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1.
The report of R. J. Gillies, M. P. Rosenberg, and D. W. Deamer (1981, J. Cell. Phys., 108, 115–122) that sea urchin fertilization acid is anaerobically produced CO2, was reinvestigated by inseminating Strongylocentrotus purpuratus eggs in HCO?3-free seawater, then bubbling the seawater with N2 to remove volatile acid. Fertilization acid production occurred in HCO?3-free seawater and with N2-bubbling, the pH rose 0.28 ± 0.08 unit, significantly less than the rise of 0.63 ± 0.14 unit during N2-bubbling of HCO?3-free seawater that had been acidified with CO2 and similar to the rise of 0.18 ± 0.07 unit when acidification was with HCl. We conclude that most, if not all, of the sea urchin fertilization acid is nonvolatile and thus is not CO2; since it is not a weak acid, it must be H+.  相似文献   

2.
In this study, we presented a new approach for quantification of bicarbonate (HCO3?) molecules bound to PSII. Our method, which is based on a combination of membrane-inlet mass spectrometry (MIMS) and 18O-labelling, excludes the possibility of “non-accounted” HCO3? by avoiding (1) the employment of formate for removal of HCO3? from PSII, and (2) the extremely low concentrations of HCO3?/CO2 during online MIMS measurements. By equilibration of PSII sample to ambient CO2 concentration of dissolved CO2/HCO3?, the method ensures that all physiological binding sites are saturated before analysis. With this approach, we determined that in spinach PSII membrane fragments 1.1 ± 0.1 HCO3? are bound per PSII reaction center, while none was bound to isolated PsbO protein. Our present results confirmed that PSII binds one HCO3? molecule as ligand to the non-heme iron of PSII, while unbound HCO3? optimizes the water-splitting reactions by acting as a mobile proton shuttle.  相似文献   

3.
The reaction kinetics of acetyl-coenzyme A carboxylase purified from developing castor oil seeds have been examined. On the basis of the substrate interaction and product inhibition results, a hybrid ping-pong mechanism is proposed. This type of mechanism demands that the active site of the enzyme be separated into two functionally distinct catalytic sites. The carboxybiotin intermediate formed at one site by the hydrolysis of ATP swings to the second site where acetyl-CoA is carboxylated to form malonyl-CoA. This hybrid rapid-equilibrium random bi bi uni uni ping-pong mechanism which includes the formation of three abortive complexes, E · HCO3? · ADP, E · HCO3? · Pi and E · Pi · Pi, is analogous to the hybrid ping-pong mechanism previously described for methylmalonyl-CoA transcarboxylase (D. B. Northrop (1969) J. Biol. Chem., 244, 5808) and pyruvate carboxylase (R. E. Barden, C-H. Fung, M. F. Utter, and M. C. Scrutton (1972) J. Biol. Chem., 247, 1323).  相似文献   

4.
The leakage of various inorganic carbon species from air-grown cells of Synechococcus UTEX 625 was investigated after a light to dark transition or during a light period using a mass spectrometer under a wide variety of experimental conditions. Total inorganic carbon efflux and CO2 efflux during the initial period of darkness were measured with or without carbonic anhydrase in the reaction medium respectively. The HCO3? efflux after a light to dark transition was estimated by difference. Carbon dioxide efflux in the light was measured by inhibiting CO2 transport with either Na2S or COS3 or quenching the 13C inorganic carbon transport by the addition of 12C inorganic carbon in excess. In cells in which CO2 fixation was inhibited, when only the HCO3? transport system was fully operative, CO2 effluxed continuously during the light period at a rate equal to about 25% of that in darkness. When only the CO2 transport system was operative, HCO3? effluxed during the light period. The difference between the light and dark efflux rates was consistent with a 0.6 unit decrease in the intracellular pH upon darkening the cells. The permeabilities of the cell for CO2 (2.94 ± 0.14 ± 10?8ms?1; mean ± SE, n=137) and HCO3? (1.4–1.7 ± 10?9 ms?1) were calculated.  相似文献   

