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51.
Take-all is a world-wide root-rotting disease of cereals. The causal organism of take-all of wheat is the soil-borne fungus Gaeumannomyces graminis var tritici (Ggt). No resistance to take-all, worthy of inclusion in a plant breeding programme, has been discovered in wheat but the severity of take-all is increased in host plants whose tissues are deficient for manganese (Mn). Take-all of wheat will be decreased by all techniques which lift Mn concentrations in shoots and roots of Mn-deficient hosts to adequate levels. Wheat seedlings were grown in a Mn-deficient calcareous sand in small pots and inoculated with four field isolates of Ggt. Infection by three virulent isolates was increased under conditions which were Mn deficient for the wheat host but infection by a weakly virulent isolate, already low, was further decreased. Only the three virulent isolates caused visible oxidation of Mn in vitro. The sensitivity of Ggt isolates to manganous ions in vitro did not explain the extent of infection they caused on wheat hosts. In a similar experiment four Australian wheat genotypes were grown in the same Mn-deficient calcareous sand and inoculated with one virulent isolate of Ggt. Two genotypes were inefficient at taking up manganese and were very susceptible to take-all, one was very efficient at taking up manganese and was resistant to take-all, and the fourth genotype was intermediate for both characters. All genotypes were equally resistant under Mn-adequate conditions. 相似文献
52.
Most carcinogens, including polycyclic aromatic hydrocarbons (PAH), require metabolic activation to produce the ultimate electrophilic species that bind covalently with cellular macromolecules to trigger the cancer process. Metabolic activation of PAH can be understood in terms of two main pathways: one-electron oxidation to yield reactive intermediate radical cations and monooxygenation to produce bay-region diol epoxides. The reason we have postulated that one-electron oxidation plays an important role in the activation of PAH derives from certain common characteristics of the radical cation chemistry of the most potent carcinogenic PAH. Two main features common to these PAH are: 1) a relatively low ionization potential, which allows easy metabolic removal of one electron, and 2) charge localization in the PAH radical cation that renders this intermediate specifically and efficiently reactive toward nucleophiles. Equally important, cytochrome P-450 and mammalian peroxidases catalyze one-electron oxidation. This mechanism plays a role in the binding of PAH to DNA. Chemical, biochemical and biological evidence will be presented supporting the important role of one-electron oxidation in the activation of PAH leading to initiation of cancer. 相似文献
53.
H. N. Ravishankar Aparna V. S. Rao T. Ramasarma 《Molecular and cellular biochemistry》1996,154(2):101-106
Sequential addition of vanadyl sulfate to a phosphate-buffered solution of H2O2 released oxygen only after the second batch of vanadyl. Ethanol added to such reaction mixtures progressively decreased oxygen release and increased oxygen consumption during oxidation of vanadyl by H2O2. Inclusion of ethanol after any of the three batches of vanadyl resulted in varying amounts of oxygen consumption, a property also shared by other alcohols (methanol, propanol and octanol). On increasing the concentration of ethanol, vanadyl sulfate or H2O2, both oxygen consumption and acetaldehyde formation increased progressively. Formation of acetaldehyde decreased with increase in the ratio of vanadyl:H2O2 above 2:1 and was undetectable with ethanol at 0.1 mM. The reaction mixture which was acidic in the absence of phosphate buffer (pH 7.0), released oxygen immediately after the first addition of vanadyl and also in presence of ethanol soon after initial rapid consumption of oxygen, with no accompanying acetaldehyde formation. The results underscore the importance of some vanadium complexes formed during vanadyl oxidation in the accompanying oxygen-transfer reactions. 相似文献
54.
