首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 62 毫秒
1.
Bradyrhizobium japonicum utilizes cytochrome cbb 3 oxidase encoded by the fixNOQP operon to support microaerobic respiration under free-living and symbiotic conditions. It has been previously shown that, under denitrifying conditions, inactivation of the cycA gene encoding cytochrome c 550, the electron donor to the Cu-containing nitrite reductase, reduces cbb 3 expression. In order to establish the role of c 550 in electron transport to the cbb 3 oxidase, in this work, we have analyzed cbb 3 expression and activity in the cycA mutant grown under microaerobic or denitrifying conditions. Under denitrifying conditions, mutation of cycA had a negative effect on cytochrome c oxidase activity, heme c (FixP and FixO) and heme b cytochromes as well as expression of a fixP '–' lacZ fusion. Similarly, cbb 3 oxidase was expressed very weakly in a napC mutant lacking the c -type cytochrome, which transfers electrons to the NapAB structural subunit of the periplasmic nitrate reductase. These results suggest that a change in the electron flow through the denitrification pathway may affect the cellular redox state, leading to alterations in cbb 3 expression. In fact, levels of fixP '–' lacZ expression were largely dependent on the oxidized or reduced nature of the carbon source in the medium. Maximal expression observed in cells grown under denitrifying conditions with an oxidized carbon source required the regulatory protein RegR.  相似文献   

2.
Dark O2 consumption by the green alga Selenastrum minutum was sensitive to inhibition by the cytochrome pathway respiration inhibitor cyanide in the absence of an alternative oxidase inhibitor, consistent with previous work that suggested that this alga lacks alternative oxidase capacity. In contrast, addition of low concentrations of the cytochrome pathway inhibitor azide (50–750 μ M ) resulted in a stimulation of dark O2 consumption, while higher concentrations of azide (1–2 m M ) partially inhibited O2 consumption. Measurements of changes in cellular levels of pyruvate, malate and pyridine nucleotides upon cyanide addition were consistent with the absence of alternative oxidase capacity, and suggested that cyanide inhibition of O2 consumption was not due to nonspecific effects of cyanide. Addition of salicylhydroxamic acid (SHAM) also resulted in an increase in the rate of O2 consumption. Both azide- and SHAM-stimulated O2 consumption were sensitive to inhibition by 50 m M ascorbate or by cyanide. However, the ubiquinone analogs chloroquine and quinacrine specifically inhibited azide-stimulated O2 consumption, with only minor effects on SHAM-stimulated O2 consumption. These results suggest that azide-stimulated O2 consumption was not mediated by the previously characterized SHAM-stimulated oxidase, and are consistent with the possibility that azide-stimulated O2 consumption is mediated by a plasma membrane redox system.  相似文献   

3.
Abstract Washed cell suspensions of Crithidia oncopelti oxidizing a variety of substrates gave complex plots for the inhibition of respiration by potassium cyanide or azide. The data indicated the presence of at least two and possibly three terminal oxidases on the basis of their differential sensitivity to these inhibitors. The oxidase most sensitive to cyanide, azide and CO accounted for approx. 65–70% of whole cell respiration and is probably cytochrome oxidase a/a3. A second oxidase exhibiting low affinity for CO required high concentrations of KCN or azide for inhibition. This haemoprotein had the spectral characteristics of cytochrome o and accounted for 15–20% of cell respiration. Incomplete inhibition of respiration by high concentrations of KCN or azide suggested the presence of a third oxidase which was CO-unreactive.  相似文献   

4.
Phosphate addition to P-limited cells of Chlamydomonas reinhardtii resulted in an immediate increase in the rate of respiratory O2 consumption. The respiration rate continued to increase for several minutes after the addition of P1. Similar patterns of P1 stimulation of respiratory O2 consumption were observed in the presence of cyanide (cytochrome oxidase inhibitor) and propyl gallate (alternative oxidase inhibitor). Stimulation of O2 consumption was accompanied by rapid changes in levels of glycolytic intermediates. These changes were consistent with activation of ATP-dependent phosphofructokinase and pyruvate kinase. The adenylate pool exhibited only minor perturbations, P1, uptake resulted in extracellular acidification, which continued for several minutes after the exhaustion of added P1, whereas exhaustion of extracellular P1 resulted in a rapid decline in the O2 consumption rate. These results are consistent with control of respiration in P-limited cells occurring largely at the level of glycolysis.  相似文献   

