Reactions of desferrioxamine with peroxynitrite-derived carbonate and nitrogen dioxide radicals

The iron chelating agent desferrioxamine inhibits peroxynitrite-mediated oxidations and attenuates nitric oxide and oxygen radical-dependent oxidative damage both in vitro and in vivo. The mechanism of protection is independent of iron chelation and has remained elusive over the past decade. Herein, stopped-flow studies revealed that desferrioxamine does not react directly with peroxynitrite. However, addition of peroxynitrite to desferrioxamine in both the absence and the presence of physiological concentrations of CO2 and under excess nitrite led to the formation of a one-electron oxidation product, the desferrioxamine nitroxide radical, consistent with desferrioxamine reacting with the peroxynitrite-derived species carbonate (CO3*-) and nitrogen dioxide (*NO2) radicals. Desferrioxamine inhibited peroxynitrite-dependent free radical-mediated processes, including tyrosine dimerization and nitration, oxyhemoglobin oxidation in the presence of CO2, and peroxynitrite plus carbonate-dependent chemiluminescence. The direct two-electron oxidation of glutathione by peroxynitrite was unaffected by desferrioxamine. The reactions of desferrioxamine with CO3*- and *NO2 were unambiguously confirmed by pulse radiolysis studies, which yielded second-order rate constants of 1.7 x 10(9) and 7.6 x 10(6) M(-1) s(-1), respectively. Desferrioxamine also reacts with tyrosyl radicals with k = 6.3 x 10(6) M(-1) s(-1). However, radical/radical combination reactions between tyrosyl radicals or of tyrosyl radical with *NO2 outcompete the reaction with desferrioxamine and computer-assisted simulations indicate that the inhibition of tyrosine oxidation can be fully explained by scavenging of the peroxynitrite-derived radicals. The results shown herein provide an alternative mechanism to account for some of the biochemical and pharmacological actions of desferrioxamine via reactions with CO3*- and *NO2 radicals.     

Reactions of 4 methylphenyl isocyanate with amino acids

Arylisocyanates are important intermediates in the chemical industry. Amongst the main damage after low levels of isocyanate exposure are lung sensitization and asthma. Protein adducts of isocyanates might be involved in the aetiology of sensitization reactions. Blood protein adducts are used as dosimeters for modifications of macromolecules in the target organs where the disease develops. To develop methods for the quantitation of protein adducts we reacted 4 methylphenyl isocyanate 4MPI with the tripeptide valyl glycyl glycine and with single amino acids yielding N 4 methylphenyl carbamoyl L valyl glycyl glycine 4MPI Val Gly Gly, N 4 methylphenyl carbamoyl L valine 4MPI Val, N 4 methylphenyl carbamoyl L aspartic acid 4MPI Asp, N acetyl S 4 methylphenyl carbamoyl L cysteine 4MPI AcCys, N acetyl N 4 methylphenyl carbamoyl lysine 4MPI AcLys, N acetyl O 4 methylphenyl carbamoyl tyrosine 4MPI AcTyr and N acetyl O 4 methylphenyl carbamoyl D,L serine 4MPI AcSer. The hydrolysis of the adducts was tested under acidic and basic conditions, to obtain the maximum yield of 4 methylaniline 4MA. The isocyanates were hydrolysed for 1 h, 3h and 24h at 100 C with 6 M HCl in and or 0.1 M NaOH at room temperature, following methods applied for the analyses of biological samples of arylisocyanate exposed workers. In addition, we applied a new protocol: the adducts were hydrolyzed for 1-24 h in 0.3 M NaOH at 100 C. The hydrolysates were analysed using HPLC with UV detection and quantified against the internal standard, 4 fluoroaniline or 4 chloroaniline. 4MA was obtained with the best yields using 0.3M NaOH; after 24 h all amino acid adducts were cleaved under these conditions. Acid hydrolysis of 4MPI Val and 4MPI Asp yielded the respective hydantoins 3 4 methylphenyl 5 isopropyl 1,3 imidazoline 2,4 dione and 2 1 4 methylphenyl 2,5 dioxoperhydro 4 imidazolyl acetic acid. For future studies, we propose to hydrolyse biological samples with 0.3 M NaOH at 100 C to release the maximum amount of 4MA from the adducts. However, in biological samples from workers, hydrolysable adducts can also result from arylamine exposure. Therefore, we propose to analyse the N terminal adducts of isocyanates with blood protein to distinguish between arylamine and arylisocyanate exposure.     

