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 546 毫秒
1.
《BBA》2006,1757(9-10):1133-1143
In cytochrome c oxidase, oxido-reductions of heme a/CuA and heme a3/CuB are cooperatively linked to proton transfer at acid/base groups in the enzyme. H+/e cooperative linkage at Fea3/CuB is envisaged to be involved in proton pump mechanisms confined to the binuclear center. Models have also been proposed which involve a role in proton pumping of cooperative H+/e linkage at heme a (and CuA). Observations will be presented on: (i) proton consumption in the reduction of molecular oxygen to H2O in soluble bovine heart cytochrome c oxidase; (ii) proton release/uptake associated with anaerobic oxidation/reduction of heme a/CuA and heme a3/CuB in the soluble oxidase; (iii) H+ release in the external phase (i.e. H+ pumping) associated with the oxidative (R  O transition), reductive (O  R transition) and a full catalytic cycle (R  O  R transition) of membrane-reconstituted cytochrome c oxidase. A model is presented in which cooperative H+/e linkage at heme a/CuA and heme a3/CuB with acid/base clusters, C1 and C2 respectively, and protonmotive steps of the reduction of O2 to water are involved in proton pumping.  相似文献   

2.
Proton pumping heme-copper oxidases represent the terminal, energy-transfer enzymes of respiratory chains in prokaryotes and eukaryotes. The CuB-heme a3 (or heme o) binuclear center, associated with the largest subunit I of cytochrome c and quinol oxidases, is directly involved in the coupling between dioxygen reduction and proton pumping. The role of the other subunits is less clear. The following aspects will be covered in this paper:i) the efficiency of coupling in the mitochondrial aa3 cytochrome c oxidase. In particular, the effect of respiratory rate and protonmotive force on the H+/e? stoichiometry and the role of subunit IV; ii) mutational analysis of the aa3 quinol oxidase of Bacillus subtilis addressed to the role of subunit III, subunit IV and specific residues in subunit I; iii) possible models of the protonmotive catalytic cycle at the binuclear center. The observations available suggest that H+/e?coupling is based on the combination of protonmotive redox catalysis at the binuclear center and co-operative proton transfer in the protein.  相似文献   

3.
The dioxygen reduction mechanism in cytochrome oxidases relies on proton control of the electron transfer events that drive the process. Proton delivery and proton channels in the protein that are relevant to substrate reduction and proton pumping are considered, and the current status of this area is summarized. We propose a mechanism in which the coupling of the oxygen reduction chemistry to proton translocation (P  F transition) is related to the properties of two groups of highly conserved residues, namely, His411/G386-T389 and the heme a3–propionateA–D399–H403 chain. This article is part of a Special Issue entitled: Respiratory Oxidases.  相似文献   

4.
The respiratory heme-copper oxidases catalyze reduction of O2 to H2O, linking this process to transmembrane proton pumping. These oxidases have been classified according to the architecture, location and number of proton pathways. Most structural and functional studies to date have been performed on the A-class oxidases, which includes those that are found in the inner mitochondrial membrane and bacteria such as Rhodobacter sphaeroides and Paracoccus denitrificans (aa3-type oxidases in these bacteria). These oxidases pump protons with a stoichiometry of one proton per electron transferred to the catalytic site. The bacterial A-class oxidases use two proton pathways (denoted by letters D and K, respectively), for the transfer of protons to the catalytic site, and protons that are pumped across the membrane. The B-type oxidases such as, for example, the ba3 oxidase from Thermus thermophilus, pump protons with a lower stoichiometry of 0.5 H+/electron and use only one proton pathway for the transfer of all protons. This pathway overlaps in space with the K pathway in the A class oxidases without showing any sequence homology though. Here, we review the functional properties of the A- and the B-class ba3 oxidases with a focus on mechanisms of proton transfer and pumping. This article is part of a Special Issue entitled: Respiratory Oxidases.  相似文献   

