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1.
The effect of commonly used food antioxidants on recombinant tumor necrosis factor alpha (rTNF-alpha)-induced cytotoxicity, growth enhancement and adhesion has been evaluated. Butylated hydroxyanisole (BHA) and 4-hydroxymethyl-2,6-di-t-butylphenol (HBP) were the only two of nine antioxidants that completely inhibited rTNF-alpha-induced cytotoxicity in L929 and WEHI 164 fibrosarcoma cells. Ethoxyquin, propyl gallate and butylated hydroquinone only partially inhibited rTNF-alpha-induced cytotoxicity, while the antioxidants butylated hydroxytoluene (BHT), alpha-tocopherol, ascorbic acid and thiodipropionic acid had minimal effects. The only difference between the molecular structure of the efficient HBP and the non-efficient BHT, is a hydroxymethyl group instead of a hydroxyl group on the phenolic ring. Neither BHA nor BHT inhibited the activation of NF kappa B after 10 or 60 min challenge with rTNF-alpha in L929 cells. BHA also inhibited rTNF-alpha-induced, but not rIL-1 beta-induced growth enhancement in FS-4 fibroblasts. Further, BHA blocked both rTNF-alpha-induced and rIL-1 beta-induced prostaglandin E2 synthesis in FS-4 fibroblasts. BHA inhibited the rTNF-alpha-induced release of arachidonic acid in both FS-4 and L929 cells, suggesting that BHA inhibits cellular phospholipase(s). Neither alpha-tocopherol nor BHA inhibited rTNF-alpha-induced adhesiveness of human endothelial cells. The results indicate that BHA is a specific and potent inhibitor of rTNF-alpha- and rTNF-beta-induced cytotoxicity, as well as of rTNF-alpha-induced growth enhancement. 相似文献
2.
Criado S Allevi C Ceballos C García NA 《Redox report : communications in free radical research》2007,12(6):282-288
Visible-light photo-irradiation of the commercial phenolic antioxidants (PhAs) butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), in the presence of vitamin B2 (riboflavin, Rf), in methanolic solutions and under aerobic conditions, results in the photo-oxidation of the PhAs. The synthetic dye photosensitiser Rose Bengal was also employed for auxiliary experiments. With concentrations of riboflavin and PhAs of ca. 0.02 mM and < 1 mM, respectively, the excited triplet state of the vitamin (3Rf*) is quenched by BHT in a competitive fashion with dissolved ground state triplet oxygen. From the quenching of 3Rf*, the semireduced form of the pigment is generated through an electron transfer process from BHT, with the subsequent production of superoxide anion radical (O2*-) by reaction with dissolved molecular oxygen. In parallel, the species singlet molecular oxygen, O2(1delta(g)), is also generated. Both reactive oxygen species produce the photodegradation of BHT. In the case of BHA, the lack of any effect exerted by superoxide dismutase drives out a significant participation of a O2(*-)-mediated mechanism. BHA mainly interacts with O2(1delta(g)) and exhibits a desirable property as an antioxidant--a relatively high capacity for O2(1delta(g)) de-activation and a low photodegradation efficiency by the oxidative species. Electrochemical determinations support the proposed photodegradative mechanism. 相似文献
3.
Phenolic antioxidants butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) at concentration 0.55 mM and 2.25 mM, respectively, added to cultures of Streptomyces cinnamonensis C-100-5 caused up to 380% higher production of polyether antibiotic monensin. S. cinnamonensis exhibits high tolerance to BHT, but it is more sensitive towards BHA. 5.5 mM BHA practically stopped growth, while 45 mM BHT still stimulated antibiotic production. Another antioxidants probucol and tocoferol acetate did not exert such positive effects. BHA was predominantly metabolised to 5-hydroxy-BHA. When BHA and BHT were applied simultaneously, the main transformation metabolite was 3,3,5,5-tetra-tert-butyl-stilbene-4,4-quinone accompanied by 1,2-bis(3,5-di-tert-butyl-4-hydroxyphenyl)ethane. 相似文献
4.
Butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) were used to determine any effects on the N-acetyltransferase (NAT) activity in rat whole blood and white blood cells as measured by high performance liquid chromatography assay for the amounts of N-acetyl-2-aminofluorene (AAF) and 2-aminofluorene (AF). Two assay systems were performed, one with cellular cytosols, the other with intact white blood cells. The NAT activity in the whole blood and white blood cell cytosols was suppressed by BHA and BHT in a dose-dependent manner, i.e. the higher the concentrations of BHA and BHT, the higher the inhibition of NAT activity. Time-course experiments showed that NAT activity measured from the intact white blood cells was inhibited by BHA and BHT up to 24 h. The results suggest that BHA and BHT suppressed AF acetylation in rat blood with intact white blood cells. 相似文献
5.
The food antioxidants butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are shown to be metabolized to covalent binding intermediates and various other metabolites by prostaglandin H synthase and horseradish peroxidase. BHA was extensively metabolized by horseradish peroxidase (80% conversion of parent BHA into metabolites) resulting in the formation of three dimeric products. Only two of these dimers were observed in prostaglandin H synthase-catalyzed reactions. In contrast to BHA, BHT proved to be a relatively poor substrate for prostaglandin synthase and horseradish peroxidase, resulting in the formation of a small amount of polar and aqueous metabolites (23% conversion of parent BHT into metabolites). With arachidonic acid as the substrate, prostaglandin H synthase catalyzed the covalent binding of [14C]BHA and [14C]BHT to microsomal protein which was significantly inhibited by indomethacin and glutathione. The covalent binding of BHA and its metabolism to dimeric products were also inhibited by BHT. In contrast, the addition of BHA enhanced the covalent binding of BHT by 400%. Moreover, in the presence of BHA, the formation of the polar and aqueous metabolites of BHT was increased and two additional metabolites, BHT-quinone methide and stilbenequinone, were detected. The increased peroxidase-dependent oxidation of BHT in the presence of BHA is proposed to occur via the direct chemical interaction of BHA phenoxyl radical with BHT or BHT phenoxyl radical. These results suggest a potential role for phenoxyl radicals in the activation of xenobiotic chemicals to toxic metabolites. 相似文献
6.
Butylated hydroxyanisole (BHA), Butylated hydroxytoluene (BHT) and tertiary butylhydroquinone (TBHQ) alone in cultural media were tested for the inhibition of growth and luteoskyrin production by two toxigenic strains ofPenicillium islandicum UST-11 andP. islandicum HLT-6. In potato dextrose agar, the concentrations of BHA and TBHQ from 0.2 mg/disc, BHT from 5.0 mg/disc did affect the growth of both tested strains, but the initial concentrations of these antioxidants to reduced luteoskyrin production by UST-11 strain were BHA 0.5 mg/disc, BHT 1.0 mg/disc and TBHQ 0.4 mg/disc, while for HLT-6, BHA 0.4 mg/disc, BHT and TBHQ were 0.2 mg/disc, respectively. In grainy and powdery rice media, the effects of BHA, BHT and TBHQ on luteoskyrin production byP. islandicum UST-11 and HLT-6 were clearly demonstrated. The efficiency of the inhibitory effect was not only closely related to the concentration of antioxidants, but also completely inhibited the luteoskyrin production at a concentration of 200 mg/kg or higher. Also, the antioxidants at a concentration higher than 20 mg/kg reduced significantly the growth and luteoskyrin production by both strains ofP. islandicum. 相似文献
7.
