Histidine-tyrosine

Besides all the sensory and texturizing properties, GA has interesting antioxidant properties such as an efficient capacity for deactivation of excited electronic states and moderated radical scavenging capacity. There is increasing experimental evidence that associate the antioxidant function with its protein fraction, mainly by amino acid residues such as histidine, tyrosine and lysine, which are generally considered as antioxidants molecules (Marcuse, 1960,1962 Park et al., 2005). 

Aromatic amine-containing haptens are converted to diazonium salts with ice-cold nitrous acid. Diazonium salts can then react with a protein at alkaline pH (around 9) through electrophilic attack of the diazonium salt at histidine, tyrosine and(or) tryptophan residues of the carrier protein (Table 7). 

Many recent studies have focused on the mechanisms of formaldehyde modification, cross-linking, and reversal.19,37 8 In general, these studies found that formaldehyde is very specific, particularly when reaction times are relatively short. The amino-termini, lysine, tryptophan, and cysteine are the targets of modification in this case. Longer reaction times reveal more extensive modifications, including arginine, histidine, tyrosine, and phenylalanine. 

Chemical Reviews paper. We can only discuss a small number of these here, but some important categories are (1) synthetic Fe(II)-Cu(I) complexes and their reactions with O2, (2) oxidized heme-copper models (Fe(III)-X-Cu(II) complexes, where X equals 0x0- and hydroxo-bridged complexes, cyanide-bridged complexes, or other X-bridged complexes), (3) crosslinked histidine-tyrosine residues at the heme-copper center, and (4) Cua site synthetic models. 

Although the iron centers are coordinated by polar groups (aspartate, glutamate, histidine, tyrosinate, and thiolate side chains), the overall environment created by residues surrounding the iron-ligand center often has a hydrophobic character. Amino acids located in this second... 

If spots of multiple labeled amino acids (e.g., lysine, cysteine, histidine, tyrosine) are found, check whether the intensity of the multiple labeled derivatives is in the same order as the mono-labeled derivative. Only in that case could the determined amino acid be N-terminal. 

The Pauly reagent will react with histidine, tyrosine, thyroxine, and dihydroxyphenylalanine to give a bright yellow and red color. Diiodotyrosine and creatinine give much weaker reactions. 

In 1970s, first application of metal-chelate affinity chromatography which is later named as "immobilized-metal (ion) affinity chromatography (IMAC) was perfomed. Metal-chelate chromatography technique exploits selective interactions and affinity between transition metal immobilized on a solid support (resin) via a metal chelator and amino acid residues which act as electron donors in the protein of interest [25-26]. As well as aromatic and heterocyclic compounds, proteins such as histidine, tyrosine, tyriptophane and phenylalanine posses affinity to transition metals which form complexes with compounds rich in electrons [25,27]. 

In summary, protein molecules may contain up to nine amino acids that are readily derivatizable at their side chains aspartic acid, glutamic acid, lysine, arginine, cysteine, histidine, tyrosine, methionine, and tryptophan. These nine residues contain eight principal functional groups with sufficient reactivity for modification reactions primary amines, carboxylates, sulfhydryls (or disulfides), thioethers, imidazolyls, gua-nidinyl groups, and phenolic and indolyl rings. All of these side chain functional groups in addition to the N-terminal a-amino and the C-terminal a-carboxylate form the full complement of polypeptide reactivity within proteins (Fig. 12). 

How can a simple cofactor, such as heme, give rise to a wide spectrum of protein functionalities While the Fe(III)/Fe(II) couple has a standard redox potential of 0.77 V, when complexed with a protoporphyrin to form free heme, it may decrease to —0.115 V [3-5]. When heme is introduced into a protein matrix, redox potential shows an impressive variation of around 1 V. The electrochemical data for structurally characterized heme proteins involved in electron transfer and redox catalysis has been compiled at the Heme Protein Database (HPD, http //heme.chem. columbia.edu/heme) [6]. The database comprises not only peroxidases but also catalases, oxidases, monooxygenases, and cytochromes. From b-type heme with histidine-tyrosine ligation (E° = 0.55 V) to c-type heme with histidine-methionine... 

The fact that the four metal ligands provided by the transferrin apoprotein involve three different amino acid residues, i.e., histidine, tyrosine, and aspartate, is most interesting. Inorganic mononuclear complexes with such a variety of ligand types are not often encountered however, a Mn(III) complex with imidazole, carboxylate-, and phenoxide-type ligation has been structurally characterized. The complex [Mn(sal)2(ImH)2] (Fig. 7) (sal = salicylate) possesses two trans imidazoles and two salicylates disposed trans to one another (142). 

