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1.
Donald M. Hunten 《Journal of molecular evolution》1979,14(1-3):71-78
Summary Photolysis of H2O in the atmosphere near the surface is a copious source of OH, HO2, and probably superoxides, some of which are likely to condense on the surface and migrate through the pores. The processes have been modeled in detail for their atmospheric interest. The models successfully account for the rarity of CO and O2, the notable variability of ozone, and the escape flux of hydrogen. Though only qualitative estimates can be made of surface deposition rates and lifetimes, the suggested amounts are in the range inferred by Viking. The OH rapidly destroys any organic molecules that are present as vapors.Analogous reactions involving adsorbed water have been studied by Huguenin. These processes can be driven by the much larger photon fluxes at longer ultraviolet wavelengths. The suggested explanations, and many of the experiments, make it likely that peroxides, superoxides, and adsorbed OH are all present. Both kinds of process, and their combinations, seem in principle able to explain the absence of all organic molecules and the variety of observed oxidants. Since they operate planetwide, there is a strong suggestion that the observed conditions are typical. Oases of higher than average humidity may in fact be even more hostile than the average region, because water under Martian surface conditions is anything but benign.Laboratory simulation of the atmospheric processes must pay careful attention to scaling.Curiously, similar OH densities occur at the Earth's surface, The notable differences are food for thought, and ideas about the origin of life may be particularly affected.Based on an invited paper at the Second International Colloquium on Mars, Pasadena, January 15–18, 1979 相似文献
2.
Manganese porphyrin reduces renal injury and mitochondrial damage during ischemia/reperfusion 总被引:2,自引:2,他引:0
Saba H Batinic-Haberle I Munusamy S Mitchell T Lichti C Megyesi J MacMillan-Crow LA 《Free radical biology & medicine》2007,42(10):1571-1578
Renal ischemia/reperfusion (I/R) injury often occurs as a result of vascular surgery, organ procurement, or transplantation. We previously showed that renal I/R results in ATP depletion, oxidant production, and manganese superoxide dismutase (MnSOD) inactivation. There have been several reports that overexpression of MnSOD protects tissues/organs from I/R-related damage, thus a loss of MnSOD activity during I/R likely contributes to tissue injury. The present study examined the therapeutic benefit of a catalytic antioxidant, Mn(III) meso-tetrakis(N-n-hexylpyridinium-2-yl)porphyrin (MnTnHex-2-PyP(5+)), using the rat renal I/R model. This was the first study to examine the effects of MnTnHex-2-PyP(5+) in an animal model of oxidative stress injury. Our results showed that porphyrin pretreatment of rats for 24 h protected against ATP depletion, MnSOD inactivation, nitrotyrosine formation, and renal dysfunction. The dose (50 microg/kg) used in this study is lower than doses of various types of antioxidants commonly used in animal models of oxidative stress injuries. In addition, using novel proteomic techniques, we identified the ATP synthase-beta subunit as a key protein induced by MnTnHex-2-PyP(5+) treatment alone and complex V (ATP synthase) as a target of injury during renal I/R. These results showed that MnTnHex-2-PyP(5+) protected against renal I/R injury via induction of key mitochondrial proteins that may be capable of blunting oxidative injury. 相似文献
3.
Rahman I 《Mutation research》2005,579(1-2):58-80
5.
Basab Bijayi Dhar 《Inorganica chimica acta》2009,362(1):185-188
Titanium(II) solutions, prepared by dissolving titanium metal in triflic acid+HF, react readily with chelated complexes of Ag(III), nickel(IV) and copper(III). Reactions with excess Ti(II) yield Ti(III) and are strongly catalyzed by added Ti(IV), but stoichiometry is unaffected. Rapid reactions of Ti(II) with nonchelated oxidants, VO2+, and do not exhibit catalysis by Ti(IV). Reductions by Ti(III) are unaffected by Ti(IV). The Ag(III)-Ti(II) reaction, as catalyzed by Ti(IV), is subject to kinetic saturation with an association quotient 4 × 102 M−1 for the Ti(IV)-activated species. It is proposed that the catalyzed reductions of the Ag(III) and Ni(IV) oxidants are initiated by 1e− steps, but that the initially formed cation pairs undergo geminate follow-up reactions to give the observed stable products. 相似文献
6.
Mechanism of arsenic carcinogenesis: an integrated approach 总被引:33,自引:0,他引:33
Rossman TG 《Mutation research》2003,533(1-2):37-65
Epidemiological evidence shows an association between inorganic arsenic in drinking water and increased risk of skin, lung and bladder cancers. The lack of animal models has hindered mechanistic studies of arsenic carcinogenesis in the past, but some promising new models for these cancers are now available. The various forms of arsenic to which humans are exposed, either directly or via metabolism of inorganic arsenic to various methylated forms, further complicate the issue of mechanism, since these compounds can have different effects, both genotoxic and non-genotoxic. This review will try to integrate all of these issues, with a strong bias toward effects that are produced by environmentally relevant arsenic concentrations. 相似文献
7.
