Editing Glutamic acid (section)

== Chemistry ==
===Ionization===
[[File:Glutamic Acid at physiological pH V2.svg|class=skin-invert-image|thumb|left|The glutamate monoanion.]]
When glutamic acid is dissolved in water, the [[amine|amino group]] (−{{chem|N|H|2}}) may gain a [[proton]] ({{chem|H|+}}), and/or the [[carboxylic acid|carboxyl groups]] may lose protons, depending on the [[pH|acidity]] of the medium.

In sufficiently acidic environments, both carboxyl groups are protonated and the molecule becomes a [[cation]] with a single positive charge, HOOC−CH({{chem|N|H|3|+}})−({{chem|C|H|2}})<sub>2</sub>−COOH.<ref name=neub>{{cite journal|pmc=1263308 |date=1936 |last1=Neuberger |first1=A. |title=Dissociation constants and structures of glutamic acid and its esters |journal=Biochemical Journal |volume=30 |issue=11 |pages=2085–2094 |doi=10.1042/bj0302085 |pmid=16746266 }}</ref>

At [[pH]] values between about 2.5 and 4.1,<ref name=neub/> the carboxylic acid closer to the amine generally loses a proton, and the acid becomes the neutral zwitterion <sup>−</sup>OOC−CH({{chem|N|H|3|+}})−({{chem|C|H|2}})<sub>2</sub>−COOH. This is also the form of the compound in the crystalline solid state.<ref name=roda>{{cite journal | last1 = Rodante | first1 = F. | last2 = Marrosu | first2 = G. | year = 1989 | title = Thermodynamics of the second proton dissociation processes of nine α-amino-acids and the third ionization processes of glutamic acid, aspartic acid and tyrosine | journal = Thermochimica Acta | volume = 141 | pages = 297–303 | doi = 10.1016/0040-6031(89)87065-0 | bibcode = 1989TcAc..141..297R }}</ref><ref name=cryst>{{cite journal | last1 = Lehmann | first1 = Mogens S. | last2 = Koetzle | first2 = Thomas F. | last3 = Hamilton | first3 = Walter C. | year = 1972 | title = Precision neutron diffraction structure determination of protein and nucleic acid components. VIII: the crystal and molecular structure of the β-form of the amino acidl-glutamic acid | journal = Journal of Crystal and Molecular Structure | volume = 2 | issue = 5| pages = 225–233 | doi = 10.1007/BF01246639 | bibcode = 1972JCCry...2..225L | s2cid = 93590487 }}</ref>  The change in protonation state is gradual; the two forms are in equal concentrations at pH 2.10.<ref name=ionpH/>

At even higher pH, the other carboxylic acid group loses its proton and the acid exists almost entirely as the glutamate anion <sup>−</sup>OOC−CH({{chem|N|H|3|+}})−({{chem|C|H|2}})<sub>2</sub>−COO<sup>−</sup>, with a single negative charge overall. The change in protonation state occurs at pH 4.07.<ref name=ionpH/> This form with both carboxylates lacking protons is dominant in the [[physiological pH]] range (7.35–7.45).

At even higher pH, the amino group loses the extra proton, and the prevalent species is the doubly-negative anion <sup>−</sup>OOC−CH({{chem|N|H|2}})−({{chem|C|H|2}})<sub>2</sub>−COO<sup>−</sup>. The change in protonation state occurs at pH 9.47.<ref name=ionpH>William H. Brown and Lawrence S. Brown (2008), ''Organic Chemistry'' (5th edition). Cengage Learning. p. 1041. {{ISBN|0495388572|978-0495388579}}.</ref>

===Optical isomerism===
Glutamic acid is [[chiral]]; two mirror-image [[Enantiomer|enantiomers]] exist: {{sm|d}}(−), and {{sm|l}}(+). The {{sm|l}} form is more widely occurring in nature, but the {{sm|d}} form occurs in some special contexts, such as the [[bacterial capsule]] and [[cell wall]]s of the [[bacteria]] (which produce it from the {{sm|l}} form with the [[enzyme]] [[glutamate racemase]]) and the [[liver]] of [[mammals]].<ref name=Dglut>National Center for Biotechnology Information, "[https://pubchem.ncbi.nlm.nih.gov/compound/23327 D-glutamate]". ''PubChem Compound Database'', CID=23327. Accessed 2017-02-17.</ref><ref name=DgEcoli>{{cite journal | last1 = Liu | first1 = L. | last2 = Yoshimura | first2 = T. | last3 = Endo | first3 = K. | last4 = Kishimoto | first4 = K. | last5 = Fuchikami | first5 = Y. | last6 = Manning | first6 = J. M. | last7 = Esaki | first7 = N. | last8 = Soda | first8 = K. | year = 1998 | title = Compensation for {{sc|D}}-glutamate auxotrophy of ''Escherichia coli'' WM335 by {{sc|D}}-amino acid aminotransferase gene and regulation of ''murI'' expression | journal = Bioscience, Biotechnology, and Biochemistry | volume = 62 | issue = 1 | pages = 193–195 | doi = 10.1271/bbb.62.193 | pmid = 9501533 | doi-access = free }}</ref>
<!-- ref name=Dglut
{{sm|d}}-glutamate is also present in certain foods e.g., soybeans and also arises from the turnover of the intestinal tract microflora, whose cell walls contain significant {{sm|d}}-glutamate. Unlike other {{sm|d}}-amino acids, {{sm|d}}-glutamate is not oxidized by the {{sm|d}}-amino acid oxidases, and therefore this detoxification pathway is not available for handling {{sm|d}}-glutamate. Likewise, {{sm|d}}-glutamic acid, when ingested, largely escapes most deamination reactions (unlike the {{sm|l}}-counterpart). Free {{sm|d}}-glutamate is found in mammalian tissue at surprisingly high levels, with {{sm|d}}-glutamate accounting for 9% of the total glutamate present in liver. {{sm|d}}-glutamate is the most potent natural inhibitor of glutathione synthesis identified to date and this may account for its localization to the liver, since circulating {{sm|d}}-glutamate may alter redox stability ({{cite journal | pmid = 11158923 | volume=280 | title=Regulatory responses to an oral D-glutamate load: formation of D-pyrrolidone carboxylic acid in humans | year=2001 | journal=Am J Physiol Endocrinol Metab | pages=E214-20  | last1 = Raj | first1 = D | last2 = Langford | first2 = M | last3 = Krueger | first3 = S | last4 = Shelton | first4 = M | last5 = Welbourne | first5 = T | doi = 10.1152/ajpendo.2001.280.2.e214}}). Certain eels are known to use {{sm|d}}-glutamic acid as a pheromone for chemical communication.-->