Control of Aspergillus growth and aflatoxin production using antioxidants at different conditions of water activity and pH 总被引:5,自引:0,他引:5
AIMS: The effect of butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), trihydroxybutyrophenone (THB) and propyl paraben (PP) (at concentrations of 1, 10 and 20 mmol l(-1)) on germination, growth and aflatoxin B1 production by Aspergillus section Flavi was evaluated. METHODS AND RESULTS: Studies on the percentage of spore germination, elongation rate, growth rate and aflatoxin B1 production were carried out in vitro in relation to water activity (aw) at 0.982, 0.937, 0.809 and 0.747 values. At 0.809 and 0.747aw values none of the isolates was able to germinate. Overall, PP and BHA were the antioxidants most effective at inhibiting germination of both species. In the presence of the lowest concentration of BHA and PP (1 mmol l(-1)) the conidial germination percentage ranged from 2 to 19% after 15 h of incubation at the highest water activity tested. BHA and PP at 10-20 mmol l(-1) completely inhibited conidial germination. The antioxidants more efficient in controlling Aspergillus elongation rate were PP, BHT and BHA. All strains were much more sensitive to all antioxidants tested on the percentage of spore germination and growth rate at 0.937aw. The antioxidants PP and BHA completely inhibited aflatoxin B1 production by all strains when added at 1 mmol l(-1). Decreased aflatoxin B1 levels in comparison with the control, were observed with BHT at 1, 10 and 20 mmol(-1) with the strain T20 at 0.982aw. In contrast, stimulation was observed with the antioxidant THB at 10 and 20 mmol l(-1) at 0.937aw with the strains T20 and T23. The effect of BHA and PP at 1 mmol l(-1) on lag phase and growth rate was maintained in the pH range between 6 and 8. At all pH values the inhibitory effect of BHA was higher than PP. No aflatoxin B1 was detected at all pH values. CONCLUSIONS: The data show that BHA and PP could be considered as effective fungitoxicants for A. flavus and A. parasiticus. SIGNIFICANCE AND IMPACT OF THE STUDY: The information obtained show promise for controlling growth and aflatoxin B1 in stored maize. Futher studies should be carried out to examine the potential for antioxidants, such as BHA and PP to effectively control both growth and aflatoxin production. 相似文献
8.
《Redox report : communications in free radical research》2013,18(6):282-288
AbstractVisible-light photo-irradiation of the commercial phenolic antioxidants (PhAs) butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), in the presence of vitamin B2 (riboflavin, Rf), in methanolic solutions and under aerobic conditions, results in the photo-oxidation of the PhAs. The synthetic dye photosensitiser Rose Bengal was also employed for auxiliary experiments. With concentrations of riboflavin and PhAs of ca. 0.02 mM and < 1 mM, respectively, the excited triplet state of the vitamin (3Rf*) is quenched by BHT in a competitive fashion with dissolved ground state triplet oxygen. From the quenching of 3Rf*, the semireduced form of the pigment is generated through an electron transfer process from BHT, with the subsequent production of superoxide anion radical (O2??) by reaction with dissolved molecular oxygen. In parallel, the species singlet molecular oxygen, O2(1Δg), is also generated. Both reactive oxygen species produce the photodegradation of BHT. In the case of BHA, the lack of any effect exerted by superoxide dismutase drives out a significant participation of a O2??-mediated mechanism. BHA mainly interacts with O2(1Δg) and exhibits a desirable property as an antioxidant – a relatively high capacity for O2(1Δg) de-activation and a low photodegradation efficiency by the oxidative species. Electrochemical determinations support the proposed photodegradative mechanism. 相似文献
9.
