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Imidazole is incorporated into many important biological compounds. The most pervasive is the amino acid histidine, which has an imidazole side-chain. Histidine is present in many proteins and enzymes, e.g. by binding metal cofactors, as seen in hemoglobin. Imidazole-based histidine compounds play an important role in intracellular buffering. [17]
Histidine ball and stick model spinning. 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 –NH 3 + 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 ...
In nature, imidazole alkaloids are found both as secondary plant compounds and as byproducts of histidine metabolism in marine organisms. One well-known imidazole alkaloid is pilocarpine , which is present in the leaves of Paraguay jaborandi .
Histamine base, obtained as a mineral oil mull, melts at 83–84 °C. [8] Hydrochloride [9] and phosphorus [10] salts form white hygroscopic crystals and are easily dissolved in water or ethanol, but not in ether. In aqueous solution, the imidazole ring of histamine exists in two tautomeric forms, identified by which of the two nitrogen atoms ...
Ergothioneine is a thiourea derivative of the betaine of histidine and contains a sulfur atom bonded to the 2-position of the imidazole ring. [19] Typical of thioureas, ergothioneine is less reactive than typical thiols such as glutathione towards alkylating agents like maleimides.
Aromatic amino acids often serve as the precursors to important biochemicals. Histidine is the precursor to histamine.; Tryptophan is the precursor to 5-hydroxytryptophan and then serotonin, tryptamine, auxin, kynurenines, and melatonin.
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English: Top row: L-Histidine, D-Histidine and DL (or RS)-Histidine. Bottom row: same but with the alternative 3H tautomer in the imidazole ring. Bottom row: same but with the alternative 3H tautomer in the imidazole ring.