5.
The unicellular green alga Chlamydomonas reinhardtii Dang. displays a high capacity for salicylhydroxamic acid (SHAM)—stimulated O2 consumption, mediated by extracellular peroxidaie. Addition of exogenous NADH also resulted in stimulation of O2 consumption. The SHAM-and NADH-stimulated peroxidase activity was partially sensitive to inhibition by exogenous superoxide dismutase, ascorbate, and gentisic acid. These compounds did not inhibit O2 consumption in the absence of effectors. SHAM-and NADH-stimulated peroxidase activity also was sensitive to inhibition by cyanide, and cyanide titration curves indicated that O2 consumption by peroxidase was more cyanide-sensitive than O2 consumption by cytochrome oxidase. The differential sensitivity to cyanide was used to estimate partitioning of O2 consumption between mitochondrial respiration and extracellular peroxidase. We suggest that, despite a large capacity for peroxidase-me-diated O2 consumption, peroxidase did not consume O2 at detectable rates in the absence of effectors. Therefore, in the absence of effectors, measured rates of O2 consumption represented the rate of mitochondrial respiration .  相似文献   

6.
Bean ( Phaseolus vulgaris L.) seedlings were cultured on complete or phosphate-deficient nutrient medium. After 14 days of culture on phosphate-deficient medium the visible symptoms of Pi deficiency were observed only in the shoot, the fresh and dry weights of the roots were slightly higher than in control plants. The decreased Pi content in the roots had little effect on total respiration rate but had an effect on the level of inhibition of respiration by cyanide. The high resistance of respiration to cyanide observed in Pi-deficient roots was the result of the suppression of cytochrome path activity and an increased participation of the alternative, cyanide-resistant pathway. The cytochrome pathway activity increased when inorganic phosphate was supplied to Pi-deficient roots for 1 or 3.5 h. It is speculated that the suppression of cytochrome pathway in Pi-deficient roots may result from restriction of the phosphorylating capacity or a partial inhibition of cytochrome oxidase activity.  相似文献   

7.
Abstract A cytochrome aa3 terminal oxidase was isolated from protoplast membrane vesicles of Micrococcus luteus grown under aerobic conditions. The purified complex showed similarities to cytochrome c oxidase (EC 1.9.3.1) of the electron transport chain of mitochondria and many prokaryotes. The enzyme was solubilized by subsequent treatment with the detergents CHAPS and n-dodecyl-β-d-maltoside and purified by ion-exchange chromatography using poly-L-lysine agarose and TMAE-fractogel-650 (S) columns, followed by hydroxyapatite chromatography. The purified complex is composed of two major subunits with apparent molecular masses of 54 and 32 kDa. After purification the isolated enzyme contains 12.1 nmol of heme A (mg protein)−1 and exhibits absorption maxima at 424 nm and 598 nm in the oxidized state and at 442 nm and 599 nm in the reduced state. The CO-difference spectrum shows peaks at 428 and 590 nm which is indicative of heme a 3, furthermore oxygen consumption was found to be sensitive to cyanide.  相似文献   

8.
Cells of the green alga Selenastrum minutum display a high capacity for extra-mitochondrial O2 consumption in the presence of effectors such as salicylhydroxamic acid and/or NADH. We provide evidence that this O2 consumption is mediated by extracellular peroxidase. Peroxidase capacity, measured as the potential for stimulation of O2 consumption by a combination of salicylhydroxamic acid and NADH, changed over a 10-day time course. Maximal stimulation of O2 consumption occurred at day three, at which point the capacity for peroxidase-mediated O2 consumption was three-to four-fold higher than that of the control O2 consumption rate. Peroxidase-mediated O2 consumption was sensitive to inhibition by 50 m M ascorbate and by cyanide. Cyanide titration curves indicated that O2 consumption by peroxidase was much more sensitive to inhibition by cyanide than was O2 consumption by cytochrome oxidase (I50 < 1.6 μ M and I50= 18.3 μ M cyanide, respectively). By using evidence from a combination of cyanide titration curves and ascorbate inhibition, we concluded that despite a large capacity for peroxidase-mediated O2 consumption, peroxidase did not measurably contribute to control rates of O2 consumption. In the absence of effectors, O2 consumption was mediated primarily by cytochrome oxidase.  相似文献   

