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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 ...
For example, the tripeptide glutathione is an essential part of the defenses of cells against oxidative stress. This peptide is synthesized in two steps from free amino acids. [ 134 ] In the first step, gamma-glutamylcysteine synthetase condenses cysteine and glutamate through a peptide bond formed between the side chain carboxyl of the ...
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.
Aluminium, the third most common element in the Earth's crust (after oxygen and silicon), serves no function in living cells, but is toxic in large amounts, depending on its physical and chemical forms and magnitude, duration, frequency of exposure, and how it was absorbed by the human body. [38] Transferrins can bind aluminium. [39]
The Human Cell Atlas project, which started in 2016, had as one of its goals to "catalog all cell types (for example, immune cells or brain cells) and sub-types in the human body". [13] By 2018, the Human Cell Atlas description based the project on the assumption that "our characterization of the hundreds of types and subtypes of cells in the ...
[71] [72] For example, the heparin-binding protein Azurocidin is a member of the PA clan, but with a glycine in place of the nucleophile and a serine in place of the histidine. [73] Similarly, RHBDF1 is a homolog of the S54 family rhomboid proteases with an alanine in the place of the nucleophilic serine.
Cell motility involves many receptors, crosslinking, bundling, binding, adhesion, motor and other proteins. [16] The process is divided into three steps: protrusion of the leading edge of the cell, adhesion of the leading edge and de-adhesion at the cell body and rear, and cytoskeletal contraction to pull the cell forward.
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 .