Etcheverry M Torres A Ramirez ML Chulze S Magan N 《Journal of applied microbiology》2002,92(4):624-632
AIMS: To examine the effect of butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), trihydroxybutyrophenone and propylparaben (PP) (at concentrations of 1-20 mmol l(-1)) on growth of and fumonisin production by Argentinian strains of Fusarium verticillioides and F. proliferatum. METHODS AND RESULTS: Studies on lag phases prior to growth, relative growth rates and fumonisin concentrations were carried out in vitro in relation to water activity (0.995-0.93 a(w)) and temperature (18 and 25 degrees C) on a maize meal agar. Overall, PP was the antioxidant which was most effective at inhibiting strains of both species. The lag phase prior to growth and growth rates were significantly decreased by PP and BHA at 10 and 20 mmol l(-1), regardless of the temperature or aw level tested. Total fumonisin production was higher at 0.98 a(w) and decreased by about 45-50% at 0.995 and 0.95 a(w). Overall, BHT only inhibited fumonisin production at 0.95 aw at 10 and 20 mmol l(-1), while BHA was effective at most a(w) levels tested at 10 and 20 mmol l(-1). Propylparaben completely inhibited fumonisin production by both F. verticillioides and F. proliferatum at > 1 mmol l(-1), regardless of the temperature or a(w) level. Small interstrain differences in the levels of inhibition by the antioxidants were observed for three F. verticillioides and four F. proliferatum strains at 0.995, 0.98 and 0.95 a(w). Propylparaben and BHA completely inhibited the growth of both species at the concentrations evaluated, regardless of the a(w) level. CONCLUSIONS: Two antioxidants show promise for the control of growth of and fumonisin production by these species over a wide range of environmental conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: Potential exists for using such food-grade preservatives for prevention of mycotoxigenic fungi and their toxins entering the food chain. 相似文献
10.
The “in vitro” effects of α-tocopherol, butylhydroxytoluene (BHT) and butylhydroxyanisole (BHA) were studied on aggregation of human platelets induced by collagen and arachidonic acid (AA), on the metabolic conversion of 14C AA through the cyclooxygenase and lipoxygenase pathways and on the formation of thromboxane B2 (TXB2) in washed platelets after stimulation with collagen.Vitamin E completely inhibited AA induced platelet aggregation only at high concentration (mM) and after 10 minutes of preincubation, with limited effects on AA metabolism in platelets and no effect on TXB2 formation from endogenous substrate. BHA completely inhibited platelet aggregation in the 10−6M range, gave 50% inhibition of AA metabolism in the 10−5M range and almost complete inhibition of thromboxane formation in the 10−4M range. BHT was about 100 times less active on platelet aggregation and AA metabolism. The lipoxygenase and cyclooxygenase pathways were differentially affected at low concentrations of BHA and only at concentrations greater than 5×10−5M were both pathways depressed. 相似文献
11.
Chung S. Yang Wasyl Sydor Mary B. Martin Katherine F. Lewis 《Chemico-biological interactions》1981,37(3):337-350
The effects of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) on the aryl hydrocarbon hydroxylase (AHH) activities in the liver, lung and skin of rats and mice have been studied to examine the possible mechanisms of the anticarcinogenic actions of these compounds. Both compounds inhibit the hydroxylase activities of hepatic microsomes and nuclei, with BHA a more potent inhibitor than BHT. The AHH of lung microsomes is inhibited to a lesser extent by BHA and BHT than that of the liver. The AHH activities of both liver and lung microsomes become less susceptible to the inhibition after pretreatment of the animals with 3-methylcholanthrene (MC) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) but phenobarbital (PB) pretreatment does not produce such an effect. In skin homogenates, however, the AHH activities of control rats and mice are not inhibited by BHA and BHT. The only skin sample which is inhibited by BHA and BHT is that from TCDD-pretreated mice. It has been established that the extent of inhibition with different samples is related to the concentration of BHA in the incubation but not to the amounts or specific activities of microsomes used. Double reciprocal plots suggest that BHA exerts a mixed inhibition on the hydroxylase of liver microsomes with a Ki of 7.7 μM. Analysis of the metabolites of benzo[a]pyrene (BP) shows that BHA inhibits the formation of various metabolites uniformly without changing the regio-selectivity of the enzyme system. The mechanism of inhibition has also been studied with a reconstituted AHH system consisting of cytochrome P-450 (P-450), reductase and phospholipid. The system with P-450 isolated from PB-induced microsomes is inhibited to a much greater extent than that with MC-induced P-450. The results indicate that the inhibitory action of BHA is dependent on the species of the animal, tissue types and treatment with inducers. 相似文献
12.
