Bleomycin-Iron Damage To Dna With Formation Of 8-Hydroxydeoxyguanosine and Base Propenals. Indications That Xanthine Oxidase Generates Superoxide From Dna Degradation Products

Bleomycin, in the presence of ferric salts, oxygen and a suitable reductant, degrades DNA with the release of base propenals, detected as thiobarbituric acid (TBA) reactivity, and the formation of 8-hydroxydeo-xyguanosine (80HdG) detected by HPLC. When xanthine oxidase is added to the incubated mixture of DNA degradation products, TBA-reactivity is destroyed but 80HdG formation is increased. EPR Spin trapping experiments show that hydroxyl radicals (OH) are formed in the reaction mixture and can be inhibited by the inclusion of either superoxide dismutase or catalase. These findings suggest that the base propenals and possibly malondialdehyde, formed from them, are aldehydic substrates for xanthine oxidase and, the product of this reaction is superoxide (O₂^-) and hydrogen peroxide (H₂O₂). Thus, TBA reactivity is destroyed in the formation of O₂^- and H₂O₂ which stimulate further oxidative damage to DNA resulting in increased 8OHdG formation.     

Inactivation of alcohol dehydrogenase by piroxicam-derived radicals

Alcohol dehydrogenase (ADH) was used as a marker molecule to clarify the mechanism of gastric mucosal damage as a side effect of using piroxicam. Piroxicam inactivated ADH during interaction of ADH with horseradish peroxidase and H₂O₂ (HRP-H₂O₂). The ADH was more easily inactivated under aerobic than anaerobic conditions, indicating participation by oxygen. Superoxide dismutase, but not hydroxyl radical scavengers, inhibited inactivation of ADH, indicating participation by superoxide. Sulfhydryl (SH) groups in ADH were lost during incubation of piroxicam with HRP-H₂O₂. Adding reduced glutathione (GSH) efficiently blocked ADH inactivation. Other SH enzymes, including creatine kinase and glyceraldehyde-3-phosphate dehydrogenase, were also inactivated by piroxicam with HRP-H₂O₂. Thus SH groups in the enzymes seem vulnerable to piroxicam activated by HRP-H₂O₂. Spectral change in piroxicam was caused by HRP-H₂O₂. ESR signals of glutathionyl radicals occurred during incubation of piroxicam with HRP-H₂O₂ in the presence of GSH. Under anaerobic conditions, glutathionyl radical formation increased. Thus piroxicam free radicals interact with GSH to produce glutathionyl radicals. Piroxicam peroxyl radicals or superoxide, or both, seem to inactivate ADH. Superoxide may be produced through interaction of peroxyl radicals with H₂O₂. Thus superoxide dismutase may inhibit inactivation of ADH through reducing piroxicam peroxyl radicals or blocking interaction of SH groups with O₂^-, or both. Other oxicam derivatives, including isoxicam, tenoxicam and meloxicam, induced ADH inactivation in the presence of HRP-H₂O₂.     

Non-oxygen-forming pathways of hydrogen peroxide degradation by bovine liver catalase at low hydrogen peroxide fluxes

Heme catalases are considered to degrade two molecules of H₂O₂ to two molecules of H₂O and one molecule of O₂ employing the catalatic cycle. We here studied the catalytic behaviour of bovine liver catalase at low fluxes of H₂O₂ (relative to catalase concentration), adjusted by H₂O₂-generating systems. At a ratio of a H₂O₂ flux (given in μM/min^- 1) to catalase concentration (given in μM) of 10 min^- 1 and above, H₂O₂ degradation occurred via the catalatic cycle. At lower ratios, however, H₂O₂ degradation proceeded with increasingly diminished production of O₂. At a ratio of 1 min^- 1, O₂ formation could no longer be observed, although the enzyme still degraded H₂O₂. These results strongly suggest that at low physiological H₂O₂ fluxes H₂O₂ is preferentially metabolised reductively to H₂O, without release of O₂. The pathways involved in the reductive metabolism of H₂O₂ are presumably those previously reported as inactivation and reactivation pathways. They start from compound I and are operative at low and high H₂O₂ fluxes but kinetically outcompete the reaction of compound I with H₂O₂ at low H₂O₂ production rates. In the absence of NADPH, the reducing equivalents for the reductive metabolism of H₂O₂ are most likely provided by the protein moiety of the enzyme. In the presence of NADPH, they are at least in part provided by the coenzyme.     