Buse, G., Soulimane,T., Dewor, M., Meyer, H. E., and Bfggel, M., 1999, Evidence for a copper-coordinated histidine-tyrosine cross-link in the active site of cytochrome oxidase, Prot. 

There is agreement that the enzyme contains nonheme iron at the active site with N or O ligands (probably histidine, tyrosine, and/or aspartate residnes), bnt there is less certainty as to the oxidation state, coordination sphere, and... 

Much of Landsteiner s pioneer work was carried out with haptens that were aromatic amines. The compounds were converted to diazonium salts with nitrous acid and aUowed to react with proteins at alkaline pH (approximately 9). Reaction occurred primarily with histidine, tyrosine, and tryptophan residues of the protein carrier. For a representative procedure, see Kabat (p. 799 seq.). An interesting application of this procedure was the preparation of a chloramphenicol-protein conjugate which was used to elicit antibodies specific for chloramphenicol. In this case, a prior reduction of the nitro group of chloramphenicol to an amino group was required. As early as 1937, carcinogenic compounds were conjugated to protein carriers by means of their isocyanate derivatives which were prepared from amines. Immune sera were raised, and their properties were studied. - ... 

Vanadium(IV) complexes with two dipeptides glycyl-tyrosine and glycyl-phenylalanine (Gly-Tyr and Gly-Phe, respectively) and their oxovanadium(lV) and (V) complexes have been observed.382, 01 The complex formed with Gly-Tyr showed coordination by the peptide backbone moieties, and no interaction from the distal phenolic hydroxy group.601 A histidine-tyrosine derivatized peptide was shown to complex Viv in a pentadentate manner (120).564 The adduct between VlV and a model of the active-site peptide of protein tyrosine phosphatases has been spectroscopically characterized.602 Similar characterization of in serum suggests that protein complexes form, and that both Viv and Vv can exist as complexes with transferrin and albumin.603 ESEEM has been used to characterize the complexes of apoferritin with V02+ and suggests that the carboxylates, one water molecule, and one histidine ligand fill the coordination sites of the vanadium.604... 

Use of this method enabled synthesis of the histidine-tyrosine sidechain-coupled... 

There is agreement that the enzyme contains nonheme iron at the active site with N or O ligands (probably histidine, tyrosine, and/or asptartate residues),32,33 but less certainty as to the oxidation state, coordination sphere, and mode of O2 binding and activation for the iron center. Earlier in this chapter the activation of O2 by FeR(DPAH)2 for the transformation of pyrocatechol to muconic acid is discussed (Table 6-2 and Scheme 6-1). Because this parallels the chemistry of the... 

In addition to the stereospecilicity, NAD(P)H-linked dehydrogenases that convert > CHOH to > C=0 differ in the apparatus that has evolved to catalyse proton transfer from substrate oxygen. That apparatus can centre round a zinc ion or an acid-base histidine, tyrosine or lysine. 

Morris and Hall (35) have examined a series of carbohydrates. Larger molecules are, of course, feasible. Chan and Markley (36) have assigned histidine, tyrosine and phenylalanine protonated carbon resonances in uniformly enriched (20%) oxidized ferro-dixin by heteronuclear H/C 2D shift correlation NMR. Polypeptide resonances have also been assigned using C/H 2D NMR (3J7,3f3). In these systems H/H homonu-clear, H/C heteronuclear and N/H heteronuclear 2D techniques have allowed direct confirmation of assignments and connectivities, in particular the NH nitrogens and protons. 

Type 2 copper centers are not uniform in ligand or ligand stereochemistries. One common feature is, however, that in the active enzyme, one coordination site is always free to bind oxygen. The most common ligand in type 2 copper centers is histidine. Tyrosine (often modified), methionine, and cysteine occur as well. There are three histidines and a modified tyrosine in amine oxidase and lysyl oxidase [28]. In diamine oxidase, two of the histidine residues have probably been replaced by cysteines [29]. In galactose oxidase, the copper ion is coordinated by two tyrosines, two histidines and an acetate ion [30]. Dopamine-/J-hydroxylase contains two differently coordinated copper ions per functional unit. One is coordinated by three histidines and a methionine and the other by two histidines and another, yet unknown, ligand [ 31 ]. Last but not least, the type 2 copper ion in Cu,Zn-superoxide dismutase is coordinated by four histidine residues, one of which connects the copper ion to the zinc ion, the second metal ion in the active site of the enzyme [32,33] (Fig. 6). 

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