Histidine acids

The imidazole ring of histidine acid-base properties... 

The active sites of these enzymes can have a nitrogen ligand, usually as histidine (acid phosphatases and some protein phosphatases), a nucleophilic serine residue (alkaline phosphatases), a cysteine residue in which the thiol group can form a covalent species with the phosphate ester (protein phosphatases), or an aspartate-linked phosphate (plasma membrane ion pumps). The inhibitory form of vanadium is usually anionic vanadate V(V), but cationic vanadyl V(IV) has also shown strong inhibition of some types of phosphorylase reactions. Above neutral pH, speciation of vanadyl ions produces anionic V(IV) species capable of inhibition of enzymes in the traditional transition-state analogue manner [5],... 

The glucose-l-phosphatase from E. coli hydrolyzes phytate as well as glucose-1-phosphate. This enzyme is a member of the histidine acid phosphatase family (Lee et al., 2003). Glucose-l-phosphatase cleaves only the 3-phosphate from phytate, and no further hydrolysis takes place. It is the only phosphatase... 

As stated earlier, lipases act at the interface between hydrophobic and hydrophilic regions, a characteristic that distinguishes lipases from esterases. Similar to serine proteases, lipases share the nucleophile-histidine-acidic residue catalytic triad that manifests itself as either a Ser-His-Asp triad or a Ser-His-Glu triad. The enzyme s catalytic site often is buried within the protein structure, surrounded by relatively hydrophobic residues. An a-helical polypeptide structure acts as a cover, making the site inaccessible to solvents and substrates. For the lipase to be active, the a-helical lid structure has to open so that the active site is accessible to the substrate. The phenomenon of interfacial activation is often associated with reorientation of the lid, increasing the hydrophobicity of the surface in the vicinity of the active site and exposing it. The opening of the lid structure may be initiated on interaction with an oiFwater interface. 

The enzymatic process is remarkably efficient due to the close proximity of the serine nucleophile and the histidine acid/base catalyst. As a result, enzymatic hydrolysis by cholinesterase is one hundred million times faster than chemical hydrolysis. The process is so efficient that acetylcholine is hydrolysed within a hundred microseconds of reaching the enzyme. 

Blood Hemoglobin histidine Acid hydrolysis of globin, derivatization Positive ion electrospray Not reported Black et al. (1997b)... 

Fig. 3 Schematic representation of a typical mechanism for a histidine acid phosphatase enzyme. Based on Lindqvist et al. [4]...

In addition, the crystal structure of the histidine acid phosphatase from the pathogen Francisella tularensis tHAP) has been solved showing that the three-dimensional structure is similar to that of prostatic acid phosphatase [8]. Moreover, a mutation of the Asp261 (the equivalent to Asp258 in prostatic acid phosphatase) traps the substrate 3 -AMP (3 -adenosine monophosphate) which provides supporting evidence to the importance of this residue in the catalytic mechanism [8]. 

Singh H, Felts RL, Schuermarm JP et al (2009) Crystal Structures of the histidine acid phosphatase from Francisella tularensis provide insight into substrate recognition. J Mol Biol 394 893-904... 

Two classes of enzymes that degrade myoinositol hexakisphosphate are recognized 3-phytase (EC 3.1.3.8) initially cleaves the phosphate at the 3-position on the myoinositol ring, leaving myo-inositol 1,2,4,5,6 pentakisphosphate (this phytase belongs to the family of histidine acid phosphatases Mitchell et al, 1997), whereas 6-phytase (EC 3.1.3.26) preferentially initiates dephosphorylation at the 6-position, leaving myoinositol 1,2,3,4,5 pentakisphosphate. 

Initial efforts by Noort et al. (1996, 1997) to detect the protein adducts of sulfur mustard focused on the 4-(2-hydroxyethylthioethyl)-L-aspartate, 5-(2-hydroxye-thylthioethyl)-L-glutamate, cysteine and N-terminal valine adduct, and two histidine adducts, Nl- and N3-(2-hydroxyethylthioethyl)-L-histidine. Acidic hydrolysis and pronase digestion were used to release these adducts from globin. Pronase is a mixture of proteinases isolated from the extracellular fluid of Streptomyces gri-seus. Adducts were derivatized with 9-fluorenylmethyl chloroformate, followed by identification and quantification, using GC-MS. 

CfiHqNaO . M.p. 277 C. The naturally occurring substance is laevorotatory. Histidine is one of the basic amino-acids occurring in the hydrolysis products of proteins, and particularly of the basic proteins, the protamines and histones. It is an essential constituent of the food of animals. 

Fig. 10.12 Sequence alignment of trypsin, chymotrypsin and thrombin (bovine). The active sites histidine, aspartic acid and serine are highlighted.

Supplement 1955 3634-3793 Sulphonic acids Indigo-disulphonic acid (indigocarmine), 304. Amines, 308. Keto-ammes Pyramidone, 452. Allan-toin, 474. Murexide, 499. Amino-carboxylic acids Histidine, 513. j Hydrazines, 531. Azo compounds, 535. 1... 

Able to form Ag salt of lower solubility than AgQ in H2O. Therefore applications in photographic processes Inhibition of histidine decarboxylase activity Antifoggant for color films Anthelmintic activity Quenching for oil composition caialj si for the industrial isomerization of cis a, (3 unsaturaied carboxylic acids rubber vul-cankzate improver... 

An imidazole ring is a structural unit m the ammo acid histidine (Section 27 1) and is involved m a large number of biological processes as a base and as a nucleophile... 

Some ammo acids have side chains that bear acidic or basic groups As Table 27 3 indicates these ammo acids are characterized by three values The third pK reflects the nature of the side chain Acidic ammo acids (aspartic and glutamic acid) have acidic side chains basic ammo acids (lysine arginine and histidine) have basic side chains The isoelectric points of the ammo acids m Table 27 3 are midway between the pK values of the zwitterion and its conjugate acid Take two examples aspartic acid and lysine Aspartic acid has an acidic side chain and a pi of 2 77 Lysine has a basic side chain and a pi of 9 74... 

Among the biochemical reactions that ammo acids undergo is decarboxylation to amines Decarboxylation of histidine for example gives histamine a powerful vasodila tor normally present m tissue and formed m excessive amounts under conditions of trau matic shock... 

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