Role of reactive oxygen species in cardiac preconditioning: study with photoactivated Rose Bengal in isolated rat hearts

Oxygen radical scavengers have been shown to prevent the development of ischemic preconditioning, suggesting that reactive oxygen species (ROS) might be involved in this phenomenon. In the present study, we have investigated whether direct exposure to ROS produced by photoactivated Rose Bengal (RB) could mimic the protective effects of ischemic preconditioning.

Methods In vitro generation of ROS from photoactivated RB in a physiological buffer was first characterised by ESR spectroscopy in the presence of 2,2,6,6-tetramethyl-1-piperidone (oxoTEMP) or 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). In a second part of the study, isolated rat hearts were exposed for 2.5 min to photoactivated RB. After 5 min washout, hearts underwent 30 min no-flow normothermic ischemia followed by 30 min of reperfusion.

Results and Conclusions The production of singlet oxygen (¹O₂) by photoactivated RB in the perfusion medium was evidenced by the ESR detection of the nitroxyl radical oxoTEMPO. Histidine completely inhibited oxoTEMPO formation. In addition, the use of DMPO has indicated that (i) superoxide anions (O^·-₂) are produced directly and (ii) hydroxyl radicals (HO^·) are formed indirectly from the successive O^·-₂ dismutation and the Fenton reaction. In the perfusion experiments, myocardial post-ischemic recovery was dramatically impaired in hearts previously exposed to the ROS produced by RB photoactivation (¹O₂, O^·-₂, H₂O₂ and HO^·) as well as when ¹O₂ was removed by histidine (50 mM) addition. However, functional recovery was significantly improved when hearts were exposed to photoactivated RB in presence of superoxide dismutase (10⁵ IU/L) and catalase (10⁶ IU/L).

Further studies are now required to determine whether the cardioprotective effects of Rose Bengal in presence of O^·-₂ and H₂O₂ scavengers are due to singlet oxygen or to other species produced by Rose Bengal degradation.     

Effects of Respiratory Burst Inhibitors on Nitric Oxide Production by Human Neutrophils

Human neutrophils (PMN) activated by N-formyl-methionyl-leucyl-phenylalanine (fMLP) simultaneously release nitric oxide (.NO), superoxide anion (O₂-) and its dismutation product, hydrogen peroxide (H₂O₂). To assess whether NO production shares common steps with the activation of the NADPH oxidase, PMN were treated with inhibitors and antagonists of intracellular signaling pathways and subsequently stimulated either with fMLP or with a phorbol ester (PMA). The G-protein inhibitor, pertussis toxin (1-10 μg/ml) decreased H₂O₂ yield without significantly changing. NO production in fMLP-stimulated neutrophils; no effects were observed in PMA-activated cells. The inhibition of tyrosine kinases by genistein (1-25 μg/ml) completely abolished H₂O₂ release by fMLP-activated neutrophils; conversely, NO production increased about 1.5- and 3-fold with fMLP and PMA, respectively. Accordingly, orthovanadate, an inhibitor of phosphotyrosine phosphatase, markedly decreased -NO production and increased O_2;^- release. On the other hand, inhibition of protein kinase C with staurosporine and the use of burst antagonists like adenosine, cholera toxin or dibutyryl-cAMP diminished both H₂O₂ and NO production. The results suggest that the activation of the tyrosine kinase pathway in stimulated human neutrophils controls positively O₂^- and H₂O₂ generation and simultaneously maintains -NO production in low levels. In contrast, activation of protein kinase C is a positive modulator for O_2;^-and *NO production.     

Effect of ultrasound and ionizing radiation on a sterically hindered cyclic secondary amine: an ESR study.

The possible use of 2,2,6,6-tetramethyl-4-piperidone (TMPone) for the detection of singlet oxygen was investigated by gamma radiolysis and sonolysis of oxygen-saturated aqueous solutions. Formation of 2,2,6,6-tetra-methyl-4-piperidone-N-oxyl (TAN) was observed with both gamma radiolysis and sonolysis with a similar dependence on the concentration of TMPone up to 20 mM and a strong dependence on pH. In oxygen-saturated solutions the sonolysis of TMPone leads to the formation of the cyclic hydroxylamine (approx. 30% of the yield of TAN) while radiolysis does not. In the low pH range (5-6.5) and at high concentrations of OH radical scavengers (azide or formate), TAN is produced by sonolysis but not by radiolysis. Sonolysis of argon-saturated solutions of TMPone produces methyl radicals due to the high-temperature regions of the collapsing cavitation bubbles. The methyl radicals were detected by ESR (electron spin resonance) and spin trapping with 3,5-dibromo-2,6-dideuterio-4-nitroso-benzene sulfonate. Since the reaction of singlet oxygen with TMPone is also strongly dependent on pH, it does not seem likely that TMPone could be used for the detection of singlet oxygen in sonochemistry.     