Antioxidant and radical scavenging properties of curcumin 总被引:3,自引:0,他引:3
Curcumin (diferuoyl methane) is a phenolic compound and a major component of Curcuma longa L. In the present paper, we determined the antioxidant activity of curcumin by employing various in vitro antioxidant assays such as 1,1-diphenyl-2-picryl-hydrazyl free radical (DPPH*) scavenging, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging activity, N,N-dimethyl-p-phenylenediamine dihydrochloride (DMPD) radical scavenging activity, total antioxidant activity determination by ferric thiocyanate, total reducing ability determination by the Fe(3+)-Fe(2+) transformation method, superoxide anion radical scavenging by the riboflavin/methionine/illuminate system, hydrogen peroxide scavenging and ferrous ions (Fe(2+)) chelating activities. Curcumin inhibited 97.3% lipid peroxidation of linoleic acid emulsion at 15 microg/mL concentration (20 mM). On the other hand, butylated hydroxyanisole (BHA, 123 mM), butylated hydroxytoluene (BHT, 102 mM), alpha-tocopherol (51 mM) and trolox (90 mM) as standard antioxidants indicated inhibition of 95.4, 99.7, 84.6 and 95.6% on peroxidation of linoleic acid emulsion at 45 microg/mL concentration, respectively. In addition, curcumin had an effective DPPH* scavenging, ABTS*(+) scavenging, DMPD*(+) scavenging, superoxide anion radical scavenging, hydrogen peroxide scavenging, ferric ions (Fe(3+)) reducing power and ferrous ions (Fe(2+)) chelating activities. Also, BHA, BHT, alpha-tocopherol and trolox, were used as the reference antioxidant and radical scavenger compounds. According to the present study, curcumin can be used in the pharmacological and food industry because of these properties. 相似文献
13.
Enhancement of the peroxidase-mediated oxidation of butylated hydroxytoluene to a quinone methide by phenolic and amine compounds 总被引:1,自引:0,他引:1
We have recently demonstrated that butylated hydroxyanisole (BHA) markedly stimulates the peroxidase-dependent oxidation of butylated hydroxytoluene (BHT) to the potentially toxic BHT-quinone methide. Using both horseradish peroxidase and prostaglandin H synthase we now report the ability of a wide variety of compounds to stimulate peroxidase-dependent activation of BHT. These compounds include several phenolic compounds commonly present in pharmacologic preparations or occurring naturally in foods. The ability of a given compound to stimulate BHT oxidation was found to depend on the type of radical it forms upon peroxidase oxidation. Compounds which have been shown to form phenoxy radicals or nitrogen-centered cation radicals were observed to enhance BHT oxidation. Conversely, compounds which are known to form peroxy radicals or semiquinone radicals either inhibited or had no effect on BHT oxidation. Compounds which enhanced BHT oxidation (monitored by covalent binding of [14C]BHT to protein) were also observed to stimulate the formation of BHT-quinone methide and stilbenequinone. This suggested a common mechanism of interaction of these compounds with BHT. The stimulation of BHT covalent binding by BHA was also seen in various human and animal tissues using either arachidonic acid or hydrogen peroxide as substrate. The possible toxicologic implications of the enhancement of peroxidase-catalyzed BHT oxidation to BHT-quinone methide are discussed. 相似文献
14.
