L-Histidine

L-Histidine is one of the twenty proteinogenic amino acids and is dietarily indispensable for humans. What sets it apart from the other protein amino acids is its side chain: an unfused imidazole ring whose ring nitrogen has a pKa close to neutral, so histidine is the only common amino acid that buffers meaningfully at physiological pH. The same ring makes it a strong chelator of transition-metal ions, which is why histidine residues sit in the active sites of a large number of metalloenzymes and why immobilised-metal affinity chromatography works on histidine tags. In the body it is the direct precursor of the dipeptides carnosine and anserine and a building block of haemoglobin. Industrial L-histidine is produced by submerged fermentation with Corynebacterium glutamicum — several production strains have been formally assessed by EFSA for feed use — which makes the material non-animal in origin and suitable for vegan, vegetarian and non-animal-derived-component declarations. Two forms are traded: the free base (CAS 71-00-1, C6H9N3O2, MW 155.15) and L-histidine monohydrochloride monohydrate (CAS 5934-29-2), which is more soluble and is often preferred for liquid systems and feed premixes. The free base carries USP, Ph. Eur., JP and FCC monographs; USP requires 98.5–101.5% assay on the dried basis, specific rotation +12.6° to +14.0° measured at 110 mg/mL in 6 N hydrochloric acid, loss on drying not more than 0.2%, residue on ignition not more than 0.4% and pH 7.0–8.5 in a 1-in-50 solution. Thovek exports pharmacopoeial and food-grade L-histidine to supplement brands, parenteral and enteral nutrition manufacturers, biologics formulators using histidine buffer systems, and cell culture media houses. Each lot ships with a full certificate of analysis, residual solvent and elemental impurity data, TSE/BSE-free and allergen-free statements, and Kosher and Halal certification where the buyer requires it. Cell-culture-suitable and low-endotoxin cuts can be arranged against a firm specification.