Histidine

Histidine (symbol His or H) 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. It is encoded by the codons CAU and CAC.

l-Histidine

Skeletal formula of histidine (zwitterionic form)
Names
IUPAC name
Histidine
Other names
2-Amino-3-(1H-imidazol-4-yl)propanoic acid
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.000.678
KEGG
UNII
  • 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 Y
    Key: HNDVDQJCIGZPNO-YFKPBYRVSA-N Y
  • 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
C6H9N3O2
Molar mass 155.157 g·mol−1
4.19g/100g @ 25 °C
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 was first isolated by Albrecht Kossel and Sven Gustaf Hedin in 1896. It is also a precursor to histamine, a vital inflammatory agent in immune responses. The acyl radical is histidyl.

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