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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 protonated), classifying it as a ...
Chemical formula: C 6 H 9 N 3 O 2 Molar mass: 155.16 g·mol −1 Systematic name: 2-amino-3-(3H-imidazol-4-yl)propanoic acid Abbreviations: H, His Synonyms: Imidazole alanine ({S/D})-α-amino-1H-imidazole-4-propanoic acid 4-(2-amino-2-carboxyethyl)imidazole α-amino-1H-imidazole-4-propionic acid α-amino-4-imidazolepropionic acid Anti-rheuma C00768
There are several splice variants of H 3 present in various species. Though all of the receptors are 7-transmembrane g protein coupled receptors, H 1 and H 2 are quite different from H 3 and H 4 in their activities. H 1 causes an increase in PIP 2 hydrolysis, H2 stimulates gastric acid secretion, and H3 mediates feedback inhibition of histamine.
The H 1 receptor is a histamine receptor belonging to the family of rhodopsin-like G-protein-coupled receptors. This receptor is activated by the biogenic amine histamine . It is expressed in smooth muscles , on vascular endothelial cells , in the heart, and in the central nervous system .
These motifs include the H, N, G1, F, and G2 boxes. [8] The autophosphorylation H-box is contained in the N-terminal dimerization and histidine phosphotransfer (DHp) domain. In HK853-CD, crystallized from Thermotoga maritima, this domain is a helical-hairpin and is formed by residues 232-317. The histidine phosphorylation site is located at His ...
The endothelial protease vasohibin [f] uses a cysteine as the nucleophile, but a serine to coordinate the histidine base. [43] [44] Despite the serine being a poor acid, it is still effective in orienting the histidine in the catalytic triad. [43] Some homologues alternatively have a threonine instead of serine at the acid location. [43]
A histamine agonist is a drug which causes increased activity at one or more of the four histamine receptor subtypes.. H 1 agonists promote wakefulness. [1]H 2: Betazole and Impromidine are examples of agonists used in diagnostics to increase histamine.
H 1 antagonists, also called H 1 blockers, are a class of medications that block the action of histamine at the H 1 receptor, helping to relieve allergic reactions. Agents where the main therapeutic effect is mediated by negative modulation of histamine receptors are termed antihistamines ; other agents may have antihistaminergic action but are ...