水环境中活性氧的来源、种类及测定方法

各种环境介质和生命体中许多微观化学过程都与活性氧密切相关.本文介绍了水环境中活性氧的来源、种类和测定.它们主要包括:¹O₂(单线态氧)、O₂^-(超氧自由基)/HO₂·(氢过氧自由基)、·OH(羟基自由基)、H₂O₂、RO·(烷氧基)、ROO·(烷过氧基)和R·OH(氢过氧化物)等.其主要来源于辐射分解、热解和氧化还原法等.测定采用分子探针法、图谱法和酶法.     

Cobalt-mediated generation of reactive oxygen species and its possible mechanism

Electron spin resonance spin trapping was utilized to investigate free radical generation from cobalt (Co) mediated reactions using 5,5-dimethyl-l-pyrroline (DMPO) as a spin trap. A mixture of Co with water in the presence of DMPO generated 5,5-dimethylpyrroline-(2)-oxy(1) DMPOX, indicating the production of strong oxidants. Addition of superoxide dismutase (SOD) to the mixture produced hydroxyl radical (OH). Catalase eliminated the generation of this radical and metal chelators, such as desferoxamine, diethylenetriaminepentaacetic acid or 1,10-phenanthroline, decreased it. Addition of Fe(II) resulted in a several fold increase in the OH generation. UV and O₂ consumption measurements showed that the reaction of Co with water consumed molecular oxygen and generated Co(II). Since reaction of Co(II) with H₂O₂ did not generate any significant amount of OH radicals, a Co(I) mediated Fenton-like reaction [Co(I) + H₂O₂ → Co(II) + OH + OH⁻] seems responsible for OH generation. H₂O₂ is produced from O₂⁻ via dismutation. O₂⁻ is produced by one-electron reduction of molecular oxygen catalyzed by Co. Chelation of Co(II) by biological chelators, such as glutathione or β-ananyl-3-methyl- -histidine alters, its oxidation–reduction potential and makes Co(II) capable of generating OH via a Co(II)-mediated Fenton-like reaction [Co(II) + H₂O₂ → Co(III) + OH + OH⁻]. Thus, the reaction of Co with water, especially in the presence of biological chelators, glutathione, glycylglycylhistidine and β-ananyl-3-methyl- -histidine, is capable of generating a whole spectrum of reactive oxygen species, which may be responsible for Co-induced cell injury.     

盐及干旱胁迫对油菜抗氧化系统和RbohC、RbohF基因表达的影响

以白菜型油菜‘陇油6号’和‘天油2号’为试验材料,经MAPK抑制剂U0126、H_2O_2清除剂DMTU、NADPH氧化酶抑制剂DPI和IMD预处理后再分别进行盐胁迫、PEG-6000模拟干旱胁迫,研究其对两种油菜幼苗活性氧、抗氧化酶活性和RbohC、RbohF基因表达的影响.结果表明:盐胁迫和PEG-6000模拟干旱胁迫下,两种白菜型油菜中H_2O_2积累量上升,O_2^-·积累量下降,抗氧化酶(超氧化物歧化酶SOD、过氧化氢酶CAT、抗坏血酸过氧化物酶APX和谷胱甘肽还原酶GR)活性和RbohC、RbohF基因表达均升高.与单独胁迫处理相比,两种油菜O_2^-·积累、抗氧化酶活性和RbohC、RbohF基因的表达量均明显降低,经DMTU、DPI和IMD预处理后再分别进行盐和干旱胁迫,H_2O_2积累量下降,但U0126预处理后再进行胁迫处理,H_2O_2积累量上升.说明NADPH氧化酶、MAP激酶级联途径、H_2O_2参与了盐、干旱胁迫下活性氧产生、抗氧化酶活性变化和RbohC、RbohF基因表达的调控.     