5.
Cytochrome ba3 (ba3) of Thermus thermophilus (T. thermophilus) is a member of the heme–copper oxidase family, which has a binuclear catalytic center comprised of a heme (heme a3) and a copper (CuB). The heme–copper oxidases generally catalyze the four electron reduction of molecular oxygen in a sequence involving several intermediates. We have investigated the reaction of the fully reduced ba3 with O2 using stopped-flow techniques. Transient visible absorption spectra indicated that a fraction of the enzyme decayed to the oxidized state within the dead time (~ 1 ms) of the stopped-flow instrument, while the remaining amount was in a reduced state that decayed slowly (k = 400 s? 1) to the oxidized state without accumulation of detectable intermediates. Furthermore, no accumulation of intermediate species at 1 ms was detected in time resolved resonance Raman measurements of the reaction. These findings suggest that O2 binds rapidly to heme a3 in one fraction of the enzyme and progresses to the oxidized state. In the other fraction of the enzyme, O2 binds transiently to a trap, likely CuB, prior to its migration to heme a3 for the oxidative reaction, highlighting the critical role of CuB in regulating the oxygen reaction kinetics in the oxidase superfamily. This article is part of a Special Issue entitled: Respiratory Oxidases.  相似文献   

6.
A combined DFT/electrostatic approach is employed to study the coupling of proton and electron transfer reactions in cytochrome c oxidase (CcO) and its proton pumping mechanism. The coupling of the chemical proton to the internal electron transfer within the binuclear center is examined for the O  E transition. The novel features of the His291 pumping model are proposed, which involve timely well-synchronized sequence of the proton-coupled electron transfer reactions. The obtained pKas and Ems of the key ionizable and redox-active groups at the different stages of the O  E transition are consistent with available experimental data. The PT step from E242 to H291 is examined in detail for various redox states of the hemes and various conformations of E242 side-chain. Redox potential calculations of the successive steps in the reaction cycle during the O  E transition are able to explain a cascade of equilibria between the different intermediate states and electron redistribution between the metal centers during the course of the catalytic activity. All four electrometric phases are discussed in the light of the obtained results, providing a robust support for the His291 model of proton pumping in CcO. This article is part of a Special Issue entitled: Respiratory oxidases.  相似文献   

7.
The reactions of molecular oxygen (O2) and nitric oxide (NO) with reduced Thermus thermophilus (Tt) ba3 and bovine heart aa3 were investigated by time-resolved optical absorption spectroscopy to establish possible relationships between the structural diversity of these enzymes and their reaction dynamics. To determine whether the photodissociated carbon monoxide (CO) in the CO flow-flash experiment affects the ligand binding dynamics, we monitored the reactions in the absence and presence of CO using photolabile O2 and NO complexes. The binding of O2/NO to reduced ba3 in the absence of CO occurs with a second-order rate constant of 1 × 109 M? 1 s? 1. This rate is 10-times faster than for the mammalian enzyme, and which is attributed to structural differences in the ligand channels of the two enzymes. Moreover, the O2/NO binding in ba3 is 10-times slower in the presence of the photodissociated CO while the rates are the same for the bovine enzyme. This indicates that the photodissociated CO directly or indirectly impedes O2 and NO access to the active site in Tt ba3, and that traditional CO flow-flash experiments do not accurately reflect the O2 and NO binding kinetics in ba3. We suggest that in ba3 the binding of O2 (NO) to heme a32 + causes rapid dissociation of CO from CuB+ through steric or electronic effects or, alternatively, that the photodissociated CO does not bind to CuB+. These findings indicate that structural differences between Tt ba3 and the bovine aa3 enzyme are tightly linked to mechanistic differences in the functions of these enzymes. This article is part of a Special Issue entitled: Respiratory Oxidases.  相似文献   

8.
《BBA》2006,1757(9-10):1122-1132
The PM  F transition of the catalytic cycle of cytochrome c oxidase from bovine heart was investigated using single-electron photoreduction and monitoring the subsequent events using spectroscopic and electometric techniques. The PM state of the oxidase was generated by exposing the oxidized enzyme to CO plus O2. Photoreduction results in rapid electron transfer from heme a to oxoferryl heme a3 with a time constant of about 0.3 ms, as indicated by transients at 605 nm and 580 nm. This rate is ∼ 5-fold more rapid than the rate of electron transfer from heme a to heme a3 in the F  O transition, but is significantly slower than formation of the F state from the PR intermediate in the reaction of the fully reduced enzyme with O2 to form state F (70–90 μs). The ∼ 0.3 ms PM  F transition is coincident with a rapid photonic phase of transmembrane voltage generation, but a significant part of the voltage associated with the PM  F transition is generated much later, with a time constant of 1.3 ms. In addition, the PM  F transition of the R. sphaeroides oxidase was also measured and also was shown to have two phases of electrogenic proton transfer, with τ values of 0.18 and 0.85 ms.  相似文献   