5.
The photosynthetic capacity of submerged Ulva sp. when utilizing CO2 and HCO?3 as exogenous carbon forms has been investigated and compared with ambient carbon concentrations in sea water. Saturating concentrations of HCO? 3 and CO2 were 1200 and 100 μM, respectively at saturating light, and photosynthetic rates under such conditions averaged 700 μmolO2·gDW?1 ·h?1. The HCO?3 concentration of sea water (≈2500μM), was thus found to be saturating for photosynthesis of Ulva. At the CO2 concentration of sea water (≈ 10 μM), the contribution of this carbon form to photosynthesis could be 27% at the most. Under conditions of slow water movement, the relative importance of CO2 utilization would probably be minimized in favour of HCO?3 utilization. It is concluded that HCO?3 uptake is not limiting photosynthesis for Ulva under natural conditions.  相似文献   

6.
Petronijevic T., Rogers W. P. and Sommerville R. I. 1985. Carbonic acid as the host signal for the development of parasitic stages of nematodes. International Journal for Parasitology15: 661–667. This paper gives results on which may be based an identification of the component of the system CO2 + H2O ai H2CO3 ai H+ HCO3? which acts as the stimulus from the animal host for some nematodes. Using infective juveniles of Nematospiroides dubius and Haemonchus contortus, the effects on exsheathment of (1) low pCO2 values, (2) the presence of carbonic anhydrase in the stimulating medium, and (3) the inhibition of carbonic anhydrase within the juveniles have been examined. The results lead to the suggestion that it is the “readily available” undissociated H2CO3, or H2CO3 + HCO3? which is the critical factor in the stimulus for development. The wide range of [H+]s over which “readily available” H2CO3 is present in physiological environments suggests that this host signal may be important for infection with many species.  相似文献   

7.
Abstract: The role of transmembrane processes that are dependent on external anions in the regulation of cerebral intracellular pH (pHi), high-energy metabolites, and lactate was investigated using 31P and 1H NMR spectroscopy in an ex vivo brain slice preparation. During oxygenated superfusion, removal of external HCO3?/CO2 in the presence of Na+ led to a sustained split of the inorganic phosphate (Pi) peak so that the pHi indicated by one part of the peak was 0.38 pH units more alkaline and by the other part 0.10 pH units more acidic at 5 min than in the presence of HCO3?. The pH in the compartment with a higher pHi value returned to 7.29 ± 0.04 by 10.5 min of superfusion in a HCO3?-free medium, whereas the pHi in an acidic compartment was reduced to 7.02. In the presence of 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid or the absence of external Cl?, removal of HCO3? caused alkalinization without split of the Pi peak. Both treatments reduced the rate of pHi normalization following alkalinization. Simultaneous omission of external HCO3? and Na+ did not inhibit alkalinization of the pHi following CO2 exit. All these data show that the acid loading mechanism at neutral pHi is mediated by an Na+-independent anion transport. During severe hypoxia, pHi dropped from 7.29 ± 0.05 to 6.13 ± 0.16 and from 7.33 ± 0.03 to 6.67 ± 0.05 in the absence and presence of HCO3?, respectively, in Na+-containing medium. Lactate accumulated to 18.7 ± 2.8 and 19.6 ± 1.5 mmol/kg under the respective conditions. In the HCO3?-free medium supplemented with 1 mM amiloride, the pHi fell only to 6.94 ± 0.08 despite the lactate concentration of 18.9 ± 2.4 mmol/kg. Acidification caused by hypoxia was also small in the slice preparations superfused in the absence of both HCO3? and Cl?, as the pHi was 7.01 ± 0.12 at a lactate concentration of 24.5 ± 2.4 mmol/kg. These data indicate that apart from anaerobic glucose metabolism, separate acidifying mechanisms are functioning during hypoxia under these conditions. Recovery of phosphocreatine levels following reoxygenation was >75% relative to the prehypoxic level in the slice preparations superfused in the absence of HCO3? but <47% in those preparations superfused without HCO3? and Cl?. This indicates that either neutral pHi or absence of Cl? during hypoxia was deleterious to the energy metabolism. The present data indicate that Cl?/HCO3? exchange mechanisms have distinct roles in cerebral H+ homeostasis depending on the level of pHi and energy state.  相似文献   