Influence of chelators and iron ions on the production and degradation of H2O2 by beta-amyloid-copper complexes

β-Amyloid peptide (Aβ) 1–42, involved in the pathogenesis of Alzheimer’s disease, binds copper ions to form Aβ · Cu_n complexes that are able to generate H₂O₂ in the presence of a reductant and O₂. The production of H₂O₂ can be stopped with chelators. More reactive than H₂O₂ itself, hydroxyl radicals HO (generated when a reduced redox active metal complex interacts with H₂O₂) are also probably involved in the oxidative stress that creates brain damage during the disease. We report in the present work a method to monitor the effect of chelating agents on the production of hydrogen peroxide by metallo-amyloid peptides. The addition of H₂O₂ associated to a pre-incubation step between ascorbate and Aβ · Cu_n allows to study the formation of H₂O₂ but also, at the same time, its transformation by the copper complexes. Aβ · Cu_n peptides produce but do not efficiently degrade H₂O₂. The reported analytic method, associated to precipitation experiments of copper-containing amyloid peptides, allows to study the inhibition of H₂O₂ production by chelators. The action of a ligand such as EDTA is probably due to the removal of the copper ions from Aβ · Cu_n, whereas bidentate ligands such as 8-hydroxyquinolines probably act via the formation of ternary complexes with Aβ · Cu_n. The redox activity of these bidentate ligands can be modulated by the incorporation or the modification of substituents on the quinoline heterocycle.     

Trehalose: Protector of antioxidant enzymes or reactive oxygen species scavenger under heat stress?

Trehalose is known to protect membranes and macromolecules. Its accumulation has been implicated in allowing plants to tolerate stress, including heat-shock. However, under heat-shock, it is not clear whether trehalose eliminates reactive oxygen species (ROS) directly or indirectly by protecting antioxidant enzymes. In this study, we initially examined the effects of trehalose on the activities of key antioxidant enzymes, including superoxide dismutases (SODs), ascorbate catalases (CATs), and ascorbate peroxidases (APX) from wheat (Triticum aestivum L.), and then measured the ability of trehalose to scavenge hydrogen peroxide (H₂O₂) and superoxide anions (O₂⁻). Our results indicated that trehalose protected SOD activity slightly. However, it inhibited CAT and APX activities under heat stress, with a little protection of CAT activity (only about 7% promotion) at 22 °C. Moreover, trehalose scavenged H₂O₂ and O₂⁻ greatly in a concentration-dependent manner, reaching the maximal scavenging H₂O₂ rate of 95% and O₂⁻ rate of 78%, respectively, at 50 mM trehalose. These results suggest that trehalose plays a direct role in eliminating H₂O₂ and O₂⁻ in wheat under heat stress.     

盐及干旱胁迫对油菜抗氧化系统和RbohC、RbohF基因表达的影响

以白菜型油菜‘陇油6号’和‘天油2号’为试验材料,经MAPK抑制剂U0126、H₂O₂清除剂DMTU、NADPH氧化酶抑制剂DPI和IMD预处理后再分别进行盐胁迫、PEG-6000模拟干旱胁迫,研究其对两种油菜幼苗活性氧、抗氧化酶活性和RbohC、RbohF基因表达的影响.结果表明: 盐胁迫和PEG-6000模拟干旱胁迫下,两种白菜型油菜中H₂O₂积累量上升,O₂^-·积累量下降,抗氧化酶(超氧化物歧化酶SOD、过氧化氢酶CAT、抗坏血酸过氧化物酶APX和谷胱甘肽还原酶GR)活性和RbohC、RbohF基因表达均升高.与单独胁迫处理相比,两种油菜O₂^-·积累、抗氧化酶活性和RbohC、RbohF基因的表达量均明显降低,经DMTU、DPI和IMD预处理后再分别进行盐和干旱胁迫,H₂O₂积累量下降,但U0126预处理后再进行胁迫处理,H₂O₂积累量上升.说明NADPH氧化酶、MAP激酶级联途径、H₂O₂参与了盐、干旱胁迫下活性氧产生、抗氧化酶活性变化和RbohC、RbohF基因表达的调控.     

