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21.
Sudha Rao Gopalakrishna Kamath Gururaj Maralihalli Anil S. Bhagwat 《Photosynthesis research》1987,12(2):155-164
The -aminolevulinic acid dehydratase activity was irreversibly inactivated by irradiation of the enzyme in presence of flavin mononucleotide. The loss of enzyme activity was dependent on time of irradiation, concentration of FMN and intensity of irradiance. It required oxygen and was markedly enhanced in heavy water. The presence of levulinic acid (a competitive inhibitor of -ALAD) during irradiation prevented the inactivation considerably indicating photooxidative damage at or near the active site. Superoxide dismutase, sodium benzoate and sodium formate offered no protection, but singlet oxygen quenchers like azide and tryptophan were effective. NADH, electron donor to excited flavins, also prevented the loss of enzyme activity. These results indicate that singlet oxygen produced by light absorption of FMN was responsible for the photooxidative inhibition of the enzyme.Abbreviations ALAD
-aminolevulinic acid dehydratase
- FMN
flavin mononucleotide
- O2
-
superoxide
- H2O2
hydrogen peroxide
- 102
singlet oxygen
- LA
levulinic acid
- PBG
porphobilinogen
- BSA
bovine serum albumin
- BME
2-mercaptoethanol
- SOD
superoxide dismutase
- pHMB
para-hydroxymercuribenzoate
- DTT
dithiothreitol
- FAD
flavin adenine dinucleotide
- NADH
nicotinamide adenine dinucleotide 相似文献
22.
A stable carbon isotope study of dissolved inorganic carbon cycling in a softwater lake 总被引:3,自引:0,他引:3
Andrew L. Herczeg 《Biogeochemistry》1987,4(3):231-263
The dissolved inorganic carbon (DIC) cycle in a softwater lake was studied using natural variations of the stable isotopes of carbon,12C and13C. During summer stratification there was a progressive decrease in epilimnion DIC concentration with a concomitant increase in 13CDIC), due to preferential uptake of12C by phytoplankton and a change in the dominant CO2 source from inflow andin situ oxidation to invasion from the atmosphere. There was an increase in hypolimnion DIC concentration throughout summer with a concomitant general decrease in 13CDIC from oxidation of the isotopically light particulate organic carbon that sank down through the thermocline from the epilimnion.Mass balance calculations of DI12C and DI13C in the epilimnion for the summer (June 23–September 25) yield a mean rate of net conversion of DIC to organic carbon (Corg) of 430 ± 150 moles d-1 (6.5 ± 1.8 m moles m-2 d-1. Net CO2 invasion from the atmosphere was 420 ± 120 moles d-1 (6.2 ± 1.8 m moles m-2 d-1) with an exchange coefficient of 0.6 ± 0.3m d-1. These results imply that at least for the summer months the phytoplankton obtained about 90% of their carbon from atmosphere CO2. About 50% of CO2 invasion and conversion to Corg for the summer occurred during a two week interval in mid-summer.DIC concentration increased in the hypolimnion at a rate of 350 ± 70 moles DIC d-1 during summer stratification. The amount of DIC added to the hypolimnion was equivalent to 75 ± 20% of net conversion of DIC to Corg in the euphotic zone over spring and summer implying rapid degradation of POC in the hypolimnion. The 13C of DIC added to the deep water (-22.) was too heavy to have been derived from oxidation of particulate organic carbon alone. About 20% of the added DIC must have diffused from hypolimnetic sediments where relatively heavy CO2 (-7) was produced by a combination of POC oxidation and as a by-product of methanogenesis. 相似文献
23.