8.
Conditions studied earlier by Tracey [(1948) Biochem. J.43, 185] are used for acid decarboxylation in sealed tubes of uronide samples supplemented with 6-14C-labeled uronic acid. The specific activity of the CO2 evolved is measured as the ratio of radioactivity to area of the CO2 peak obtained in a gas chromatogram. By appropriate standardization, samples containing some 60 nmol of uronic acid can be analyzed with reproducibility and apparent accuracy of about ±2% (mean deviation). The techniques developed for uronic acid analysis should apply with minor modification to any problem requiring accurate measurement of CO2 in small amounts.  相似文献   

9.
Influx and efflux of inorganic carbon in Synechococcus UTEX625   总被引:1,自引:0,他引:1  
The CO2 and HCO3? fluxes in air-grown cells of Synechococcus UTEX 625 al pH 8-0 were measured during dark to light and light to dark transitions using a mass spectrometer and sampling of the reaction medium. The kinetic parameters for initial uptake of CO2 and HCO3? were determined during the initial period of illumination. The development of the internal Ci pool was followed up to steady-state photosynthesis, which occurred when the size of the internal inorganic carbon pool remained apparently constant for a limited period. The experimental procedure confirmed that only CO2 transport occurred with 100mmolm?3 Na+ and that both CO2 and HCO?3 transport occurred with 25molm?3 Na+. The K1/2 values of initial CO2 and HCO3 uptake were 0.7 and 17.2 mmolm?3respectively and agreed closely with the K1/2 values of net CO2 and HCO3? transport during steady-state photosynthesis, which were 0.66 and 17.1 mmolm?3 respectively. Maximum rates of CO2and HCO3? transport were 423 and 219mmolh?1 g?1 Chl. Maximum CO2 efflux observed upon darkening was 118mmolh?1 g?1 Chl. A permeability coefficient of the cell for CO2 of 3 × 10?8 m s?1 was determined from the dark CO2 efflux assuming an internal pH of 7.2 in the dark. Following the initial CO2 uptake in the light, the extracellular [CO2] steadily declined when only CO2 transport was allowed, but an increase in the extracellular [CO2] when HCO3? transport was allowed to proceed suggested that an enhanced CO2 efflux occurred as a result of the larger size of the intracellular Ci pool.  相似文献   

10.
Rates of photosynthesis by the marine macroalga Ulva lactuca were measured in a factorial experiment at five concentrations of HCO3? and CO32- between 0·20 and 1·26 mol m?3, but very low concentrations of CO2. The results demonstrated that HCO3? was available for use, but an analysis of variance showed that CO32- had neither an inhibiting nor a stimulating effect on rates of photosynthesis over this concentration range. Over the experiment, pH varied from 8·46 to 10·06 and this also had no significant effect on rates of photosynthesis. The lack of a stimulatory effect of high concentrations of CO32- on the rate of photosynthesis at low concentrations of HCO3? was taken as circumstantial evidence for direct uptake of HCO3? rather than proton extrusion and external production of CO2. In the rockpools in which U. lactuca grows, pH values up to 10·35 have been recorded, and for much of the time, CO32- was the major form of inorganic carbon available. The apparent lack of an ability to use CO32- under these conditions suggests that direct use of CO32- as a source of inorganic carbon for photosynthesis is unlikely to be widespread.  相似文献   