9.
In this paper allosteric interactions in protonmotive heme aa(3) terminal oxidases of the respiratory chain are dealt with. The different lines of evidence supporting the key role of H(+)/e(-) coupling (redox Bohr effect) at the low spin heme a in the proton pump of the bovine oxidase are summarized. Results are presented showing that the I-R54M mutation in P. denitrificans aa(3) oxidase, which decreases by more than 200mV the E(m) of heme a, inhibits proton pumping. Mutational amino acid replacement in proton channels, at the negative (N) side of membrane-inserted prokaryotic aa(3) oxidases, as well as Zn(2+) binding at this site in the bovine oxidase, uncouples proton pumping. This effect appears to result from alteration of the structural/functional device, closer to the positive, opposite (P) surface, which separates pumped protons from those consumed in the reduction of O(2) to 2 H(2)O.  相似文献   

10.
《BBA》2023,1864(2):148937
Bovine cytochrome c oxidase (CcO) contains two hemes, a and a3, chemically identical but differing in coordination and spin state. The Soret absorption band of reduced aa3-type cytochrome c oxidase consists of overlapping bands of the hemes a2+ and a32+. It shows a peak at ~444 nm and a distinct shoulder at ~425 nm. However, attribution of individual spectral lineshapes to hemes a2+ and a32+ in the Soret is controversial. In the present work, we characterized spectral contributions of hemes a2+ and a32+ using two approaches. First, we reconstructed bovine CcO heme a2+ spectrum using a selective Ca2+-induced spectral shift of the heme a2+. Second, we investigated photobleaching of the reduced Thermus thermophilus ba3- and bovine aa3-oxidases in the Soret induced by femtosecond laser pulses in the Q-band. The resolved spectra show splitting of the electronic B0x-, B0y-transitions of both reduced hemes. The heme a2+ spectrum is shifted to the red relative to heme a32+ spectrum. The ~425 nm shoulder is mostly attributed to heme a32+.  相似文献   

11.
Identification of the intermediates and determination of their structures in the reduction of dioxygen to water by cytochrome c oxidase (CcO) are particularly important to understanding both O2 activation and proton pumping by the enzyme. In this work, we report the products of the rapid reaction of O2 with the mixed valence form (CuA2+, heme a3+, heme a32+-CuB1+) of the enzyme. The resonance Raman results show the formation of two ferryl-oxo species with characteristic Fe(IV)=O stretching modes at 790 and 804 cm−1 at the peroxy oxidation level (PM). Density functional theory calculations show that the protein environment of the proximal H-bonded His-411 determines the strength of the distal Fe(IV)=O bond. In contrast to previous proposals, the PM intermediate is also formed in the reaction of Y167F with O2. These results suggest that in the fully reduced enzyme, the proton pumping νFe(IV)=O = 804 cm−1 to νFe(IV)=O = 790 cm−1 transition (P→F, where P is peroxy and F is ferryl) is triggered not only by electron transfer from heme a to heme a3 but also by the formation of the H-bonded form of the His-411-Fe(IV)=O conformer in the proximal site of heme a3. The implications of these results with respect to the role of an O=Fe(IV)-His-411-H-bonded form to the ring A propionate of heme a3-Asp-399-H2O site and, thus, to the exit/output proton channel (H2O) pool during the proton pumping P→F transition are discussed. We propose that the environment proximal to the heme a3 controls the spectroscopic properties of the ferryl intermediates in cytochrome oxidases.  相似文献   

12.
While applications of amine oxidases are increasing, few have been characterised and our understanding of their biological role and strategies for bacteria exploitation are limited. By altering the nitrogen source (NH4Cl, putrescine and cadaverine (diamines) and butylamine (monoamine)) and concentration, we have identified a constitutive flavin dependent oxidase (EC 1.4.3.10) within Rhodococcus opacus. The activity of this oxidase can be increased by over two orders of magnitude in the presence of aliphatic diamines. In addition, the expression of a copper dependent diamine oxidase (EC 1.4.3.22) was observed at diamine concentrations > 1 mM or when cells were grown with butylamine, which acts to inhibit the flavin oxidase. A Michaelis–Menten kinetic treatment of the flavin oxidase delivered a Michaelis constant (KM) = 190 μM and maximum rate (kcat) = 21.8 s?1 for the oxidative deamination of putrescine with a lower KM (=60 μM) and comparable kcat (=18.2 s?1) for the copper oxidase. MALDI–TOF and genomic analyses have indicated a metabolic clustering of functionally related genes. From a consideration of amine oxidase specificity and sequence homology, we propose a putrescine degradation pathway within Rhodococcus that utilises oxidases in tandem with subsequent dehydrogenase and transaminase enzymes. The implications of PUT homeostasis through the action of the two oxidases are discussed with respect to stressors, evolution and application in microbe-assisted phytoremediation or bio-augmentation.  相似文献   