Roger F. Castilho Paulo C. Carvalho-Alves Anibal E. Vercesi Sérgio T. Ferreira 《Molecular and cellular biochemistry》1996,159(2):105-114
The major protein in the sarcoplasmic reticulum (SR) membrane is the Ca2+ transporting ATPase which carries out active Ca2+ pumping at the expense of ATP hydrolysis. The aim of this work was to elucidate the mechanisms by which oxidative stress induced by Fenton's reaction (Fe2+ + H2O2 HO· + OH–+ Fe3+) alters the function of SR. ATP hydrolysis by both SR vesicles (SRV) and purified ATPase was inhibited in a dose-dependent manner in the presence of 0–1.5 MM H2O2 plus 50 M Fe2+ and 6 mM ascorbate. Ca2+ uptake carried out by the Ca2+-ATPase in SRV was also inhibited in parallel. The inhibition of hydrolysis and Ca2+ uptake was not prevented by butylhydroxytoluene (BHT) at concentrations which significantly blocked formation of thiobarbituric acid-reactive substances (TBARS), suggesting that inhibition of the ATPase was not due to lipid peroxidation of the SR membrane. In addition, dithiothreitol (DTT) did not prevent inhibition of either ATPase activity or Ca2+ uptake, suggesting that inhibition was not related to oxidation of ATPase thiols. The passive efflux of 45Ca2+ from pre-loaded SR vesicles was greatly increased by oxidative stress and this effect could be only partially prevented (ca 20%) by addition of BHT or DTT. Trifluoperazine (which specifically binds to the Ca2+-ATPase, causing conformational changes in the enzyme) fully protected the ATPase activity against oxidative damage. These results suggest that the alterations in function observed upon oxidation of SRV are mainly due to direct effects on the Ca2+-ATPase. Electrophoretic analysis of oxidized Ca2+-ATPase revealed a decrease in intensity of the silver-stained 110 kDa Ca2+-ATPase band and the appearance of low molecular weight peptides (MW < 100 kDa) and high molecular weight protein aggregates. Presence of DTT during oxidation prevented the appearance of protein aggregates and caused a simultaneous increase in the amount of low molecular weight peptides. We propose that impairment of function of the Ca2+-pump may be related to aminoacid oxidation and fragmentation of the protein.Abbreviations AcP
acetylphosphate
- BHT
butylhydroxytoluene
- DTT
dithiothreitol
- Hepes
4-(2-hydroxyethyl)-1-piperazine-ethanesulfonic acid
- SDS
sodium dodecyl sulfate
- SDS-PAGE
polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate
- SR
sarcoplasmic reticulum
- SRV
sarcoplasmic reticulum vesicles
- TBA
thiobarbituric acid
- TBARS
thiobarbituric acid-reactive substances
- TFP
trifluoperazine 相似文献
55.
56.
Modeling the temperature response of nitrification 总被引:3,自引:2,他引:1
John M. Stark 《Biogeochemistry》1996,35(3):433-445
To model nitrification rates in soils, it is necessary to have equations that accurately describe the effect of environmental variables on nitrification rates. A variety of equations have been used previously to describe the effect of temperature on rates of microbial processes. It is not clear which of these best describes the influence of temperature on nitrification rates in soil. I compared five equations for describing the effects of temperature on nitrification in two soils with very different temperature optima from a California oak woodland-annual grassland. The most appropriate equation depended on the range of temperatures being evaluated. A generalized Poisson density function best described temperature effects on nitrification rates in both soils over the range of 5 to 50 °C; however, the Arrhenius equation best described temperature effects over the narrower range of soil temperatures that normally occurs in the ecosystem (5 to 28 °C). Temperature optima for nitrification in most of the soils were greater than even the highest soil temperatures recorded at the sites. A model accounting for increased maintenance energy requirements at higher temperatures demonstrates how net energy production, rather than the gross energy production from nitrification, is maximized during adaptation by nitrifier populations to soil temperatures. 相似文献
57.
Katsumi Mominoki Noriko Nakagawa-Tosa Masami Morimatsu Bunei Syuto Masayuki Saito 《Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology》1995,110(4):785-789
Haptoglobin (Hp), a hemoglobin-binding protein in plasma, consists of α and β subunits and has a tetra-chain arrangement (β-α-α-β) connected by disulfide bridges in most mammals so far examined. Dog Hp has been reported to be unique compared with other Hps in respect that (1) the two αβ units are joined by a non-covalent interaction rather than a disulfide bridge and (2) the α chain has an oligosaccharide-binding sequence (Asn-X-Ser/Thr) and is glycosylated. To determine whether the unique structures of dog Hp are common in the Carnivora, we purified Hps from sera of bear and cat, and analyzed their subunit structure and partial amino acid sequences. The analyses by gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, under both reducing and non-reducing conditions, revealed that bear and cat Hps have similar subunit arrangements to dog Hp, suggesting the absence of a disulfide bridge between two α chains. This was confirmed by amino acid sequence analysis of the α chains: that is, Cys15 participating in the inter-α chain disulfide bridge was replaced by Val in bear or Leu in cat and dog. Thus, the unique subunit arrangement of Hp reported in dog may be common in the Carnivora. In contrast to dog Hp, however, α chains of bear and cat Hps were found not to have the typical oligosaccharide binding sequence on their α chains and were not glycosylated. 相似文献
58.