Inactivation of myocardial dihydrolipoamide dehydrogenase by myeloperoxidase systems: effect of halides, nitrite and thiol compounds

Dihydrolipoamide dehydrogenase (LADH) lipoamide reductase activity decreased whereas enzyme diaphorase activity increased after LADH treatment with myeloperoxidase (MPO) dependent systems (MPO/H₂O₂/halide, MPO/NADH/halide and MPO/H₂O₂/nitrite systems. LADH inactivation was a function of the composition of the inactivating system and the incubation time. Chloride, iodide, bromide, and the thiocyanate anions were effective complements of the MPO/H₂O₂ system. NaOCl inactivated LADH, thus supporting hypochlorous acid (HOCl) as putative agent of the MPO/H₂O₂/NaCl system. NaOCl and the MPO/H₂O₂/NaCl system oxidized LADH thiols and NaOCl also oxidized LADH methionine and tyrosine residues. LADH inactivation by the MPO/ NADH/halide systems was prevented by catalase and enhanced by superoxide dismutase, in close agreement with H₂O₂ production by the LADH/NADH system. Similar effects were obtained with lactoperoxidase and horseradish peroxidase suplemented systems. L-cysteine, N-acetylcysteine, penicillamine, N-(2-mercaptopropionylglycine), Captopril and taurine protected LADH against MPO systems and NaOCl. The effect of the MPO/H₂O₂/NaNO₂ system was prevented by MPO inhibitors (sodium azide, isoniazid, salicylhydroxamic acid) and also by L-cysteine, L-methionine, L-tryptophan, L-tyrosine, L-histidine and reduced glutathione. The summarized observations support the hypothesis that peroxidase-generated “reactive species” oxidize essential thiol groups at LADH catalytic site.     

A convenient electrochemical preparation of reduced methyl viologen and a kinetic study of the reaction with oxygen using an anaerobic stopped-flow apparatus

1. Single reduced methyl viologen (MV^.+) acts as an electron donor in a number of enzyme systems. The large changes in extinction coefficient upon oxidation (λ_max 600 nm; MV^.+, = 1.3 · 10⁴ M⁻¹ · cm⁻¹; oxidised form of methyl viologen (MV²⁺), = 0.0) make it ideally suited to kinetic studies of electron transfer reactions using stopped-flow and standard spectrophotometric techniques.

2. A convenient electrochemical preparation of large amounts of MV^.+ has been developed.

3. A commercial stopped-flow apparatus was modified in order to obtain a high degree of anaerobicity.

4. The reaction of MV^.+ with O₂ produced H₂O₂ (k > 5 · 10⁶ M⁻¹ · s⁻¹, pH 7.5, 25 °C). H₂O₂ subsequently reacted with excess MV^.+ (k = 2.3 · 10³ M⁻¹ · s⁻¹, pH 7.5, 25 °C) to produce water. The kinetics of this reaction were complex and have only been interpreted over a limited range of concentrations.

5. The results support the theory that the herbicidal action of methyl viologen (Paraquat, Gramoxone) is due to H₂O₂ (or radicals derived from H₂O₂) induced damage of plant cell membrane.     

Enhanced Superoxide Production with on Change of the Antioxidant Activity in Gingival Fluid of Patients with Chronic Adult Periodontitis

In the gingival crevicular fluid (GCF) of control and chronic adult periodontitis (CAP) patients there is a spontaneous release of O₂^- radicals from polymorphonuclear leukocytes (PMN). The addition of the exogenous stimuli phorbol myrystate acetate (PMA) decreased the O₂^- formation in control GCF, while in CAP patients produced a marked enhancement of O₂^- generation.

The circulating PMN of control subjects did not show a spontaneous O₂^- formation, differently from CAP patients. On the contrary, a similar O₂^- production was measured when the circulating PMN were stimulated with PMA.

Moreover, the antioxidant activity measured in 10μl of cell free gingival supernatant (GS) of control and CAP patients had the same values by inhibiting 12.6% and 18.9% respectively of the O₂^- formation supported by a xanthine/xanthine oxidase system.

Probably, the protective or destructive effect of PMN in GCF of CAP patients depends on the variations of the rate of O₂^- formation in respect to the intrinsic antioxidant property of GS.     

The effect of iron and agar on production of hydrogen peroxide by stimulated and activated mouse peritoneal macrophages

The effect of iron on H₂O₂ production by mouse peritoneal macrophages exposed to opsonised zymosan has been investigated. Macrophages elicited with thioglycollate broth produced less H₂O₂ than macrophages activated by Corynebacterium parvum, and levels were not affected by prior incubation of the cells with 0.1 mM iron nitrilotriacetate. However, preincubation with the iron chelator desferrioxamine (1 mM) reduced H₂O₂ production by both types of macrophages. Incubation of macrophages with agar, a component of thioglycollate broth, also reduced H₂O₂ production, particularly by C. parvum-activated macrophages. The results indicate that although iron appears to be necessary for H₂O₂ production by macrophages, the low level of production by thioglycollate-elicited macrophages is not due to an inadequate level of metabolically utilisable iron, but may be a result of prior ingestion of agar present in the broth.     