9.
Abstract Membranes of the extremely thermoacidophilic archaeon Desulfurolobus ambivalens grown under aerobic conditions contain a quinol oxidase of the cytochrome aa 3-type as the most prominent hemoprotein. The partially purified enzyme consists of three polypeptide subunits with apparent molecular masses of 40, 27 and 20 kDa and contains two heme A molecules and one copper atom. CO difference spectra suggest one heme to be a heme a 3-centre. The EPR spectra indicate the presence of a low-spin and a high-spin heme species. Redox titrations of the solubilized enzyme show the presence of two reduction processes, with apparent potentials of + 235 and + 330 mV. The enzyme cannot oxidize reduced cytochrome c , but rather serves as an oxidase of caldariella quinone. Due to their very simple composition, D . ambivalens cell appear as a promising candidate to study Structure-function relationships of cytochrome aa 3 in the integral membrane state.  相似文献   

10.
Irradiation of starved cultures of Saccharomyces cerevisiae with blue light under aerobic conditions inhibited the capacity of the yeast cells to respire added substrates (e.g., ethanol) and stimulated endogenous respiration. Spectroscopic examination of the cells showed that the irradiation destroyed both cytochrome a and a3 components of cytochrome oxidase and a part of the cytochrome b. Irradiation under anaerobic conditions had no effect on the respiratory capacity or the cytochrome content of the cells. Under aerobic conditions cytochrome a3 was protected against photodestruction when complexed with cyanide and cytochrome a was protected when complexed with azide.  相似文献   

11.
Abstract The midpoint redox potentials (E'0) of the cytochromes of Pseudomonas carboxydovorans have been studied by means of coupled spectrum deconvolution and potentiometric analysis. Membranes of cells grown on different substrates (CO; H2+ CO2; or pyruvate) contained cytochromes with similar absorption peaks and redox potentials. The cytochromes of the CO-sensitive main electron pathway of the respiratory chain revealed redox potentials in the same range as mitochondrial cytochromes (cytochrome b -555, about −20 mV; cytochrome c and cytochrome a , about +220 mV). For the cytochromes of the CO-insensitive alternative electron pathway, which allows uninhibited growth and respiration in the presence of high concentrations of CO, redox potentials of approx. +50 mV (cytochrome b -558) and −11 to −215 mV (cytochrome b -561) were determined. Cytochrome [ib-561], earlier proposed as the alternative terminal oxidase o in this organism, was shown to possess the lowest half reduction potential of all the cytochromes present in the cells. Measurements of the apparent K m value for oxygen revealed a low affinity of cytochrome a ( K m/ 5 υ M O2) and a very high affinity of the CO-insensitive oxidase ( K m < 0.5 μ M O2). The high affinity to oxygen might be responsible for the CO-insensitivity of this unusual cytochrome o .  相似文献   

12.
Abstract The role of cytochrome b 562, a fragile constituent of the respiratory terminal oxidase supercomplex of the thermoacidophilic archaeon, Sulfolobus sp. strain 7, was investigated spectroscopically in the membrane-bound state. Cytochrome b 562 did not react with CO or cyanide in the membrane-bound state, while it was irreversibly modified to a CO-reactive form ( b 562) upon solubilization in the presence of cholate and LiCl. Cyanide titration analyses with the succinate-reduced membrane suggested that cytochrome b 562 was upstream of both the ' g y= 1.89' Rieske FeS cluster and the a -type cytochromes. These results show that the b -type cytochrome functions as an intermediate electron transmitter in the terminal oxidase supercomplex.  相似文献   

13.
14CO2 evolution of prelabeled Scenedesmus obliquus Kütz, has been followed in the dark and in the light. In the light, no carbon dioxide is evolved. Addition of unlabeled NaHCO, leads to 14CO2 release attaining 20 to 30% of the dark rate. Double-reciprocal plots of NaHCO3 concentrations vs 14CO2 release results in a straight line, indicative of competition between exogenously supplied bicarbonate and endogenously evolved carbon dioxide. With this method, it is possible to measure CO2 evolved by respiration in the light and to show that true photoinhibition of respiration occurs in Scenedesmus . In the light. DCMU substantially increases 14CO2 evolution; in the presence of the uncoupler carbonyl cyanide- m -chlorophenylhydrazone. 14CO2 evolution is comparable to that in the dark. 14CO2 release and oxygen uptake in the dark are only slightly affected by cyanide, indicative of a cyanide-resistant respiration and/or fermentation as the essential CO2-yielding processes in the presence of cyanide. These results, compared with concurrent ATP levels, lead us to assume that energy charge is not the only factor responsible for photoinhibition of respiration.  相似文献   