13.
Salts inhibit the activity of sweet almond β-glucosidase. For cations (Cl salts) the effectiveness follows the series: Cu+2, Fe+2 > Zn+2 > Li+ > Ca+2 > Mg+2 > Cs+ > NH4+ > Rb+ > K+ > Na+ and for anions (Na+ salts) the series is: I > ClO4 > SCN > Br  NO3 > Cl  OAc > F  SO4 2. The activity of the enzyme, like that of most glycohydrolases, depends on a deprotonated carboxylate (nucleophile) and a protonated carboxylic acid for optimal activity. The resulting pH-profile of kcat/Km for the β-glucosidase-catalyzed hydrolysis of p-nitrophenyl glucoside is characterized by a width at half height that is strongly sensitive to the nature and concentration of the salt. Most of the inhibition is due to a shift in the enzymic pKas and not to an effect on the pH-independent second-order rate constant, (kcat/Km)lim. For example, as the NaCl concentration is increased from 0.01 M to 1.0 M the apparent pKa1 increases (from 3.7 to 4.9) and the apparent pKa2 decreases (from 7.2 to 5.9). With p-nitrophenyl glucoside, the value of the pH-independent (kcat/Km)lim (= 9 × 104 M 1 s 1) is reduced by less than 4% as the NaCl concentration is increased. There is a similar shift in the pKas when the LiCl concentration is increased to 1.0 M. The results of these salt-induced pKa shifts rule out a significant contribution of reverse protonation to the catalytic efficiency of the enzyme. At low salt concentration, the fraction of the catalytically active monoprotonated enzyme in the reverse protonated form (i.e., proton on the group with a pKa of 3.7 and dissociated from the group with a pKa of 7.2) is very small (≈ 0.03%). At higher salt concentrations, where the two pKas become closer, the fraction of the monoprotonated enzyme in the reverse protonated form increases over 300-fold. However, there is no increase in the intrinsic reactivity, (kcat/Km)lim, of the monoprotonated species. For other enzymes which may show such salt-induced pKa shifts, this provides a convenient test for the role of reverse protonation.  相似文献   

14.
PurposeTo measure the environmental doses from stray neutrons in the vicinity of a solid slab phantom as a function of beam energy, field size and modulation width, using the proton pencil beam scanning (PBS) technique.MethodMeasurements were carried out using two extended range WENDI-II rem-counters and three tissue equivalent proportional counters. Detectors were suitably placed at different distances around the RW3 slab phantom. Beam irradiation parameters were varied to cover the clinical ranges of proton beam energies (100–220 MeV), field sizes ((2 × 2)–(20 × 20) cm2) and modulation widths (0–15 cm).ResultsFor pristine proton peak irradiations, large variations of neutron H1(10)/D were observed with changes in beam energy and field size, while these were less dependent on modulation widths. H1(10)/D for pristine proton pencil beams varied between 0.04 μSv Gy−1 at beam energy 100 MeV and a (2 × 2) cm2 field at 2.25 m distance and 90° angle with respect to the beam axis, and 72.3 μSv Gy−1 at beam energy 200 MeV and a (20 × 20) cm2 field at 1 m distance along the beam axis.ConclusionsThe obtained results will be useful in benchmarking Monte Carlo calculations of proton radiotherapy in PBS mode and in estimating the exposure to stray radiation of the patient. Such estimates may be facilitated by the obtained best-fitted simple analytical formulae relating the stray neutron doses at points of interest with beam irradiation parameters.  相似文献   

15.
The kinetics of single-electron injection into the oxidized nonrelaxed state (OH → EH transition) of the aberrant ba3 cytochrome oxidase from Thermus thermophilus, noted for its lowered efficiency of proton pumping, was investigated by time-resolved optical spectroscopy. Two main phases of intraprotein electron transfer were resolved. The first component (τ ∼ 17 μs) reflects oxidation of CuA and reduction of the heme groups (low-spin heme b and high-spin heme a3 in a ratio close to 50:50). The subsequent component (τ ∼ 420 μs) includes reoxidation of both hemes by CuB. This is in significant contrast to the OH → EH transition of the aa3-type cytochrome oxidase from Paracoccus denitrificans, where the fastest phase is exclusively due to transient reduction of the low-spin heme a, without electron equilibration with the binuclear center. On the other hand, the one-electron reduction of the relaxed O state in ba3 oxidase was similar to that in aa3 oxidase and only included rapid electron transfer from CuA to the low-spin heme b. This indicates a functional difference between the relaxed O and the pulsed OH forms also in the ba3 oxidase from T. thermophilus.  相似文献   

