Histidine

Histidine
	Structure of histidine
Ball-and-stick model	Space-filling model
Names
	IUPAC name Histidine
	Systematic IUPAC name 2-Amino-3-(1H-imidazol-4-yl)propanoic acid
Identifiers
CAS Number	71-00-1 ;
3D model (JSmol)	Interactive image; Zwitterion: Interactive image; Protonated zwitterion: Interactive image;
Beilstein Reference	84088
ChEBI	CHEBI:15971 ;
ChEMBL	ChEMBL17962 ;
ChemSpider	6038 ;
DrugBank	DB00117 ;
ECHA InfoCard	100.000.678
EC Number	200-745-3;
Gmelin Reference	83042
IUPHAR/BPS	3310;
KEGG	D00032 ;
PubChem CID	6274;
UNII	4QD397987E ;
CompTox Dashboard (EPA)	DTXSID9023126 ;
	InChI InChI=1S/C6H9N3O2/c7-5(6(10)11)1-4-2-8-3-9-4/h2-3,5H,1,7H2,(H,8,9)(H,10,11)/t5-/m0/s1 Key: HNDVDQJCIGZPNO-YFKPBYRVSA-N ;
	SMILES O=C([C@H](CC1=CNC=N1)N)O; Zwitterion: O=C([C@H](CC1=CNC=N1)[NH3+])[O-]; Protonated zwitterion: O=C([C@H](CC1=CNC=[NH1+]1)[NH3+])[O-];
Properties
Chemical formula	C6H9N3O2
Molar mass	155.157 g·mol−1
Solubility in water	45.6mg/mL
Hazards
NFPA 704 (fire diamond)	1 1 0
Supplementary data page
	Histidine (data page)
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Histidine (symbol His or H)^[2] is an essential amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated –NH₃⁺ form under biological conditions), a carboxylic acid group (which is in the deprotonated –COO⁻ form under biological conditions), and an imidazole side chain (which is partially protonated), classifying it as a positively charged amino acid at physiological pH. Initially thought essential only for infants, it has now been shown in longer-term studies to be essential for adults also.^[3] It is encoded by the codons CAU and CAC.

Histidine was first isolated by Albrecht Kossel and Sven Gustaf Hedin in 1896.^[4] The name stems from its discovery in tissue, from ἱστός histós "tissue".^[2] It is also a precursor to histamine, a vital inflammatory agent in immune responses. The acyl radical is histidyl.

^ "Histidine (HMDB0000177)". Human Metabolome Database. Retrieved 22 March 2025.
^ ^a ^b "Nomenclature and Symbolism for Amino Acids and Peptides". IUPAC-IUB Joint Commission on Biochemical Nomenclature. 1983. Archived from the original on 9 October 2008. Retrieved 5 March 2018.
^ Kopple, Joel D; Swendseid, Marian E (1975). "Evidence that histidine is an essential amino acid in normal and chronically uremic man". Journal of Clinical Investigation. 55 (5): 881–91. doi:10.1172/JCI108016. PMC 301830. PMID 1123426.
^ Vickery, Hubert Bradford; Leavenworth, Charles S. (1928-08-01). "On the Separation of Histidine and Arginine" (PDF). Journal of Biological Chemistry. 78 (3): 627–635. doi:10.1016/S0021-9258(18)83967-9. ISSN 0021-9258.

[1] "Histidine (HMDB0000177)". Human Metabolome Database. Retrieved 22 March 2025.

[:7-2] "Nomenclature and Symbolism for Amino Acids and Peptides". IUPAC-IUB Joint Commission on Biochemical Nomenclature. 1983. Archived from the original on 9 October 2008. Retrieved 5 March 2018.

[3] Kopple, Joel D; Swendseid, Marian E (1975). "Evidence that histidine is an essential amino acid in normal and chronically uremic man". Journal of Clinical Investigation. 55 (5): 881–91. doi:10.1172/JCI108016. PMC 301830. PMID 1123426.

[4] Vickery, Hubert Bradford; Leavenworth, Charles S. (1928-08-01). "On the Separation of Histidine and Arginine" (PDF). Journal of Biological Chemistry. 78 (3): 627–635. doi:10.1016/S0021-9258(18)83967-9. ISSN 0021-9258.

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