摘要:

Dihydroplipoate and lipoate are physiological thiols which in addition to their coenzyme functions exhibit antioxidant activity. For NMR investigations of their protective mechanism in biological and model systems it is very important to know the full assignment of proton and carbon spectra of these molecules in water (D2O). An unambiguous assignment of proton and carbon NMR spectra has been made for dihydrolipoate and its short chain derivatives bisnor-and tetranor-lipoic acid in D2O and CDCl3solutions using 2D NMR methods.Oxidation of dihydrolipoic acid produces substantial electron density deshielding of the carbons nearest to the SH groups with the largest shift found at the inner SH group (17.79 ppm in D2O, 16.93 in CDCl3) and almost no changes in the tail portion of the molecule. However, bisnor-dihydrolipoic acid and especially tetranor-dihydrolipoic acid have more carbon deshielding near the outer SH group of the molecule which correlates with their known diminished ion chelating activity.Moreover, the proton triplet at position 2 of lipoic acid has strong pH dependence (pK = 4.58) due to the close proximity to the carboxylic group and this feature may be used for monitoring pH.

ISSN:1071-5762    

DOI:10.3109/10715769609149045

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

A recently developed method has been utilized to demonstrate the generation of hydroxyl radicals (HObullet) in the immediate proximity of DNA by cop-per(II)/iron(HI)–adriamycin in the presence of ascorbate and hydrogen peroxide. SECCA, a succinylated derivative of coumarin, generates the fluorescent 7-hydroxy-SECCA following reaction with HObullet. SECCA was coupled to polylysine or to histone HI and then complexed to DNA. When HO' was generated in the proximity of DNA by polylysine-coupled iodine-125, which emits short range Auger electrons, 7-hydroxy-SECCA was produced. DMSO was only moderately efficient in reducing the fluorescence induction, demonstrating the“local”generation of HObulletin this system. Copper(II)/iron(III)–adriamycin in the presence of ascorbate and hydrogen peroxide generated the fluorescent 7-hydroxy-SECCA both when SECCA was free in solution and when SECCA was DNA-conjugated. With SECCA free in solution, the fluorescence induction was almost eliminated in the presence of HObulletscavengers (ethanol, tertbutanol or DMSO) and the relative efficiency of the scavengers in reducing the fluorescence followed their rate constant with HObullet. Furthermore, SECCA incubated with a singlet oxygen-generating compound demonstrated no fluorescence induction. When SECCA was positioned in close proximity to DNA as a SECCA-histone-H1–DNA complex, the relative efficiency of the scavengers in reducing the fluorescence still followed their rate constant with HO'; overall however the scavengers were much less effective in reducing the fluorescence, due presumably to the formation of HObulletradical in the immediate vicinity of DNA. These data suggest that copper(II)/iron(III)–adriamycin produces HO' in the presence of ascorbate and hydrogen peroxide whether unbound or bound to DNA and suggest that in the latter case scavengers would not prevent HObulletfrom attacking chromatin. In addition, the ability of DMSO to trap HObulletwas shown to decrease as the conformation of the HI–DNA complex becomes more compact indicating the strong dependence of the trapping ability on chromatin conformation.

ISSN:1071-5762    

DOI:10.3109/10715769609149046

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

A study conducted on Fe2+autoxidation showed that its rate was extremely slow at acidic pH values and increased by increasing the pH; it was stimulated by Fe3+addition but the stimulation did not present a maximum at a Fe2+/Fe3+ratio approaching 1:1. The species generated during Fe3+-catalyzed Fe2+autoxidation was able to oxidize deoxyribose; the increased Fe2+oxidation observed at higher pHs was paralleled by increased deoxyribose degradation. The species generated during Fe3+-catalyzed Fe2+autoxidation could not initiate lipid peroxidation in phosphatidylcholine liposomes from which lipid hydroperoxides (LOOH) had been removed by treatment with triph-enylphosphine. Neither Fe2+oxidation nor changes in the oxidation index of the liposomes due to lipid peroxidation were observed at pHs where the Fe3+effect on Fe2+autoxidation and on deoxyribose degradation was evident. In our experimental system, a Fe2+/Fe3+ratio ranging from 1:3 to 2:1 was unable to initiate lipid peroxidation in LOOH-free phosphatidylcholine liposomes. By contrast Fe3+stimulated the peroxidation of liposomes where increasing amounts of cumene hydroperoxide were incorporated. These results argue against the participation of Fe3+in the initiation of LOOH-independent lipid peroxidation and suggest its possible involvement in LOOH-dependent lipid peroxidation.