11.
The reaction of Ru(XTPP)(DMF)2, where XTPP is the dianion of para substituted tetraphenylporphyrins and X is MeO, Me, H, Cl, Br, I, F, with O2 and CO were studied in DMF. The process was found to be first-order in metalloporphyrin, first-order in molecular oxygen and carbon monoxide, and second-order overall. Second-order rate constants for the CO reaction ranged from 0.170 to 0.665 M?1 s?1 at 25°C, those for the O2 reaction from 0.132 to 0.840 M?1 s?1 at 25°C. Similar activation parameters (ΔHCO± = 87 ± 1 kJ mol?1, ΔSCO± = 22 ± 4 JK?1 mol?1; ΔHO2± = 81 ± 1 kJ mol?1, and ΔSO2± = 11 ± 5 JK?1 mol?1) were found within each series. Reactivities of X substituted metalloporphyrins were found to follow different Hammett σ functions. The CO reactions correlated with σ? following normal behavior; the O2 reactions correlated with σ8° indicating O2 is π-bonded in the transition states. A dissociative mechanism is postulated for the process.  相似文献   

12.
The kinetics of HCO3?/Cl? exchange across red cell membrane of newborn infants was studied using a stopped-flow rapid reaction apparatus with a glass pH electrode attached. The measured apparent permeability P is (1.35±0.08 (S.E.)) · 10?4 cm/s (n=30) for newborns, compared with (3.1 ± 0.4) · 10?4 cm/s (n=15) for adults. These correspond to half-times of 0.2 s for newborns and 0.1 s for adults indicating that neonatal red cells exchange Cl? for HCO3? only half as fast as do adult cells. The temperature dependence of the exchange rate was studied from 2 to 42°C. From the Arrhenius plot the activation energy of the exchange process in neonatal red cells changes from 22.9 kcal/mol (low temperature) to 4.8 kcal/mol (physiological temperature) at a transition temperature of 17°C. These values are lower than the corresponding values for adult red cells, 34.7 and 10.2 kcal/mol. HCO3?/Cl? exchanges in both adult and neonatal red cells are inhibited by phlorizin. Inhibition constants Ki are 0.8 mM and 2.5 mM for adults and newborns, respectively. The differences in the values of the HCO3?/Cl? exchange rate constant and the activation energy of the exchange process between neonatal and adult red cells indicate that there is a modification of HCO3?/Cl? transport system in the neonatal red cell membranes.  相似文献   

13.
Forest soils and canopies are major components of ecosystem CO2 and CH4 fluxes. In contrast, less is known about coarse woody debris and living tree stems, both of which function as active surfaces for CO2 and CH4 fluxes. We measured CO2 and CH4 fluxes from soils, coarse woody debris, and tree stems over the growing season in an upland temperate forest. Soils were CO2 sources (4.58 ± 2.46 µmol m?2 s?1, mean ± 1 SD) and net sinks of CH4 (?2.17 ± 1.60 nmol m?2 s?1). Coarse woody debris was a CO2 source (4.23 ± 3.42 µmol m?2 s?1) and net CH4 sink, but with large uncertainty (?0.27 ± 1.04 nmol m?2 s?1) and with substantial differences depending on wood decay status. Stems were CO2 sources (1.93 ± 1.63 µmol m?2 s?1), but also net CH4 sources (up to 0.98 nmol m?2 s?1), with a mean of 0.11 ± 0.21 nmol m?2 s?1 and significant differences depending on tree species. Stems of N. sylvatica, F. grandifolia, and L. tulipifera consistently emitted CH4, whereas stems of A. rubrum, B. lenta, and Q. spp. were intermittent sources. Coarse woody debris and stems accounted for 35% of total measured CO2 fluxes, whereas CH4 emissions from living stems offset net soil and CWD CH4 uptake by 3.5%. Our results demonstrate the importance of CH4 emissions from living stems in upland forests and the need to consider multiple forest components to understand and interpret ecosystem CO2 and CH4 dynamics.  相似文献   