14.
Abstract The in situ method for determination of reduction levels of cytochromes b and c pools during steady-state growth (Pronk et al., Anal. Biochem. 214, 149–155, 1993) was applied to chemostat cultures of the wild-type, a cytochrome aa3 single mutant and a cytochrome aa3/d double mutant of Azorhizobium caulinodans . For growth with NH4+ as the N source, the results indicate that (i) the aa3 mutant strains growing at a dissolved O2 tension of 0.5% possess an active alternative cytochrome c oxidase, which is hardly present during fully aerobic growth, and assuming that (i) also pertains to the wild-type, (ii) the wild-type uses cytochrome aa3 under fully aerobic conditions. For growth with N2 as the N source, it was found that the aa3 mutant strains growing at dissolved O2 tensions ranging from 0.5 to 3.0% also contain an active alternative cytochrome c oxidase.  相似文献   

15.
We tested the hypotheses that relative activity of the less efficient alternative oxidase (AOX) path changes with diurnal temperature changes, and thus changes carbon use efficiency with temperature. The activities of the alternative and cytochrome oxidase (COX) paths in plant tissues of three species were determined by measuring 18O/16O discrimination and total respiration from 17 to 36 °C. A new, more accurate method for calculating oxygen uptake rate from the mass spectrometry data was developed. Total carbon use efficiency was calculated from the ratio of respiratory heat and CO2 rates measured from 10 to 35 °C. Oxygen isotope discrimination (22.9 ± 0.4‰) and AOX participation were invariant with temperature in leaf tissue of Cucurbita pepo , Nicotiana sativa and Vicia faba , thus falsifying the first part of the hypothesis. Stress responses of respiration at the temperature extremes limited the range for which carbon use efficiency could be accurately measured to 15–30 °C in N. sativa , to 10–25 °C in C. pepo and to 20–30 °C in V. faba . Carbon-use efficiency was invariant at these temperatures in these species, demonstrating that changes in other pathways that would vary carbon-use efficiency were also invariant with temperature.  相似文献   

16.
The activity of the alternative path of O2 consumption in detached and intact roots of barley [ Hordeum distichum (L.) Lam. cv. Maris Mink] was determined by titration with salicylhydroxamic acid (SHAM) in the presence and absence of cyanide. In the absence of cyanide, only high concentrations were inhibititory (> 5 m M ). whilst in its presence low SHAM concentrations (2.5–5.0 m M ) gave maximum inhibition: the resulting ϱ Valt plots were non-linear. A SHAM-stimulated peroxidase could readily be washed from these roots, but non-linearity cannot be explained in terms of SHAM-stimulation of this peroxidase as it is not active in the absence of an exogenous supply of NADH. In detached roots the degree of inhibition of respiration with 25 m M SHAM was nearly double the capacity of the alternative path (measured as the degree of inhibition by SHAM in the presence of cyanide), suggesting non-specific inhibition. Effects of SHAM on cytochrome path activity in intact roots were examined by reverse titration with cyanide in the presence and absence of SHAM. At 5 m M SHAM had no effect on the cytochrome path, but at 25 m M it inhibited. We conclude that the only factor causing non-linearity of ϱValt plots in barley roots is non-specific inhibition of the cytochrome path by high concentrations of SHAM; consequently only low concentrations of SHAM (2.5–5.0 m M ) are suitable for estimating alternative path activity in barley roots.  相似文献   