AIMS: The effectiveness of the food-grade antioxidants butylated hydroxytoluene (BHT), trihydroxybutyrophenone (THB), propyl paraben (PP) and butylated hydroxyanisole (BHA) at 1, 10 and 20 mmol l(-1) concentrations on germination, growth, and aflatoxin B(1) (AFB(1)) production by Aspergillus section Flavi strains was determined. METHODS AND RESULTS: Assays on the lag phase of germination, germination percentage, germ tube elongation rate, lag phase, growth rate and AFB(1) production by three strains of Aspergillus flavus and three of Aspergillus parasiticus were carried out in vitro on peanut extract meal agar conditioned at different water activities (a(w): 0.982, 0.971, 0.955, 0.937). The antioxidants PP and BHA efficiently inhibited the germination of the two species tested at the doses 10 and 20 mmol(-1). The antioxidants PP and BHA at 1 mmol l(-1) and THB at 20 mmol l(-1) reduced the germ tube elongation rate most effectively, regardless of a(w) levels. An increase in the lag time and a reduction in the growth rate of 100% of the strains was observed, this was due to the action of BHT at the doses 10 and 20 mmol(-1) at 0.982, 0.971 and 0.955 a(w), although these treatments stimulated the AFB(1) accumulation in most of the fungi tested. The more effective antioxidants were PP and BHA, which increased the lag phase, reduced the growth rate and AFB(1) production in all of the strains at the four a(w) assayed. At concentrations 10 and 20 mmol l(-1), these antioxidants totally inhibited fungal development. CONCLUSIONS: The study shows that the antioxidants BHA and PP are effective fungal inhibitors to peanut Aspergillus section Flavi in wide range of water activity. SIGNIFICANCE AND IMPACT OF THE STUDY: The results suggest that phenolic antioxidants, BHA and PP, can be effective fungitoxicants on aflatoxigenic strains in peanut at industrial level. 相似文献
15.
Clerici F Gelmi ML Yokoyama K Pocar D Van Voorhis WC Buckner FS Gelb MH 《Bioorganic & medicinal chemistry letters》2002,12(16):2217-2220
A series of isothiazole dioxides was synthesized and evaluated as inhibitors of protein farnesyltransferase from the parasite that causes African sleeping sickness (Trypanosoma brucei). The most potent compound in the series inhibited the parasite enzyme with an IC(50) of 2 microM and blocked the growth of the bloodstream parasite in vitro with an ED(50) of 10 microM. The same compound inhibited rat protein farnesyltransferase and protein geranylgeranyltransferase type I only at much higher concentration. 相似文献
16.
Trypanosoma brucei, a eukaryotic pathogen that causes African sleeping sickness in humans and nagana in cattle, depends on the enzyme acetyl-CoA carboxylase (ACC) for full virulence in mice. ACC produces malonyl-CoA, the two carbon donor for fatty acid synthesis. We assessed the effect of haloxyfop, an aryloxyphenoxypropionate herbicide inhibitor of plastid ACCs in many plants as well as Toxoplasma gondii, on T. brucei ACC activity and growth in culture. Haloxyfop inhibited TbACC in cell lysate (EC(50) 67 μM), despite the presence of an amino acid motif typically associated with resistance. Haloxyfop also reduced growth of bloodstream and procyclic form parasites (EC(50) of 0.8 and 1.2 mM). However, the effect on growth was likely due to off-target effects because haloxyfop treatment had no effect on fatty acid elongation or incorporation into complex lipids in vivo. 相似文献
17.
儿茶素分光光度法与微量法抗氧化活性研究 总被引:1,自引:0,他引:1
为比较微量法和分光光度法的差异,以Trolox为参比物,PG、BHA和BHT为阳性对照品,比较其IC50和TEAC;以儿茶素的抗氧化活性为研究对象,对2种方法的相关性做Paired—samplet t est。发现2种方法所得到的TEAC基本一致,4个标准品和儿茶素的抗氧化活性顺序一致,即:PG〉儿茶素〉BHA〉Trolox〉BHT;2种方法的相关系数r=0.998,显著性P=0.501。研究结果表明,分光光度法操作繁琐费时,用样量大;微量法操作简单快速,用样量小,准确性好,适合对微量天然产物抗氧化活性的评价。 相似文献
18.