14.
Protoplasts were prepared from Ulva fasciata Delile, and their photosynthetic performance was measured and compared with that of thalli discs. These protoplasts maintained maximal rates of photosynthesis as high as those of thalli (up to 300 μmol O2·mg chlorophyll?1·h?1) for several hours after preparation and were therefore considered suitable for kinetic studies of inorganic carbon utilization. The photosynthetic K1/2(inorganic carbon) at pH 6.1 was 3.8 μM and increased to 67, 158, and 1410 μM at the pH values 7.0, 7.9, and 8.9, respectively. Compared with these protoplasts, thalli had a much lower affinity for CO2 but approximately the same affinity for HCO3?. Comparisons between rates of photosynthesis and the spontaneous dehydration of HCO3? (at 50 μM inorganic carbon) revealed that photosynthesis of both protoplasts (which lacked apparent activity of extracellular/surface-bound carbonic anhydrase) and thalli (which were only 25% inhibited by the external carbonic anhydrase inhibitor acetazolamide) could not be supported by CO2 formation in the medium at the higher pH values, indicating HCO3? uptake. Since both protoplasts and thalli were sensitive to 4,4′-diisothiocyanostilbene-2,2′-disulfonate, we suggest that HCO3? transport was facilitated by the membrane-located anion exchange protein recently reported to function in certain Ulva thalli. These findings suggest that the presence of a cell wall may constitute a diffusion barrier for CO2, but not for HCO3?, utilization under natural seawater conditions.  相似文献   

15.
Effects of ocean acidification on Emiliania huxleyi strain RCC 1216 (calcifying, diploid life-cycle stage) and RCC 1217 (non-calcifying, haploid life-cycle stage) were investigated by measuring growth, elemental composition, and production rates under different pCO2 levels (380 and 950 μatm). In these differently acclimated cells, the photosynthetic carbon source was assessed by a 14C disequilibrium assay, conducted over a range of ecologically relevant pH values (7.9–8.7). In agreement with previous studies, we observed decreased calcification and stimulated biomass production in diploid cells under high pCO2, but no CO2-dependent changes in biomass production for haploid cells. In both life-cycle stages, the relative contributions of CO2 and HCO3 ? uptake depended strongly on the assay pH. At pH values ≤ 8.1, cells preferentially used CO2 (≥ 90 % CO2), whereas at pH values ≥ 8.3, cells progressively increased the fraction of HCO3 ? uptake (~45 % CO2 at pH 8.7 in diploid cells; ~55 % CO2 at pH 8.5 in haploid cells). In contrast to the short-term effect of the assay pH, the pCO2 acclimation history had no significant effect on the carbon uptake behavior. A numerical sensitivity study confirmed that the pH-modification in the 14C disequilibrium method yields reliable results, provided that model parameters (e.g., pH, temperature) are kept within typical measurement uncertainties. Our results demonstrate a high plasticity of E. huxleyi to rapidly adjust carbon acquisition to the external carbon supply and/or pH, and provide an explanation for the paradoxical observation of high CO2 sensitivity despite the apparently high HCO3 ? usage seen in previous studies.  相似文献   

16.
A testable mechanism of CO2 accumulation in photolithotrophs, originally suggested by Pronina & Semenenko, is quantitatively analysed. The mechanism involves (as does the most widely accepted hypothesis) the delivery of HCO3? to the compartment containing Rubisco. It differs in proposing subsequent HCO3? entry (by passive uniport) to the thylakoid lumen, followed by carbonic anhydrase activity in the lumen; uncatalysed conversion of HCO3? to CO2, even at the low pH of the lumen, is at least 300 times too slow to account for the rate of inorganic C acquisition. Carbonic anhydrase converts the HCO3? to CO2 at the lower pH maintained in the illuminated thylakoid lumen by the light-driven H+ pump, generating CO2 at 10 times or more the thylakoid HCO3? concentration. Efflux of this CO2 can suppress Rubisco oxygenase activity and stimulate carboxylase activity in the stroma. This mechanism differs from the widely accepted hypotheses in the required location of carbonic anhydrase, i.e. in the thylakoid lumen rather than the stroma or pyrenoid, and in the need for HCO3? influx to thylakoids. The capacity for anion (assayed as Cl?) entry by passive uniport reported for thylakoid membranes is adequate for the proposed mechanism; if the Cl? channel does not transport HCO3?, HCO3? entry could be by combination of the Cl? channel with a Cl? HCO3? antiporter. This mechanism is particularly appropriate for organisms which lack overt accumulation of total inorganic C in cells, but which nevertheless have the gas exchange characteristics of an organism with a CO2-concentrating mechanism.  相似文献   