Changes in concentraions of free radicals and amino acids in developing maize inflorescences and fruits

The changes in the concentration of free radicals and bound amino acids in developing maize inflorescences and fruits were ascertained. The concentration rises markedly when tissues disintegrate and desiccate. A slight increase in the concentration may be ascribed to the rise of metabolic processes connected with kernel formation.     

Reaction of azide radicals with amino acids and proteins.

The azide radical N3 reacts selectively with amino acids, in neutral solution preferentially with tryptophan (k (N3 + TrpH) = 4.1 X 10(9) dm3 mol(-1s-1) and in alkaline solution also with cysteine and tyrosine (k(N3 + CyS-) = 2.7 X 10(9) dm3 mol-1s-1) and k(N3 + TyrO-) equals 03.6 X 10(9) dm3 mol-1s-1). Oxidation of the enzyme yADH by N3 involves primary attacks, mainly at tryptophan residues, and subsequent slow secondary reactions. N3-induced inactivation of yADH is likely to occur upon oxidation of tryptophan residues in the substrate binding pocket (58-TrpH and 93-TrpH) since the substrate ethanol although unreactive with N3, protects yADH and since elADH, which does not contain tryptophan in the substrate pocket, is comparatively resistant against N3-attack. N3 exhibits low reactivity with nucleic acid derivatives and it is inert towards aliphatic compounds such as methanol and sodium dodecylsulphate.     

Effect of proteins and amino acids on oxidation of liposomes by hydroxyl and peroxyl free radicals

The ability of proteins to protect model liposome membranes from oxidation by hydroxyl and peroxyl free radicals was investigated.     

Dielectric properties,free radicals,amino acids,and some elements in maize tissues

Data on (1) permitivity and dielectric losses, (2) free radical concentrations, and (3) potassium, sodium, magnesium, calcium, nitrogen, and amino acid contents in tissues of nodal roots, internodes, and leaves of maize plant are presented in the paper. The participation of these factors in the transport phenomenon and the degree of their cooperation in the transport process are discussed.     

Specific occurrence of selenium in enzymes and amino acid tRNAs

In contrast to the widespread ability of bacteria, plants, and animals to incorporate selenium nonspecifically into proteins in the form of selenomethionine residues, the selenoamino acid selenocysteine occurs as a highly specific component of a few selenium-dependent enzymes. Selenocysteine has been identified in glycine reductase, formate dehydrogenase, and hydrogenase of bacterial origin and glutathione peroxidase from mammalian and avian sources. In these enzymes there is evidence that the selenol group, which is largely ionized at physiological pH, functions as a redox center. It now seems clear, from studies with both prokaryotes and eukaryotes, that the UGA opal stop codon is used to specify the cotranslational insertion of selenocysteine into proteins. The factors that allow this unusual use of the stop codon are, however, unknown. The occurrence of selenium as a normal constituent of several bacterial tRNA species has been established. The presence of a selenonucleoside, 5-methylaminomethyl-2-selenouridine, in the first or wobble position of the anticodons of certain glutamate and lysine iso-acceptor species influences codon-anticodon interaction and thus may serve to regulate translational processes. The biosynthesis of the selenonucleoside appears to involve the ATP-dependent activation of the sulfur in a preformed 5-methylaminomethyl-2-thiouridine residue in tRNA and replacement of the sulfur with selenium.     