Joo-Yeon Han Astrid Gräslund Lars Thelander A. G. Sykes 《Journal of biological inorganic chemistry》1997,2(3):287-294
Four reductions of the R2 subunit of mouse ribonucleotide reductase have been studied and found to exhibit different behaviour
from that of Escherichia coli R2. An important difference is that there is no stable met-R2 (Fe2
II I) form of mouse R2. With hydroxyurea, hydrazine and hydroxylamine uniphasic kinetics are observed for the combined reduction
of radical Tyr ˙ and Fe2
II I components to tyrosine and Fe2
II respectively. The rate constants, determined at 370 nm (emphasising FeIII decay) and 417 nm (emphasising Tyr ˙ decay), differ by factors of 2–3, allowing some mechanistic features to be defined. The studies with hydrazine are particularly
important. In the case of E. coli R2, a first phase corresponding to two-equivalent reduction of the met-R2 component has been observed [18]. It is likely
that the four times slower second phase reaction of active E. coli R2 also corresponds to the Fe2
II I → Fe2
II change and is followed by fast intramolecular Fe2
II reduction of the higher potential Tyr ˙. The latter changes are believed to hold also for (active) mouse R2. The FeIIFeIII semi forms have been detected at low levels by EPR for mouse R2 (9%) and E. coli (∼5%) in previous studies. Further substrate reduction of FeIIFeIII occurs at a comparable rate to account for the transient behaviour of FeIIFeIII. For mouse R2 the combined FeIII decay processes (which we are unable to separate) give smaller uniphasic rate constants at 370 nm than at 417 nm. A fitted-base-line
(FBL) treatment of absorbance changes at 417 nm targets more closely the Tyr ˙ decay as a means of monitoring the rate-determining step. The FBL method gives rate constants k (M–1 s–1) at 25 °C and pH 7.5 for hydroxyurea (1.46), hydrazine (0.163) and hydroxylamine (4.4). Surprisingly, phenylhydrazine, with
a less strong reduction potential (0.25 V), gives a substantially faster reduction of the Tyr ˙ as the only redox step (rate constant 27 M–1 s–1). In this case a slower second phase at 370 nm is independent of reductant and corresponds to rate-controlling release of
FeIII. Overall the results indicate a more reactive redox centre for mouse R2 and help develop further an understanding of factors
affecting the reactivity of R2.
Received: 11 October 1996 / Accepted: 11 February 1997 相似文献
8.
9.
Johee Yoon Masayo Abe-Suzuki Pudjadi Eko Hiroshi Tamai Shigeichiro Hanamitsu Kaneyuki Nakane 《Ecological Research》2006,21(1):117-125
The hydroxyl (OH) radical, which is generated in polluted dew water on leaf surfaces of the Japanese apricot (Prunus mume), is known to be a potent oxidant. In order to investigate the effects of the OH radical formed in polluted dew water on the photosynthesis and growth of 3-year-old seedlings of P. mume, OH radical-generating solutions simulating polluted dew water were sprayed in the early morning as a mist throughout a growing season onto the leaf surfaces of seedlings growing in experimental greenhouses. Four OH radical-generating solutions (0, 6, 18 and 54 M H2O2 with Fe(III) and an oxalate ion) were used in the mist treatment. Five months after the beginning of treatment, the leaves exposed to the mist containing 54 M H2O2 showed a significantly smaller maximum CO2 assimilation rate (Amax) and stomatal conductance (gs) as compared to the leaves exposed to the mist containing 0 M H2O2. Exposure of P. mume seedlings to the OH radical-generating mist had caused a reduction in the dry weight and relative growth rate (RGR) of the above-ground parts (stem + branch) at the end of the growing season. A significant positive correlation was shown between RGR and Amax. Thus, the effects of oxidants generated in polluted dew water on leaf surfaces can be considered to be a cause of the decrease in leaf photosynthesis and growth of P. mume. 相似文献
10.
SIRT1 regulates oxidant- and cigarette smoke-induced eNOS acetylation in endothelial cells: Role of resveratrol 总被引:1,自引:0,他引:1
Endothelial nitric oxide synthase (eNOS) plays a crucial role in endothelial cell functions. SIRT1, a NAD+-dependent deacetylase, is shown to regulate endothelial function and hence any alteration in endothelial SIRT1 will affect normal vascular physiology. Cigarette smoke (CS)-mediated oxidative stress is implicated in endothelial dysfunction. However, the role of SIRT1 in regulation of eNOS by CS and oxidants are not known. We hypothesized that CS-mediated oxidative stress downregulates SIRT1 leading to acetylation of eNOS which results in reduced nitric oxide (NO)-mediated signaling and endothelial dysfunction. Human umbilical vein endothelial cells (HUVECs) exposed to cigarette smoke extract (CSE) and H2O2 showed decreased SIRT1 levels, activity, but increased phosphorylation concomitant with increased eNOS acetylation. Pre-treatment of endothelial cells with resveratrol significantly attenuated the CSE- and oxidant-mediated SIRT1 levels and eNOS acetylation. These findings suggest that CS- and oxidant-mediated reduction of SIRT1 is associated with acetylation of eNOS which have implications in endothelial dysfunction. 相似文献