17.
Red blood cell (rbc) carbon dioxide transport was examined in vitro in three teleosts (Oncorhynchus mykiss, Anguilla anguilla, Scophthalmus maximus) and an elasmobranch (Scyliorhinus canicula) using a radioisotopic assay that measures the net conversion of plasma HCO3 to CO2. The experiments were designed to compare the intrinsic rates of rbc CO2 excretion and the impact of haemoglobin oxygenation/deoxygenation among the species.Under conditions simulating in vivo levels of plasma HCO3 and natural haematocrits, the rate of whole blood CO2 excretion varied between 14.0 μmol ml−1 h−1 (S. canicula) and 17.6 μmol ml−1 h−1 (O. mykiss). The rate of CO2 excretion in separated plasma was significantly greater in the dogfish, S. canicula. The contribution of the rbc to overall whole blood CO2 excretion was low in the dogfish (46 ± 6%) compared to the teleosts (trout, 71 ± 4%; turbot, 64 ± 5%; eel, 55 ± 3%).To eliminate the naturally occurring differences in haematocrit and plasma [HCO3] as inter-specific variables, the rates of whole blood CO2 excretion were determined in blood that had been resuspended to constant [HCO3] (5 mmol−1) and haematocrit (20%) in appropriate teleost and elasmobranch Ringer solutions. Under such normalized conditions, the rate of whole blood CO2 excretion was significantly higher in the turbot (22.4 ± 1.3 μmol ml−1 h−1) in comparison to the other species (16.4–18.4 μmol ml−1 h−1) and thus revealed a greater intrinsic rate of rbc CO2 excretion in the turbot.To study the contribution of Bohr protons, the rates of whole blood CO2 excretion were assessed in blood subjected to rapid oxygenation during the initial phase of the 3 min assay period. Rapid oxygenation significantly enhanced the rate of CO2 excretion in the teleosts but not in the elasmobranch. The extent of the increase provided by the rapid oxygenation of haemoglobin was a linear function of the extent of the Haldane effect, as quantified in each species from in vitro CO2 dissociation (combining) curves. Under steady-state conditions, deoxygenated blood exhibited greater rates of CO2 excretion than oxygenated blood in the teleosts but not in the elasmobranch. As a consequence of the Haldane effect, rbc intracellular pH was increased in the teleosts by deoxygenation but was unaltered in the elasmobranch.The results, by extrapolation, suggest that the rates of CO2 excretion in vivo are influenced by the magnitude of the Haldane effect and the extent of haemoglobin oxygenation during gill transit in addition to the intrinsic rate at which the rbc converts plasma HCO3 to CO2.  相似文献   