A. Tyagi J. Hermans J. Steppuhn Ch. Jansson F. Vater R. G. Herrmann 《Molecular & general genetics : MGG》1987,207(2-3):288-293
Summary Several cDNA clones encoding the 33 kDa protein associated with the photosynthetic water oxidation activity of spinach were sequenced. A 1208 bp insert of one of the clones encodes the entire 331 amino acid residues of the precursor protein including 84 amino acids (8.5 kDa) of the amino-terminal transit peptide, 49 bp of the 5 and 111 bp of the 3 untranslated segment of the mRNA. The 3 poly(A) tail starts 19 bp downstream from a putative polyadenylation signal, TATAAA. The hydrophilic mature protein consists of 247 amino acid residues corresponding to an Mr of 26.5 kDa, which is 6.5 kDa smaller than the value determined by SDS-polyacrylamide gel electrophoresis (33–34 kDa), and shows a certain degree of conservation with the putative Mn-complexing active sites of bacterial Mn-dependent superoxide dismutases. The anatomy of the unusually long transit sequence is discussed with regard to current concepts of protein import into and protein routein within the organelle. 相似文献
24.
When detergent-derived photosystem II (PSII) membranes are treated with CaCl2 to remove the three extrinsic proteins associated with the O2-evolving complex, the resulting membranes (CaPSII) can still catalyze water oxidation if sufficient Ca2+ and Cl- are present. When CaPSII membranes are exposed to single turnover flashes on an O2 rate electrode, anomalous O2 is produced by the first two flashes. The addition of catalase to the membrane suspension completely inhibits O2 produced by the first two flashes, but not by subsequent flashes. Exogenous H2O2 stimulates anomalous O2 production by the first few flashes in CaPSII membranes, but not in control PSII membranes. Diuron (DCMU) does not inhibit H2O2-stimulated O2 production by the first flash. However, it does inhibit the O2 yield of all subsequent flashes, indicating that all flash-induced O2 signals in CaPSII membranes are dependent on photosystem II electron transport. H2O2 stimulation of O2 yields is inhibited in Tris-, heat-, and EDTA-(ethylenediaminetetraacetic acid)-treated CaPSII. In the presence of high salt, H2O2 (but not EDTA) treatment of CaPSII, extracts Mn functional in normal photosynthetic O2 evolution. The addition of exogenous Mn2+ reconstitutes anomalous O2 production in Tris-and H2O2/EDTA-treated CaPSII preparations but only in the presence of H2O2. Anomalous H2O2-stimulated O2 production can be observed both with a Clark electrode (steady state) and an O2 rate electrode (flash sequence). The mechanism involves electron donation from H2O2, mediated by free Mn2+, to PSII, and the 33-kDa extrinsic protein under some conditions can block this process. Since H2O2 can remove functional Mn from CaPSII membranes, its presence can convert functional Mn to the Mn2+ mediator state required for anomalous O2 production. EDTA binds Mn in CaPSII disrupted by H2O2 and prevents anomalous O2 evolution.Abbreviations CaPSII
a PSII preparation washed with approximately 1M CaCl2
- Chl
chlorophyll
- DCBQ
2,6-dichloro-p-benzoquinone
- DCMU (diuron)
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- EDTA
ethylenediaminetetraacetic acid
- MES
2-[N-morpholino]-ethanesulfonic acid
- PSII
a detergent-derived photosystem II membrane preparation
- RC
reaction center
- Tris
tris(hydroxymethyl)-aminomethane
- Yn
oxygen rate electrode flash yield resulting from the nth flash of a sequence of single turnover flashes of light
Operated by the Midwest Research Institute for the U.S. Department of Energy under contract DE-AC02-83CH10093. 相似文献
25.
本实验在14只麻醉开胸狗心脏上观察了氟碳乳剂与右旋糖酐稀释血液对心肌耗氧量与供应缺血心肌氧量关系的影响。以左室压力-时间指数(SPTI)作为心肌耗氧量的指标,根据冠脉有效侧支血流量(ECF)、PaO_2和 Hb 浓度计算供应缺血心肌的氧量。实验结果表明,低分子右旋糖酐稀释血液后,SPTI 暂时性轻度增加(稀释后30min 时较对照增加7.1±2.7%,P<0.05,稀释后60min 时增加2.8±1.2%,P>0.05),ECF 明显增多(稀释后30min 时较对照增加58.5±6.1%,P<0.01),缺血区边缘心肌氧供需关系未发生明显变化。氟碳乳剂稀释血液后,SPTI 的变化规律与右旋糖酐稀释后相同(稀释后30min 和60min 时分别较对照增加2.5±0.7%和1.9±0.8%)ECF 和 PaO_2升高(稀释后30min 时分别较对照增加53.9±6.7%和93±8.9%),供应缺血心肌的氧量显著增加,缺血区边缘心肌氧供需矛盾明显改善。 相似文献
26.
