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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 ...
Four of the heme centers are bis-histidine ligated and presumably serve to shuttle electrons to the active site. The active site heme, however, is uniquely ligated by a single lysine residue. This enzyme belongs to the family of oxidoreductases, specifically those acting on other nitrogenous compounds as donors with a cytochrome as acceptor.
In more rare cases, a missense mutation in the genetic code of the T-protein, causing the histidine in position 42 to be mutated to arginine, was also found to result in nonketotic hypergycinemia. This specific mutation directly affected the active site of the T-protein, causing lowered efficiency of the glycine cleavage system.
1.2 Recruited reaction steps of the citric acid cycle and malate aspartate shuttle 1.3 Reaction steps from malate to pyruvate and lactate 2 Intracellular compartmentalization of the glutaminolytic pathway
Steap family proteins are defined by a shared transmembrane domain that in Steap3 has been shown to function as a transmembrane electron shuttle, moving cytoplasmic electrons derived from NADPH across the lipid bilayer to the extracellular face where they are used to reduce Fe 3+ to Fe 2+ and potentially Cu 2+ to Cu 1+. [6]
In orthodox two-component signaling, a histidine kinase protein autophosphorylates on a histidine residue in response to an extracellular signal, and the phosphoryl group is subsequently transferred to an aspartate residue on the receiver domain of a response regulator. In phosphorelays, the "hybrid" histidine kinase contains an internal ...
This histidine residue becomes phosphorylated during the succinate forming step in the reaction mechanism. The exact binding location of succinate is not well-defined. [ 9 ] The formation of the nucleotide triphosphate occurs in an ATP grasp domain, which is located near the N-terminus of the each β subunit.
The molecular mechanism behind this effect is the steric organization of the globin chain; a histidine residue, located adjacent to the heme group, becomes positively charged under acidic conditions (which are caused by dissolved CO 2 in working muscles, etc.), releasing oxygen from the heme group. [15]