《Journal of Fermentation Technology》1986,64(2):119-127
An excess of copper incorporated into Tetrahymena cells was mainly distributed in mitochondria, and inhibited oxygen uptake of Tetrahymena cells. The inhibition of oxygen uptake was clearly to copper uptake in mitochondria. Succinate was most favorable as a substrate stimulating oxygen uptake in mitochondria, and oxygen uptake was most strongly inhibited by copper (0.1 mM) in the presence of succinate among various substrates. The copper incorporated into mitochondria was in the fraction with the inner membranes. Succinate dehydrogenase (SDH) was inhibited at the lowest copper concentration (0.1 mM) among respiratory related enzymes. The redox potential of respiratory components was raised by copper. These results suggest that respiratory inhibition of Tetrahymena cells by copper may be mainly cause by inhibition of SDH as a FAD-protein and oxidation of electron carriers. At higher copper concentrations, MDH, cytochrome c reductase, and ATP synthesis were also inhibited. Growth inhibition may be due to these effects of copper in mitochondria. Mercury affected both oxygen uptake and SDH more strongly than copper. Zinc (0.1 mM) also affected oxygen uptake in mitochondria and a little in whole cells, however, it did not inhibit SDH. Cobalt, manganese, and nickel affected both oxygen uptake and SDH only a little at the same concentration (0.1 mM) as copper. 相似文献
19.
A sensitive method for the detection of small quantities of hydrophobic antioxidant free radical scavengers such as butylatedhydroxytoluene (BHT) and butylatedhydroxyanisole (BHA) in aqueous samples is described. The procedure involves extraction of the hydrophobic free radical scavenger into an organic solvent phase, followed by the subsequent reaction of an aliquot of this extract with the stable cation radical tris(p-bromophenyl)amminium hexachloroantimonate (TBACA). In experiments with BHT and BHA, the loss of TBACA absorbance at 730 nm was found to be linearly proportional to the amount of antioxidant added, with quantities of BHT as small as 200 pmol being easily detectable. In aqueous suspensions of dimyristoylphosphatidylcholine vesicles, assays of the aqueous BHT concentration showed that BHT partitioned strongly into the membrane phase, achieving very high BHT/phospholipid ratios. For a given concentration of BHT, partitioning into the membrane phase was greater in large, multilamellar liposomes than in either small, single-walled vesicles or in purified rat brain synaptic vesicle membranes. Direct assay of BHT and BHA in phospholipid membranes, however, was complicated by a nonspecific interaction between TBACA and the phospholipid. 相似文献
20.
The inhibitory effects of 2-hydroxybiphenyl on various electron transport reactions of isolated membranes and growth in the presence of malate of either phototrophic or chemotrophic cells of Rhodospirillum rubrum were studied. 50% inhibition of both oxygen uptake of whole cells and growth under chemotrophic conditions (i.e. aerobiosis in the dark) was achieved in the presence of 0.09 mM 2-hydroxybiphenyl. With isolated membranes the same effect on NADH oxidase was obtained with 0.08 mM of inhibitor. Succinate dependent respiratory reactions were inhibited by 50% at a concentration of 0.36 mM. Growth under phototrophic conditions (i.e. anaerobiosis in the light) was inhibited by 50% in the presence of 0.17 mM (wild type strain) or 0.21 mM (blue-green mutant, strain VI) of 2-hydroxybiphenyl. Photophosphorylation and light dependent NAD+ reduction by succinate were inhibited by 50% at concentrations of 0.21 mM and 0.03 mM of inhibitor, respectively. After phototrophic growth of the organisms for about five doublings of cell mass in the presence of 0.18 mM of 2-hydroxybiphenyl coloured carotenoids could no longer be detected. Membrane fractions of such cultures exhibited normal activities of succinate cytochrome c reductase but activities of NADH cytochrome c reductase were decreased by 80%. In comparison with a blue green mutant, strain VI, of R. rubrum light induced absorbance changes at 865 nm as well as activities of photophosphorylation were unaffected. However, no activity of light dependent NAD+ reduction with succinate could be detected. The data indicate that cellular respiration as well as chemotrophic growth depend largely on NADH dependent respiration. Phototrophic growth, on the other hand, is limited by photophosphorylation while energy dependent reversed electron flow to NAD+, if at all, is of rathe minor importance.Abbreviation BChl
bacteriochlorophyll 相似文献