17.
The role of mitochondrial respiration in optimizing photosynthesis was assessed in mesophyll protoplasts of pea ( Pisum sativum L., cv. Arkel) by using low concentrations of oligomycin (an inhibitor of oxidative phosphorylation), antimycin A (inhibits cytochrome pathway of electron transport) and salicylhydroxamic acid (SHAM, an inhibitor of alternative oxidase). All three compounds decreased the rate of photosynthetic O2 evolution in mesophyll protoplasts, but did not affect chloroplast photosynthesis. The inhibition of photosynthesis by these mitochondrial inhibitors was stronger at optimal CO2 (1.0 m M NaHCO3) than that at limiting CO2 (0.1 m M NaHCO3). We conclude that mitochondrial metabolism through both cytochrome and alternative pathways is essential for optimizing photosynthesis at limiting as well as at optimal CO2. The ratios of ATP to ADP in whole protoplast extracts were hardly affected, despite the marked decrease in their photosynthetic rates by SHAM. Similarly, the decrease in the ATP/ADP ratio by oligomycin or antimycin A was more pronounced at limiting CO2 than at optimal CO2. The mitochondrial oxidative electron transport, through both cytochrome and alternative pathways, therefore akppears to be more important than oxidative phosphorylation in optimizing photosynthesis, particularly at limiting CO2 (when ATP demand is expected to be low). Our results also confirm that the alternative pathway has a significant role in contributing to the cellular ATP, when the cytochrome pathway is limited.  相似文献   

18.
We showed that temperature responses of dark respiration for foliage of Pinus radiata could be approximated by Arrhenius kinetics, whereby E 0 determines shape of the exponential response and denotes overall activation energy of respiratory metabolism. Reproducible and predictable deviation from strict Arrhenius kinetics depended on foliage age, and differed between R CO2 and R O2. Inhibition of oxygen reduction ( R O2) by cyanide (inhibiting COX) or SHAM (inhibiting AOX) resulted in reproducible changes of the temperature sensitivity for R O2, but did not affect R CO2. Enthalpic growth – preservation of electrons in anabolic products – could be approximated with knowledge of four variables: activation energies ( E 0) for both R CO2 and R O2, and basal rates of respiration at a low reference temperature ( R REF). Rates of enthalpic growth by P. radiata needles were large in spring due to differences between R REF of oxidative decarboxylation and that of oxygen reduction, while overall activation energies for the two processes were similar. Later during needle development, enthalpic growth was dependent on differences between E 0 for R CO2 as compared with R O2, and increased E 0( R O2) indicated greater contributions of cytochrome oxidase to accompany the switch from carbohydrate sink to source. Temperature-dependent increments in stored energy can be calculated as the difference between R CO2▵ H CO2 and R O2▵ H O2.  相似文献   

19.
Abstract. Oxygen uptake characteristics of the roots of three Rumex species were compared, and related to kinetics of the respiratory system and to root anatomy. The observed differences could not be explained by differences in fundamental characteristics of the oxygen uptake system: with all three species, cytochrome-mediated respiration contributed 70% and cyanide-insensitive (alternative) respiration 30% of the total respiration rate, and apparent Km values of cytochrome oxidase were lower than those obtained for the alternative oxidase in all cases. However, differences in critical oxygen pressure for respiration (COPR) and in apparent Km for oxygen, were strongly correlated with differences in root porosity and root diameter. Km(O2) values at high and low temperatures were determined, and from Arrhenius plots of oxygen uptake rates between 11 and 32°C, the role of diffusional impedance could be estimated. Root respiration of Rumex maritimus and R. crispus , both with high root porosity, but differing in root diameter, had a low Km for oxygen (3–7 mmol m−3). In contrast with this were the responses of R. thvrsiflorus , which has thin roots but low root porosity: a high Km (10-20 mmol m−3) was found at all temperatures. The role of diffusional impedance as a function of temperature in oxygen uptake rate by the three species is discussed and related to the differential resistance of the species towards flooding.  相似文献   

20.
The regularity of appearance of cyanide-resistant respiration and cytochrome d in various bacteria as well as the relationship between the degree of resistance of respiration to cyanide and cytochrome d content was studied. Bacteria able to synthesize cyanide-resistant respiration were shown to appear during transition of culture to the stationary phase of growth caused by the exhaustion of carbon source. No regulatory of appearance of cytochrome d was observed. There is no correlation between the degree of resistance to cyanide and cytochrome d content. It was concluded that the cyanide-resistant respiration of bacteria and eukaryotic microorganisms may be associated with the functioning of a non-cytochrome nature oxidase.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号