We have shown, in a preliminary report, that macrophages can induce strand breaks in the DNA of co-cultured tumor cells (Chong et al., 1988). The present study is designed to determine if oxygen-centered species generated by the cell-free enzyme-substrate combination of hypoxanthine and xanthine oxidase can induce similar lesions and to identify the specific mediator(s). We report that co-incubation of murine mammary tumor cell lines with hypoxanthine and xanthine oxidase leads to the induction of DNA-strand breaks as determined by fluorescence analysis of DNA unwinding (FADU) assay or alkaline elution techniques. This damage is preventable by catalase which removes hydrogen peroxide but no protection is provided by agents to remove or prevent the formation of superoxide anion (superoxide dismutase), or hydroxyl radical (mannitol or the iron chelator o-phenanthroline). Likewise, cyclooxygenase or lipoxygenase inhibitors of arachidonate metabolism (indomethacin, nordihydroguaiaretic acid, caffeic acid) or bromophenacyl bromide do not alter the degree of DNA scission. Treatment with higher doses of oxygen species leads to significant toxicity as determined by evaluation of cell growth potential or colony-forming ability. Again, toxicity is prevented only by the presence of catalase. Tumor cells are able to rejoin strand breaks at lower, less toxic doses. When comparing different tumor cell subpopulations at various stages of progression, i.e., metastatic vs. nonmetastatic, for sensitivity to hydrogen peroxide-induced strand breakage, we found that at lower concentrations (less than 5μM) metastatic populations are sensitive whereas nonmetastatic populations exhibit no significant breakage. At higher concentrations of hydrogen peroxide, all lines were sensitive, suggesting that a lower threshold of sensitivity may exist for more progressed tumour cell lines. 相似文献
27.
In vivo effect of abscisic acid (ABA) on photosynthetic oxygen evolution was investigated in barley chloroplasts. The most important kinetic parameters of O2-producing reactions were changed. The results show inhibition of the O2-flash yields at ABA concentrations of 10 mol/l and 100 mol/l and an increase in the degree of damping of the oscillations. ABA has a marked effect on the distribution of the oxygenevolving centers in S0 and S1 states and on sum of the centers (S0+S1) estimated according to the Kok model. In addition, the amplitude and the shape of the initial oxygen burst under continuous illumination are also significantly altered. At a concentration of 100 mol/l, ABA strongly inhibits Hill reaction activity measured by DCPIP reduction. The results cannot be explained by the hypothesis of socalled stomata effect. On the other hand, no effects were observed on the investigated parameters in experiments involving ABA applied in vitro to isolated chloroplasts. It is hypothesized that ABA disrupts the granal chloroplasts structure and raises the degree of participation of the cooperative mechanism of O2-evolution connected with the functioning of PS II centers in the stroma situated thylakoids.Abbreviations DCPIP
2,6-Dichlorophenolindophenol
- DCMU
3-(3,4-dichlorophenil)-1,1-dimethylurea
- HEPES
N-2-Hydroxyethylpiperazine-N-2-ethane sulfonic acid
- PSII
photosystem II
- RubisCO
Ribulose-1,5-bis-phosphate carboxylase-oxygenase 相似文献
28.