16.
Proton (H+ ion) budgets were calculated for 17 forested sites in Europe using open field (bulk) and throughfall deposition and runoff or soil leachate data. Proton budgets integrate information about the complex chemical and biological processes that govern the generation or consumption of acidity in the ecosystem into a single parameter. The sites belong to the multidisciplinary ICP integrated monitoring network, set up to assess the environmental impacts of transboundary air pollution. Mean annual H+ budgets were estimated to quantify the relative importance of different biogeochemical processes, with special emphasis on the N deposition. N deposition exceeded S deposition on an equivalent basis at the studied sites. Model based estimates for quantifying the impact of agreed international emission reduction measures showed that the relative importance of N deposition still is likely to increase in the future. Base cation weathering and ion exchange were the main processes for proton consumption. Sites on base poor soil material showed low base cation fluxes, export of acidity and high external/internal H+ source ratios. At these sites the dissociation of organic acids was commonly a significant internal H+ source. Depending on deposition inputs, the importance of N processes on the H+ budget varied between −4.5 mequiv. m−2 a−1 (small H+ consumption) and 46.2 mequiv. m−2 a−1 (H+ production). A relationship between the deposition inputs and the H+ production from N transformations was also observed, with higher H+ production at higher deposition levels. Net release of sulphate (and associated H+ production) was observed at many sites, being consistent with observations from other recent European budget studies.  相似文献   

17.
The α-aminoketone 1,4-diamino-2-butanone (DAB), a putrescine analogue, is highly toxic to various microorganisms, including Trypanosoma cruzi. However, little is known about the molecular mechanisms underlying DAB's cytotoxic properties. We report here that DAB (pKa 7.5 and 9.5) undergoes aerobic oxidation in phosphate buffer, pH 7.4, at 37 °C, catalyzed by Fe(II) and Cu(II) ions yielding NH4+ ion, H2O2, and 4-amino-2-oxobutanal (oxoDAB). OxoDAB, like methylglyoxal and other α-oxoaldehydes, is expected to cause protein aggregation and nucleobase lesions. Propagation of DAB oxidation by superoxide radical was confirmed by the inhibitory effect of added SOD (50 U ml? 1) and stimulatory effect of xanthine/xanthine oxidase, a source of superoxide radical. EPR spin trapping studies with 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) revealed an adduct attributable to DMPO–HO?, and those with α-(4-pyridyl-1-oxide)-N-tert-butylnitrone or 3,5-dibromo-4-nitrosobenzenesulfonic acid, a six-line adduct assignable to a DAB? resonant enoyl radical adduct. Added horse spleen ferritin (HoSF) and bovine apo-transferrin underwent oxidative changes in tryptophan residues in the presence of 1.0–10 mM DAB. Iron release from HoSF was observed as well. Assays performed with fluorescein-encapsulated liposomes of cardiolipin and phosphatidylcholine (20:80) incubated with DAB resulted in extensive lipid peroxidation and consequent vesicle permeabilization. DAB (0–10 mM) administration to cultured LLC-MK2 epithelial cells caused a decline in cell viability, which was inhibited by preaddition of either catalase (4.5 μM) or aminoguanidine (25 mM). Our findings support the hypothesis that DAB toxicity to several pathogenic microorganisms previously described may involve not only reported inhibition of polyamine metabolism but also DAB pro-oxidant activity.  相似文献   