埃他卡林对低氧性肺动脉高压患者某些血清酶活性及自由基代谢的影响

目的:研究埃他卡林对低氧性肺动脉高压(HPH)患者血中心肌酶活性与自由基代谢的影响,为埃他卡林临床治疗HPH的作用机制提供依据。方法:在海拔5 000m以上高原,将110名HPH患者随机分为埃他卡林治疗组(试验组,n=74)和安慰剂对照组(n=36),治疗前、治疗6个月后分别采血检测丙氨酸氨基转移酶(ALT)、门冬氨酸氨基转移酶(AST)、γ-谷氨酰转肽酶(γ-GT)、肌酸激酶(CK)、乳酸脱氢酶(LDH)、丙二醛(MDA)、一氧化氮(NO)的含量及超氧化物歧化酶(SOD)、一氧化氮合酶(NOS)的活性。结果:服药前试验组较对照组ALT、AST、γ-GT、CK、LDH、MDA、NO、SOD、NOS的活性无统计学差异(P0.05);服药6个月后试验组较对照组ALT[(56.70±9.87)vs(65.90±10.40)]、AST[(56.30±11.40)vs(66.47±9.73)]、γ-GT[(66.53±8.96)vs(74.97±6.51)]、CK[(200.90±25.38)vs(222.60±30.21)]、LDH[(285.85±25.97)vs(309.92±38.18)]、MDA含量均降低,SOD[(71.09±8.78)vs(64.18±7.28)]、NO[(57.70±12.80)vs(48.10±7.99)]含量增高,NOS[(40.24±6.64)vs(34.40±7.01)]活性增高,MDA[(6.74±1.64)vs(8.67±1.77)]含量降低,差异有统计学意义(P0.05)。结论:氧自由基参与了HPH的发生发展过程,埃他卡林减轻脂质过氧化反应,并对低氧造成应激损伤的心肌细胞具有明显的保护作用。     

Transformation of free radicals of gamma-irradiated enzymes during long-term storage

The ESR method was used to study free radical processes occurring in gamma-irradiated enzymes upon their long-term storage (up to 4 years) both at room temperature and at 4 degrees C. Simultaneously, studied was the biological activity of gamma-irradiated enzymes subjected to a long-term storage. The immobilization of enzymes on dialdehyde cellulose or polycaproamine was shown to preserve their biological activity during the postirradiation storage.     

Oxygen free radicals induced release of lysosomal enzymes in vitro

Summary The effect of oxygen free radicals, generated by xanthine and xanthine oxidase, was studied on the release of lysosomal hydrolase from rat liver lysosomes in vitro. A lysosomal enriched subcellular fraction was prepared, using differential centrifugation technique, from the homogenate of rat liver. The biochemical purity of the lysosomal fraction was established by using the markers of different cellular organelles. Oxygen free radicals were generated in vitro by the addition of xanthine and xanthine oxidase. The release of lysosomal hydrolase (-glucuronidase) from the lysosomal fraction was measured. There was a 3 to 4 fold increase in the release of -glucuronidase activity in the presence of xanthine and xanthine oxidase when compared to that in the absence of xanthine and xanthine oxidase. In the presence of superoxide dismutase (SOD), a scavenger of oxygen free radicals, the xanthine and xanthine oxidase system was unable to induce the release of -glucuronidase activity from the lysosomes. Sonication (2 bursts for 15 sec each) and Lubrol (2 mg/10 mg lysosomal protein) treatment, which are known to cause membrane disruption, also induced the release of -glucuronidase from lysosomal fraction. This release of -glucuronidase by sonication and lubrol treatment was not prevented by SOD. These data indicate that lysosomal disruption is a consequence of oxygen free radicals, generated by xanthine and xanthine oxidase.Abbreviations HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - EGTA Ethylene Glycol Bis-(-aminoethyl ether)N,N,-N,N-tetracetic acid - Tris Tris (hydroxymethyl) aminomethane - SOD Superoxide Dismutase     

Reactions of partially purified tyrosine phenol lyase with threonine and other amino acids

Both enantiomers of threonine are transformed to α-ketobutyrate with a partially purified preparation of tyrosine phenol lyase from the cells of Escherichia intermedia A-21. Allothreonine does not undergo the same reaction but is, instead, converted to glycine. The action of tyrosine phenol lyase on a number of other α-amino acids was also studied. The inversion of configuration at C-2 due to the exchange of the α-proton is not a general phenomenon. The mechanism of action of tyrosine phenol lyase on d-amino acids is discussed.