The kinetics of oxidation and reduction of P700, plastocyanin, cytochrome f and cytochrome b-563 were studied in a reconstituted system consisting of Photosystem I particles, cytochrome bf complex and plastocyanin, all derived from pea leaf chloroplasts. Decyl plastoquinol was the reductant of the bf complex. Turnovers of the system were initiated by laser flashes. The reaction between oxidised P700 and plastocyanin was non-homogeneous in that a second-order rate coefficient of c. 5×10–7 M–1 s–1 applied to 80% of the P700+ and c. 0.7×107 M–1 s–1 to the remainder. In the presence of bf complex, but without quinol, the electron transfer between cytochrome f and oxidised plastocyanin could be described by a second-order rate coefficient of c. 4×107 M–1 s–1 (forward), and c. 1.6×107 M–1 s–1 (reverse). The equilibrium coefficient was thus 2.5. Unexpectedly, there was little reduction of cytochrome f
+ or plastocyanin+ by electrons from the Rieske centre. With added quinol, reduction of cytochrome b-563 occurred. Concomitantly, electrons appeared in the oxidised species. It was inferred that either the Rieske centre was not involved in the high-potential chain of electron transfer events, or that, only in the presence of quinol, electrons were quickly passed from the Rieske centre to cytochrome f
+. Additionally, the presence of quinol altered the equilibrium coefficient for the cyt f/PC interaction from 2.5 to c. 5. The reaction between quinol and the bf complex was describable by a second-order rate coefficient of about 3×106 M–1 s–1. The pattern of the redox reactions around the bf complex could be simulated in detail with a Q-cycle model as previously found for chloroplasts.Abbreviations AQS
anthraquinone sulphonate
- cyt
cytochrome
- cyt b-563(H)
high-potential cyt b-563
- cyt b-563(L)
low potential cyt b-563
- FeS(R)
the Rieske protein of the cyt bf complex, containing an Fe2S2 centre
- PC
plastocyanin
- PS
photosystem
- P700
reaction centre in PS I 相似文献
59.
K. Chandrasekhar A. Patricia Campbell Mei-Fen Jeng Arne Holmgren H. Jane Dyson 《Journal of biomolecular NMR》1994,4(3):411-432
Summary As a prelude to complete structure calculations of both the oxidized and reduced forms of Escherchia coli thioredoxin (Mr 11 700), we have analyzed the NMR data obtained for the two proteins under identical conditions. The complete aliphatic 13C assignments for both oxidized and reduced thioredoxin are reported. Correlations previously noted between 13C chemical shifts and secondary structure are confirmed in this work, and significant differences are observed in the C and C shifts between cis- and trans-proline, consistent with previous work that identifies this as a simple and unambiguous method of identifying cis-proline residues in proteins. Reduction of the disulfide bond in the active-site Cys32-Gly-Pro-Cys35 sequence causes changes in the 1H, 15N and 13C chemical shifts of residues close to the active site, some of them quite far distant in the amino acid sequence. Coupling constants, both backbone and side chain, show some differences between the two proteins, and the NOE connectivities and chemical shifts are consistent with small changes in the positions of several side chains, including the two tryptophan rings (Trp28 and Trp31). These results show that, consistent with the biochemical behavior of thioredoxin, there are minimal differences in backbone configuration between the oxidized and reduced forms of the protein. 相似文献
60.
Junichi Mano Kunio Kawamoto G. Charles Dismukes Kozi Asada 《Photosynthesis research》1993,38(3):433-440
A new binding site for anions which inhibit the water oxidizing complex (WOC) of Photosystem II in spinach has been identified. Anions which bind to this site inhibit the flash-induced S2/S0 catalase reaction (2H2O22H2O+O2) of the WOC by displacing hydrogen peroxide. Using a mass spectrometer and gas permeable membrane to detect the 32O2 product, the yield and lifetime of the active state of the flash-induced catalase (to be referred to simply as flash-catalase) reaction were measured after forming the S2 or S0-states by a short flash. The increase in flash-catalase activity with H2O2 concentration exhibits a Km=10–20 mM, and originates from an increase in the lifetime by 20-fold of the active state. The increased lifetime in the presence of peroxide is ascribed to formation of the long-lived S0-state at the expense of the unstable S2-state. The anion inhibition site differs from the chloride site involved in stimulating the photolytic water oxidation reaction (2H2OO2+4e-+4H+). Whereas water oxidation requires Cl- and is inhibited with increasing effectiveness by F-CN-N3
-, the flash-catalase reaction is weakly inhibited by Cl-, and with increasing effectiveness by F-CN-, N3
-. Unlike water oxidation, chloride is unable to suppress or reverse inhibition of the flash-catalase reaction caused by these anions. The inhibitor effectiveness correlates with the pKa of the conjugate acid, suggesting that the protonated species may be the active inhibitor. The reduced activity arises from a shortening of the lifetime of the flash-induced catalase active state by 3–10 fold owing to stronger anion binding in the flash-induced states, S2 and S0, than in the dark S-states, S1 and S-1. To account for the paradoxical result that higher anion concentrations are required to inhibit at lower H2O2 concentrations, where S2 forms initially after the flash, than at higher H2O2 concentrations, where S0 forms initially after the flash, stronger anion binding to the S0-state than to the S2-state is proposed. A kinetic model is given which accounts for these equilibria with anions and H2O2. The rate constant for the formation/release of O2 by reduction of S2 in the WOC is <0.4 s-1.Abbreviations ADRY
acceleration of the deactivation reactions of the water splitting enzyme system Y
- BTP
bis [tris(hydroxymethyl)methylamino]-propane
- CCCP
carbonylcyanide m-chlorophenylhyrazone
- DCBQ
2,5-dichlorobenzoquinone
- DMBQ
2,3-dimethylbenzoquinone
- WOC
water oxidizing complex 相似文献