Hydroxyl radical histidine

Fig. 3. a) First order plot of oxygen uptake in the Methylene-blue (MB)-sensitized photooxidation of GA 8.4 pM and 1.3 mM histidine (control) in phosphate buffer pH 7. b) Percentage radical scavenging activity for the control molecule Trolox and GA at pH 7.4 in phosphate buffer 10 mM (hydroxyl radical) and pH 10 in sodium carbonate buffer 50 mM (anion superoxide radical). 

Nonspecific cytochrome P450-mediated oxidation involves enzyme-catalyzed formation of reactive oxygen species (superoxide anions and hydroxyl radicals), which oxidize susceptible amino acids such as proline, arginine, lysine, and histidine. 

Hydroxyl radical reacts very quickly with most organic substances, including free amino acids and amino acid residues in proteins. These reactions are diffusion-controlled and their rate constants are very high (Table 5). Hydroxyl radical reacts with low specificity with all amino acid residues, although tryptophan, tyrosine, histidine, and cysteine are particularly vulnerable. 

Singlet Oxygen Scavengers and/or Quenchers — /3-carotene, a-tocopherol. histidine, tryptophan, guanine, uric acid Hydroxyl Radical Scavengers — most organic compounds k 8 10 M- s- ... 

M.A. Babizhayev et al., L-camosine (P-alanyl-L-histidine) and carcinine (P-alanyl-histamine) act as natural antioxidants with hydroxyl-radical-scavenging and lipid-peroxidase activities. Biochem. J., 304(1994) 509-516. 

The amino acid histidine is used as a bulking agent for lyophilization and can additionally serve as a buffer (histidine/histidine hydrochloride) and stabilizer in the formulation (Nema et al., 2002). Histidine is a rather efficient quencher of singlet oxygen and a scavenger of hydroxyl radicals (Halliwell and Gutteridge, 1985). Thus, the presence of histidine in the parenteral formulation can be very important for the photochemical stability of the product. 

Food products contain less copper than iron copper is mainly bound to protein as in ceruloplasmin. Copper ions are also chelated by albumin in mammalian and avian skeletal muscles and brain, they are chelated by camosine, anserine, and other histidine dipeptides. Cu + ions are more reactive than Fe ions and decompose hydrogen peroxide to produce hydroxyl radicals at a rate over 50 times higher than Fe + (Decker, 2001). However, the mechanism of the prooxidative effects of copper is most likely a mechanism other than that for iron, which is the reason why prevention of that catalysis in food systems requires a different strategy (Hultin, 1994). 

Reaction of Neurospora PPO with uniformly labeled phenol, under conditions similar to those used by Wood and Ingraham (1965), led to covalent incorporation of < 0.03 mol labeled phenol/mol PPO (Pfiffner et al., 1981). The enzyme lost its activity during the reaction there was also a loss of one mol of histidine and one mol of copper per mol of Neurospora PPO. Brooks and Dawson (1966) had shown earlier that k inactivation of mushroom PPO was accompanied by loss of copper from the enzyme. Lerch (1978) proposed that inactivation of Neurospora PPO may have occurred as a result of the oxidation of histidine due to formation of singlet oxygen or hydroxyl radicals during the reaction. However, Kahn et al. (1982) could not detect superoxide ion (Oj) or hydroxyl radical (0H ) formation during the reaction of mushroom PPO with substrates. 

Hydroxyl radicals are extremely reactive chemical species that can initiate lipid peroxidation in LDL (Bedwell et al., 1989). Therefore, ascorbic acid should promote, rather than prevent, metal ion-dependent oxidative modification of LDL. In a partial explanation of the paradoxical protection of LDL by ascorbic acid against metal ion-dependent oxidation, we have observed that ascorbic acid oxidation products (i.e., dehydroascorbic acid) effectively prevent LDL oxidation by heme and H2O2 or by Cu (Retsky et al., 1993 Retsky and Frei, 1995). Although the mechanism underlying this observation remains to be elucidated, it is likely that histidine residues on LDL apo B are converted to 2-oxo-histidine in the presence of Cu2+ and ascorbic acid (Uchida and Kawakishi, 1990) or dehydroascorbic acid... 

Inoue S, Kawanishi S (1989) ESR evidence for superoxide, hydroxyl radicals and singlet oxygen produced from hydrogen peroxide and nickel(II) complex of glycylglycyl-L-histidine. Biochem Biophys Res Commum 159 445-451 Inoue S, Yamamoto K, Kawanishi S (1990) DNA damage induced by metabolites of o-phenylphenol in the presence of copper(II) ion. Chem Res Toxicol 3 144-149... 

In vivo, these compounds demonstrated the ability to markedly reduce metastasis of MDA-MB-435 xenografts in nude rnice. A different mechanism of antitumor activity has been proposed for D-fructose-L-histidine. FruHis stands out of other naturally occurring D-fructose-amino acids in respect of its exceptional metal-binding and antioxidant activities. Remarkably, FruHis completely protected DNA degradative oxidation by copper-promoted hydroxyl radicals in vitro, while none of other tested major antioxidants from tomato (ascorbic acid, quercetin, caffeic acid etc.) could match the protective potential of FruHis. Even more... 

A number of a-aryl-A-alkyl nitrones and contrast enhancement compositions, which can be used to make contrast enhancement layer photoresist composites (230, 231), and inhibitors of free radical polymerization of monomers in nonexposed regions of the photoresist layer at selective actinic radiation (232). Histidine was used as a catalyst in the synthesis of a, A-diaryl nitrones in situ (233). To study diphenylborate chelates with mono- and bidentate ligands, a series of hydroxyl-containing nitrones have been synthesized (Fig. 2.7) (234-237). 

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