]
|AltSymbols=GLUD
|EntrezGene=2746
|OMIM=138130
|RefSeq=NM_005271
|UniProt=P00367
|PDB=
|ECnumber=1.4.1.3
|Chromosome=10
|Arm=q
|Band=21.1
|LocusSupplementaryData=-24.3
}}
|{{infobox protein
|Name=[[GLUD2|glutamate dehydrogenase 2]]
|caption=
|image=
|width=
|HGNCid=4336
|Symbol=[[GLUD2]]
|AltSymbols=GLUDP1
|EntrezGene=2747
|OMIM=300144
|RefSeq=NM_012084
|UniProt=P49448
|PDB=
|ECnumber=1.4.1.3
|Chromosome=X
|Arm=q2
|Band=5
|LocusSupplementaryData=
}}
|}

== See also ==
* [[Anaplerotic reactions]]

== References ==
{{Reflist|33em}}

== External links ==
* {{MeshName|Glutamate+dehydrogenase}}

{{Mitochondrial enzymes}}
{{Citric acid cycle enzymes}}
{{Amino acid metabolism enzymes}}
{{CH-NH2 oxidoreductases}}
{{Enzymes}}
{{Glutamate metabolism and transport modulators}}
{{Portal bar|Biology|border=no}}

[[Category:EC 1.4.1]]
[[Category:Glutamate (neurotransmitter)]]