Curtis W. Hoganson Demetrios F. Ghanotakis Gerald T. Babcock Charles F. Yocum 《Photosynthesis research》1989,22(3):285-293
Manganese in the oxygen-evolving complex is a physiological electron donor to Photosystem II. PS II depleted of manganese may oxidize exogenous reductants including benzidine and Mn2+. Using flash photolysis with electron spin resonance detection, we examined the room-temperature reaction kinetics of these reductants with Yz
+, the tyrosine radical formed in PS II membranes under illumination. Kinetics were measured with membranes that did or did not contain the 33 kDa extrinsic polypeptide of PS II, whose presence had no effect on the reaction kinetics with either reductant. The rate of Yz
+ reduction by benzidine was a linear function of benzidine concentration. The rate of Yz
+ reduction by Mn2+ at pH 6 increased linearly at low Mn2+ concentrations and reached a maximum at the Mn2+ concentrations equal to several times the reaction center concentration. The rate was inhibited by K+, Ca2+ and Mg2+. These data are described by a model in which negative charge on the membrane causes a local increase in the cation concentration. The rate of Yz
+ reduction at pH 7.5 was biphasic with a fast 400 s phase that suggests binding of Mn2+ near Yz
+ at a site that may be one of the native manganese binding sites.Abbreviations PS II
Photosystem II
- YD
tyrosine residue in Photosystem II that gives rise to the stable Signal II EPR spectrum
- Yz
tyrosine residue in Photosystem II that mediates electron transfer between the reaction center chlorophyll and the site of water oxidation
- ESR
electron spin resonance
- DPC
diphenylcarbazide
- DCIP
dichlorophenolindophenol 相似文献
29.
Jawahar Kalra Dave Lautner K. Lorne Massey Kailash Prasad 《Molecular and cellular biochemistry》1988,84(2):233-238
Summary The effect of oxygen free radicals, generated by xanthine and xanthine oxidase, was studied on the release of lysosomal hydrolase from rat liver lysosomes in vitro. A lysosomal enriched subcellular fraction was prepared, using differential centrifugation technique, from the homogenate of rat liver. The biochemical purity of the lysosomal fraction was established by using the markers of different cellular organelles. Oxygen free radicals were generated in vitro by the addition of xanthine and xanthine oxidase. The release of lysosomal hydrolase (-glucuronidase) from the lysosomal fraction was measured. There was a 3 to 4 fold increase in the release of -glucuronidase activity in the presence of xanthine and xanthine oxidase when compared to that in the absence of xanthine and xanthine oxidase. In the presence of superoxide dismutase (SOD), a scavenger of oxygen free radicals, the xanthine and xanthine oxidase system was unable to induce the release of -glucuronidase activity from the lysosomes. Sonication (2 bursts for 15 sec each) and Lubrol (2 mg/10 mg lysosomal protein) treatment, which are known to cause membrane disruption, also induced the release of -glucuronidase from lysosomal fraction. This release of -glucuronidase by sonication and lubrol treatment was not prevented by SOD. These data indicate that lysosomal disruption is a consequence of oxygen free radicals, generated by xanthine and xanthine oxidase.Abbreviations HEPES
N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid
- EGTA
Ethylene Glycol Bis-(-aminoethyl ether)N,N,-N,N-tetracetic acid
- Tris
Tris (hydroxymethyl) aminomethane
- SOD
Superoxide Dismutase 相似文献
30.
A role for haemoglobin in all plant roots? 总被引:4,自引:2,他引:2
Abstract. We have found haemoglobin in plant roots whereas previously it has been recorded only in nitrogen fixing nodules of plants. Haemoglobin occurs not only in the roots of those plants that are capable of nodulation but also in the roots of species that are not known to nodulate. We suggest that a haemoglobin gene may be a component of the genome of all plants. The gene structure and sequence in two unrelated families of plants suggests that the plant haemoglobins have had a single origin and that this origin relates to the haemoglobin gene of the animal kingdom. At present we cannot completely rule out the possibility of a horizontal transfer of the gene from the animal kingdom to a progenitor of the dicotyledonous angiosperms but we favour a single origin of the gene from a progenitor organism to both the plant and animal kingdoms. We speculate about the possible functions of haemoglobin in plant roots and put the case that it is unlikely to have a function in facilitating oxygen diffusion. We suggest that haemoglobin may act as a signal molecule indicating oxygen deficit and the consequent need to shift plant metabolism from an oxidative to a fermentative pathway of energy generation. 相似文献