page_title: Histidine
section_title: Ligand
hierarchical_section_title: Histidine / Properties of the imidazole side chain / Ligand
caption_attribution_description: Cu3 site in the enzyme laccase
context_page_description: Histidine is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group, a carboxylic acid group, and an imidazole side chain, 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.
  Histidine was first isolated by German physician 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.
context_section_description: The imidazole sidechain of histidine commonly serves as a ligand in metalloproteins. One example is the axial base attached to Fe in myoglobin and hemoglobin.
caption: The tricopper site found in many laccases, notice that each copper center is bound to the imidazole sidechains of histidine (color code: copper is brown, nitrogen is blue).
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