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The histidine amino acid is a precursor for histamine, an amine produced in the body necessary for inflammation. [25] The enzyme histidine ammonia-lyase converts histidine into ammonia and urocanic acid. A deficiency in this enzyme is present in the rare metabolic disorder histidinemia, producing urocanic aciduria as a key diagnostic finding.
The enzyme histidine decarboxylase (EC 4.1.1.22, HDC) is transcribed on chromosome 15, region q21.1-21.2, and catalyzes the decarboxylation of histidine to form histamine. In mammals, histamine is an important biogenic amine with regulatory roles in neurotransmission , gastric acid secretion and immune response .
Histamine is derived from the decarboxylation of the amino acid histidine, a reaction catalyzed by the enzyme L-histidine decarboxylase. It is a hydrophilic vasoactive amine. Conversion of histidine to histamine by histidine decarboxylase
The triad of cytomegalovirus protease [b] uses histidine as both the acid and base triad members. Removing the acid histidine results in only a 10-fold activity loss (compared to >10,000-fold when aspartate is removed from chymotrypsin). This triad has been interpreted as a possible way of generating a less active enzyme to control cleavage ...
Cystine and Histidine are very commonly involved, since they both have a pKa close to neutral pH and can therefore both accept and donate protons. Many reaction mechanisms involving acid/base catalysis assume a substantially altered pKa. This alteration of pKa is possible through the local environment of the residue [citation needed].
Imidazole is the side chain of histidine and is typically used at a concentration of 150 - 500 mM for elution. Histidine or histamine can also be used. Decrease in pH; When the pH decreases, the histidine residue is protonated and can no longer coordinate the metal tag, allowing the protein to be eluted.
The reverse reaction of phosphorylation is called dephosphorylation, and is catalyzed by protein phosphatases. Protein kinases and phosphatases work independently and in a balance to regulate the function of proteins. [3] The amino acids most commonly phosphorylated are serine, threonine, tyrosine, and histidine.
Histidine ammonia-lyase is a cytosolic enzyme catalyzing the first reaction in histidine catabolism, the nonoxidative deamination of L-histidine to trans-urocanic acid. [5] The reaction is catalyzed by 3,5-dihydro-5-methyldiene-4 H -imidazol-4-one (MIO), an electrophilic cofactor which is formed autocatalytically by cyclization of the protein ...