Free radical scavenging actions of metallothionein isoforms I and II

By employing electron spin resonance spectroscopy, we examined the free radicals scavenging effects of hepatic metallothionein (MT) isoforms I and II (MTs-I and II) on four types of free radicals. Solutions of 0.15mM of MT-I and 0.3mM of MT-II were found to scavenge the 1,1-diphenyl-2-picrylhydrazyl radicals (1.30 × 10¹⁵ spins/ml) completely. In addition, both isoforms exhibited total scavenging action against the hydroxyl radicals (1.75 × 10¹⁵ spins/ml) generated in a Fenton reaction. Similarly, 0.3mM of MT-I scavenged almost 90% of the superoxide (2.22 × 10¹⁵ spins/ml) generated by the hypoxanthine and xanthine oxidase system, while a 0.3mM MT-II solution could only scavenge 40% of it. By using 2,2,6,6-tetramethyl-4-piperidone as a “spin-trap” for the reactive oxygen species (containing singlet oxygen, superoxide and hydroxyl radicals) generated by photosensitized oxidation of riboflavin and measuring the relative signal intensities of the resulting stable nitroxide adduct, 2,2,6,6-tetramethyl-4-piperidine-1-oxyl, we observed that MT-II (0.3 mM) could scavenge 92%, while MT-I at 0.15 mM μl/ml concentrations could completely scavenge all the reactive species (2.15 × 10¹⁵ spins/ml) generated.

The results of these studies suggest that although both isoforms of MT are able to scavenge free radicals, the MT-I appears to be a superior scavenger of superoxide and 1,1 diphenyl-2-picrylhydrazyl radicals.     

Formation of Hydroxyl Radicals in Biological Systems. Does Myoglobin Stimulate Hydroxyl Radical Formation from Hydrogen Peroxide?

Incubation of horse-heart oxymyoglobin or metmyoglobin with excess H₂O₂ causes formation of myoglobin(IV), followed by haem degradation. At the time when haem degradation is observed, hydroxyl radicals (.OH) can be detected in the reaction mixture by their ability to degrade the sugar deoxyribose. Detection of hydroxyl radicals can be decreased by transferrin or by OH scavengers (mannitol, arginine, phenylalanine) but not by urea. Neither transferrin nor any of these scavengers inhibit the haem degradation. It is concluded that intact oxymyoglobin or metmyoglobin molecules do not react with H₂O₂ to form OH detectable by deoxyribose, but that H₂O₂ eventually leads to release of iron ions from the proteins. These released iron ions can react to form OH outside the protein or close to its surface. Salicylate and the iron chelator desferrioxamine stabilize myoglobin and prevent haem degradation. The biological importance of OH generated using iron ions released from myoglobin by H₂O₂ is discussed in relation to myocardial reoxygenation injury.     

茉莉酸甲酯对木豆不定根染料木素含量及抗氧化系统影响

为探讨茉莉酸甲酯(Methyl Jasmonate,MJ)对木豆不定根影响,研究了茉莉酸甲酯的不同浓度及处理时间对木豆不定根中染料木素的含量及抗氧化系统的影响。研究结果表明,诱导子的浓度和处理时间对不定根中染料木素的含量有重要影响。在MJ浓度为100μmol·L^-1,处理时间为48 h时,染料木素的含量最高,为1.38 mg·g^-1,是对照组的4.03倍。在此基础上,研究了100μmol·L^-1的MJ处理对木豆不定根抗氧化系统的影响,结果表明,MJ处理的木豆不定根明显发生了氧化胁迫,O_2^-速率、H_2O_2和MDA含量明显升高,同时不定根中SOD和POD活性明显升高,但是抗氧化酶活性的提高并未消除不定根的氧化胁迫,这种氧化胁迫导致了木豆不定根次生代谢产物合成能力提高。     

Activation of the anticancer drug CCNU into a free radical intermediate via UV irradiation--an ESR study

We studied the formation of a free radical induced by UV irradiation of 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) in benzene. It was determined a stable nitroxide radical by ESR spectroscopy. We confirmed that sterically hindered cyclic amine 2,2,6,6-tetramethyl-4-piperidone (TMPone) was transformed into a corresponding stable free nitroxyl radical during UV irradiation. When CCNU was present, the rate of free radical formation from TMPone increased considerably.