Histidine is amino acid that was discovered back in 1896 by Albrecht Kossel and Sven Hedin - simultaneously but independently. The first researcher obtained Histidine by precipitation with mercuric chloride from the alkaline solution which contained the products of hydrolysis of the protamine – sturine. The second one isolated Histidine from the precipitate obtained by the base fraction from hydrolyzed protein being treated with silver nitrate and later with ammonia till the moment when a maximum precipitation occurred.

Chemical Structure
Structure of Histidine

IUPAC Name: (2S)-2-Amino-3-(3H-imidazol-4-yl)propanoic acid
Symbol: Three-letter code - His. One-letter code - H
Molecular Weight (Molar Mass): 155.15456 g/mol
Molecular Formula (Structural Formula): C6H9N3O2
Canonical SMILES: C1=C(NC=N1)CC(C(=O)O)N
Isomeric SMILES: C1=C(NC=N1)C[C@@H](C(=O)O)N
CAS Number: 71-00-1
MDL Number: MFCD00064315
Melting point: 285 °C
Solubility in water: 41.6 g/1 L (25 °C); pKa - 1,82; pKb - 9,17
2D Molfile: Get the molfile
3D PDB file: Get the PDB file
Other names: (S)-4-(2-Amino-2-carboxyethyl)imidazole ; (S)-alpha-Amino-1H-imidazole-4-propanoic acid; L-2-Amino-3-(4-imidazolyl)propionic acid; (2S)-2-azaniumyl-3-(3H-imidazol-4-yl)propanoate

Histidine is usually referred to as a semi-essential amino acid, as adults are normally able to produce an adequate amount of it. However, children may not. This amino acid is also known for being a precursor of histamine - a compound that is generally released by the immune system cells in an allergic reaction.

Today Histidine is widely recognized as an essential amino acid which cannot be formed by other nutrients, and therefore should be in the diet to let your body obtain it. Your body mostly needs Histidine to regulate and to utilize essential trace elements like iron, copper, molybdenum, zinc, and manganese. This amino acid is also essential in forming numerous metal-bearing enzymes and compounds, such as the antioxidant super oxide dismutase.

Meanwhile, many toxic metals like mercury, lead, and cadmium, along with threatening excess of essential minerals like zinc and copper, usually stimulate the rapid formation of metallothionein inside the cells of your brain, liver, and kidneys to protect these cells. Metallothionein needs Histidine to be formed, so people without a Histidine diet whose body is contaminated with heavy metals are subject to the body's depletion of adequate stores of this amino acid, thus causing mineral-enzyme deficiencies and dysregulations. This body condition is best recognized by dysfunction of Histidine-dependent compounds, coupled with low blood plasma concentration of it.

By the way, if you do not tolerate sulfur-bearing food, such as broccoli and garlic, and show the elevated blood plasma L-cysteine levels, it means that you suffer from inactivation of Histidine and of iron-dependent enzyme cysteine dioxygenase.