18.
《Process Biochemistry》2014,49(12):2149-2157
The cell-bound cholesterol oxidase from the Rhodococcus sp. NCIM 2891 was purified three fold by diethylaminoethyl–sepharose chromatography. The estimated molecular mass (SDS-PAGE) and Km of the enzyme were ∼55.0 kDa and 151 μM, respectively. The purified cholesterol oxidase was immobilized on chitosan beads by glutaraldehyde cross-linking reaction and immobilization was confirmed by Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray analysis. The optimum temperature (45 °C, 5 min) for activity of the enzyme was increased by 5 °C after immobilization. Both the free and immobilized cholesterol oxidases were found to be stable in many organic solvents except for acetone. Fe2+ and Pb2+ at 0.1 mM of each acted as inhibitors, while Ag+, Ca2+, Ni2+ and Zn2+ activated the enzyme at similar concentration. The biotransformation of cholesterol (3.75 mM) with the cholesterol oxidase immobilized beads (3.50 U) leads to ∼88% millimolar yield of cholestenone in a reaction time of 9 h at 25 °C. The immobilized enzyme retains ∼67% activity even after 12 successive batches of operation. The biotransformation method thus, shows a great promise for the production of pharmaceutically important cholestenone.  相似文献   

19.
The complete understanding of a molecular mechanism of action requires the thermodynamic and kinetic characterization of different states and intermediates. Cytochrome c oxidase reduces O2 to H2O, a reaction coupled to proton translocation across the membrane. Therefore, it is necessary to undertake a thorough characterization of the reduced form of the enzyme and the determination of the electron transfer processes and pathways between the redox-active centers. In this study Fourier transform infrared (FTIR) and time-resolved step-scan FTIR spectroscopy have been applied to study the fully reduced and mixed valence states of cytochrome ba3 from Thermus thermophilus. We used as probe carbon monoxide (CO) to characterize both thermodynamically and kinetically the cytochrome ba3-CO complex in the 5.25–10.10 pH/pD range and to study the reverse intramolecular electron transfer initiated by the photolysis of CO in the two-electron reduced form. The time-resolved step-scan FTIR data revealed no pH/pD dependence in both the decay of the transient CuB1+-CO complex and rebinding to heme a3 rates, suggesting that no structural change takes place in the vicinity of the binuclear center. Surprisingly, photodissociation of CO from the mixed valence form of the enzyme does not lead to reverse electron transfer from the reduced heme a3 to the oxidized low-spin heme b, as observed in all the other aa3 and bo3 oxidases previously examined. The heme b-heme a3 electron transfer is guaranteed, and therefore, there is no need for structural rearrangements and complex synchronized cooperativities. Comparison among the available structures of ba3- and aa3-cytochrome c oxidases identifies possible active pathways involved in the electron transfer processes and key structural elements that contribute to the different behavior observed in cytochrome ba3.  相似文献   

20.
The biogeochemical cycles of nitrogen (N) and base cations (BCs), (i.e., K+, Na+, Ca2+, and Mg2+), play critical roles in plant nutrition and ecosystem function. Empirical correlations between large experimental N fertilizer additions to forest ecosystems and increased BCs loss in stream water are well demonstrated, but the mechanisms driving this coupling remain poorly understood. We hypothesized that protons generated through N transformation (PPRN)—quantified as the balance of NH4+ (H+ source) and NO3 (H+ sink) in precipitation versus the stream output will impact BCs loss in acid-sensitive ecosystems. To test this hypothesis, we monitored precipitation input and stream export of inorganic N and BCs for three years in an acid-sensitive forested watershed in a granite area of subtropical China. We found the precipitation input of inorganic N (17.71 kg N ha−1 year−1 with 54% as NH4+–N) was considerably higher than stream exported inorganic N (5.99 kg N ha−1 year−1 with 83% as NO3–N), making the watershed a net N sink. The stream export of BCs (151, 1518, 851, and 252 mol ha−1 year−1 for K+, Na+, Ca2+, and Mg2+, respectively) was positively correlated (r = 0.80, 0.90, 0.84, and 0.84 for K+, Na+, Ca2+, and Mg2+ on a monthly scale, respectively, P < 0.001, n = 36) with PPRN (389 mol ha−1 year−1) over the three years, suggesting that PPRN drives loss of BCs in the acid-sensitive ecosystem. A global meta-analysis of 15 watershed studies from non-calcareous ecosystems further supports this hypothesis by showing a similarly strong correlation between ∑BCs output and PPRN (r = 0.89, P < 0.001, n = 15), in spite of the pronounced differences in environmental settings. Collectively, our results suggest that N transformations rather than anions (NO3 and/or SO42−) leaching specifically, are an important mediator of BCs loss in acid-senstive ecosystems. Our study provides the first definitive evidence that the chronic N deposition and subsequent transformation within the watershed drive stream export of BCs through proton production in acid-sensitive ecosystems, irrespective of their current relatively high N retention. Our findings suggest the N-transformation-based proton production can be used as an indicator of watershed outflow quality in the acid-sensitive ecosystems.  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