ISSN:1071-5762    

DOI:10.3109/10715769609149047

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

We assessed the effect of varying levels of hyperoxia on14C-albumin flux across bovine pulmonary artery endothelial cell (BPAEC) monolayers. Endothelialized nitrocellulose filters were mounted in Ussing-type chambers which were filled with cell culture medium (M 199). Equimolar amounts of14C-labeled and unlabeled albumin were added to the“hot”and“cold”chambers, respectively, and the monolayers were exposed to 3 hours of varying levels of oxygen (16%, 30%, 40%, 60%, and 95%). When compared to 16% O2, exposure to hyperoxic gas mixtures of 40% or greater progressively increased albumin permeability across endothelial monolayers within 3 hours to a value 2.5 times higher at 95% O2compared to 16% O2(p<0.001). Hyperoxia-induced permeability increases were prevented by catalase, superoxide dismutase, desferriox-amine, and allopurinol. Our data indicate that hyperoxia induces endothelial permeability changes more rapidly than previously reported even at O2concentrations as low as 40%.

ISSN:1071-5762    

DOI:10.3109/10715769609149048

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Individuals with low serum cholesterol experience greater than expected age-adjusted mortality from non-atherosclerotic diseases, including cancer, respiratory and digestive illnesses, but the basis for these associations remains unclear. The current investigation considered the hypothesis that hypocholesterolemia is associated with reduced antioxidant reserve. Serum total antioxidant activity as well as concentrations of vitamin E, vitamin C, and thiols were compared in two groups of 24 subjects distinct in both mean low density lipoprotein (LDL) cholesterol (2.3 v. 4.9 mM) and mean total cholesterol (4.3 v. 7.0 mM). The low and high cholesterol groups were equivalent in gender mix, age, weight, and serum total protein. Results reveal that compared with the high group, the low cholesterol group had decreased total serum antioxidant activity (p<.05). Thiol concentrations were also lower in the low cholesterol group (p<.05). Group differences in serum total antioxidant activity and thiol concentration were larger among men than women. The two groups did not differ in vitamin C. Low cholesterol was associated with reduced absolute vitamin E levels, although the tocopherol: cholesterol ratio was the same in low and high cholesterol individuals. These data indicate that hypocholesterolemia may be associated with low serum antioxidant reserve, possibly increasing susceptibility to oxidative stress.

ISSN:1071-5762    

DOI:10.3109/10715769609149049

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

The relationship between O2and an active oxygen scavenging system inChlorella vulgarisvar.vulgaris(IAM C-534) was investigated. WhenChlorella vulgariswas exposed to 2% O2, only traces of active oxygen scavenging enzymes were found. When theChlorella vulgariswas treated with 20% or 50% O2, it was shown that the level of enzyme activity increased as the O2concentration increased. An increase in enzyme activity was not found in any specific enzyme but in all of the enzymes, but the level of glutathione and ascorbate remained the same in all the cases. In addition, the photosynthetic efficiency also decreased as the concentration of O2was increased. These results suggest that an O2enriched environment can lead to an increase in the production of active oxygen species such as Obullet2and H2O2and to a decrease in the photosynthetic efficiency inChlorella vulgaris. The hydroxyl radical (bulletOH) was detected directly in theChlorella vulgarissuspension with a spin trapping reagent. It was also clear that the increase in thebulletOH intensity as the visible light intensity increased was unrelated to the O2concentration. It was suggested that the conditions for producingbulletOH and the other active oxygen species were different, and that two types of oxygen stress should exist in theChlorella vulgaris.

ISSN:1071-5762    

DOI:10.3109/10715769609149050

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Structures ofα-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) radical adducts formed in the reactions of soybean lipoxygenase with linoleic acid, linolenic acid, and arachidonic acid were determined using continuous flow fast atom bombardment (CF-FAB) combined with tandem mass spectrometry. The radical adducts of these lipoxygenase-dependent reactions were: n-octanoic acid radical, 12,13-dihydroxylinoleic acid radical, 12,13-epoxylinoleic acid radical, and n-pentyl radical from linoleic acid; n-octanoic acid radical, ethyl radical, andcis/transand/or positional isomers (1- and 3-pentenyl) of pentenyl radical from linolenic acid; and 14,15-epoxyarachidonic acid radical and n-pentyl radical from arachidonic acid. Of these radical adducts, the n-octanoic acid radical from linoleic and linolenic acid, the ethyl radical from linolenic acid, and the 12,13-dihydroxylinoleic acid radical are identified for the first time in the reactions of soybean lipoxygenase. Thus the CF-FAB combined with tandem mass spectrometry employed here, by which both radical adducts and their fragment ions can be detected, is shown to be a powerful tool in the structural identification of free radicals.

ISSN:1071-5762    

DOI:10.3109/10715769609149051

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Peroxynitrite, formed by reaction of superoxide and nitric oxide, appears to be an important tissue-damaging species generated at sites of inflammation. In this paper, we compare the abilities of several biological antioxidants to protect against peroxynitrite-dependent inactivation ofα1-antiproteinase, and to inhibit tyrosine nitration upon addition of peroxynitrite. GSH and ascorbate protected efficiently in both systems. Uric acid inhibited tyrosine nitration but notα1-antiproteinase inactivation. The possibility that ascorbic acid is an important scavenger of reactive nitrogen speciesin vivois discussed.

ISSN:1071-5762    

DOI:10.3109/10715769609149052

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor