The hypobromous acid (HOBr, HBrO) is an inorganic acid produced by the oxidation of the bromide anion (Br-). The addition of bromine to water gives hydrobromic acid (HBr) and hypobromous acid (HOBr) through a disproportionation reaction. Br2 + H2O = HOBr + HBr
Hypobromous acid is a very weak acid, somewhat unstable, existing as a dilute solution at room temperature. It is produced in warm-blooded vertebrate organisms (including humans), by the action of the enzyme eosinophil peroxidase.
The discovery that hypobromous acid can regulate the activity of collagen IV has attracted a great deal of attention..
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Bromine is ubiquitous in animals as ionic bromide (Br-), but its essential function was unknown until recently..
Recent research has shown that bromine is essential for basement membrane architecture and tissue development.
The enzyme peroxidain uses HOBr to cross-link sulfilimine, which is cross-linked in the collagen IV scaffolds of the basement membrane..
Hypobromous acid is produced in warm-blooded vertebrate organisms by the action of the enzyme eosinophil peroxidase (EPO).
EPO generates HOBr from H2O2 and Br- in the presence of a plasma concentration of Cl-.
Myeloperoxidase (MPO), from monocytes and neutrophils, generates hypochlorous acid (HOCl) from H2O2 and Cl-.
EPO and MPO play an important role in host defense mechanisms against pathogens, using HOBr and HOCl respectively.
The MPO / H2O2 / Cl- system in the presence of Br- also generates HOBr by the reaction of the HOCl formed with Br-. More than a powerful oxidant, HOBr is a powerful electrophile.
The plasma concentration of Br- is more than 1000 times lower than that of the chloride anion (Cl-). Consequently, endogenous production of HOBr is also lower compared to HOCl.
However, HOBr is significantly more reactive than HOCl when the oxidability of the compounds studied is not relevant, so the reactivity of HOBr could be more associated with its electrophilic strength than with its oxidizing power (Ximenes, Morgon & de Souza, 2015).
Although its redox potential is lower than that of HOCl, HOBr reacts with amino acids faster than HOCl.
The halogenation of tyrosine ring by HOBr is 5000 times faster than that of HOCl.
HOBr also reacts with nucleoside nucleobases and DNA.
2'-deoxycytidine, adenine and guanine, generate 5-bromo-2'-deoxycytidine, 8-bromoadenine and 8-bromoguanine in EPO / H2O2 / Br- and MPO / H2O2 / Cl- / Br- systems (Suzuki, Kitabatake and Koide, 2016).
McCall, et al. (2014) have shown that Br is a required cofactor for the formation of sulfilimine cross-links catalyzed by the enzyme peroxidasine, a post-translational modification essential for the architecture of collagen IV of the basement membranes and the development of tissues..
Basement membranes are specialized extracellular matrices that are key mediators of signal transduction and mechanical support of epithelial cells..
Basement membranes define the architecture of epithelial tissue and facilitate tissue repair after injury, among other functions..
Embedded within the basement membrane is a collagen IV scaffold crosslinked with sulfilimine, which gives the matrix functionality in the multicellular tissues of all animals..
Collagen IV scaffolds provide mechanical strength, serve as a ligand for integrins and other cell surface receptors, and interact with growth factors to establish signaling gradients..
Sulfilimine (sulfimide) is a chemical compound that contains a sulfur to nitrogen double bond. Sulfilimine bonds stabilize collagen IV strands found in the extracellular matrix.
These bonds covalently link the methionine 93 (Met93) and hydroxylysine 211 (Hyl211) residues of adjacent polypeptide strands to form a larger collagen trimer..
Peroxidase forms hypobromous acid (HOBr) and hypochlorous acid (HOCl) from bromide and chloride, respectively, which can mediate the formation of sulfilimine crosslinks..
The bromide, converted to hypobromous acid, forms an intermediate of the bromosulfonium ion (S-Br) that participates in the formation of cross-links.
McCall, et al. (2014) demonstrated that dietary Br deficiency is lethal in the Drosophila fly, while Br replacement restores its viability.
They also established that bromine is an essential trace element for all animals due to its role in the formation of sulfilimine bonds and collagen IV, which is of vital importance for the formation of basement membranes and the development of tissues..
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