18.
To achieve sustainable production of biofuel from microalgae, a well-optimized and sustained biomass production is prerequisite. The major factor determining the higher productivity of algae is the availability and uptake of CO2 for biomass growth. In this study, an improved CO2 sequestration method leading to improved biomass yields has been investigated. The ability of OH? ions in fixing dissolved CO2 in form of HCO 3 ? in algal growth medium was studied using a Chlorella sp. and scaled-up in a photobioreactor. It was observed that a critical concentration of 0.005?M OH? is required for HCO 3 ? formation and utilization by algae. HCO 3 ? uptake was enhanced by 70.8% (in presence of 0.01?M NaOH) with a sixfold increase in growth rate compared with only CO2 system. In mineral carbon systems such as NaHCO3 and Na2CO3, increase in HCO 3 ? uptake was enhanced by 65.4% and 63.4%, respectively. The maximum rate of CO2 fixation of 6.6?mg?L?1?h?1 was obtained with 0.01?M NaOH which was 1.5 times compared with mineral carbon sources. The biomass from scale-up experiment contained 16.3% lipid (by weight) of which 75% is unsaturated fatty acids (in total lipids). This supports the idea that fixing the dissolved CO2 in the form of bicarbonate using alkali helps in increased biomass productivity rather than CO2 itself, forms a precursor for biodiesel, and increases CO2 sequestration in a cyclic process.  相似文献   

19.
Due to the industrial development, drinking water is getting polluted by disposing several waste products of the industries. Hardness is one of the prominent impurities in drinking water which is mainly due to the presence of carbonate and bicarbonate ions (CO3 2? and HCO3 ?) in it. Here, we present the synthesis of the zinc oxide (ZnO) and polyaniline (PANI) nanocomposite for the detection and estimation of hardness of the drinking water. The chemical formula of such a nanocomposite is defined in terms of the fraction of polyaniline nanoparticles reinforced in ZnO matrix and is derived as ZnO(1???x)PANI x (0?≤?x?≤?0.9); x is the composition ratio. Silver and ZnO(1???x)PANI x layers are coated over the unclad core of the optical fiber so as to create the four layer system as that of Kretschmann configuration SPR structure. The working principle involves the change in dielectric constant of (ZnO(1???x)PANI x ) by CO3 2? or HCO3 ? ions in aqueous atmosphere. Due to the strong interaction of the sensing surface to the CO3 2? and HCO3 ? ions, a red shift in the SPR spectrum is observed in the concentration range 0–200 μg/l. The sensitivity of the sensor depends on the composition ratio of the nanocomposite and has been found to be maximum for the composition ratio lying in the range 0.45–0.60. This has been further confirmed in terms of the enhancement of the electric field density and found to be in agreement with the experimental value. The sensitivity of the sensor with optimum value of the composition ratio is 0.094 and 0.065 nm/(μg/l) for CO3 2? and HCO3 ?, respectively. The sensor is highly selective to CO3 2? and HCO3 ?. The sensor has advantages of online monitoring and remote sensing of water quality because the probe is fabricated over an optical fiber.  相似文献   

20.
The contribution of metabolic bicarbonate to cytosolic pH (pHcyto) regulation was studied on isolated perfused rat liver using phosphorus-31 NMR spectroscopy. Removal of external HCO?3 decreased proton efflux from 18.6±5.0 to 1.64±0.29 μmol/min per g liver wet weight (w.w.) and pHcyto from 7.17±0.06 to 6.87±0.06. In the nominal absence of bicarbonate, inhibition of carbonic anhydrase by acetazolamide induced a further decrease of proton efflux of 0.69±0.26 μmol/min per g liver w.w. reflecting a reduction in metabolic CO2 hydration, and hence a decrease of H+ and HCO?3 supplies. Even though 27% of the proton efflux was amiloride-sensitive under bicarbonate-free conditions, amiloride did not change pHcyto, revealing the contribution of additional regulatory processes. Indeed, pH regulation was affected by the combined use of 4-acetamido-4′-isothiocyanostilbene-2,2′-disulfonic acid (SITS) and amiloride since pHcyto decreased by 0.16±0.05 and proton efflux by 0.60±0.14 μmol/min per g liver w.w. The data suggest that amiloride-sensitive or SITS-sensitive transport activities could achieve, by themselves, pHcyto regulation. The involvement of two mechanisms, most likely Na+/H+ antiport and Na+:HCO?3 symport, was confirmed in the whole organ under intracellular and extracellular acidosis. The evidence of Na-dependent transport of HCO?3 in the absence of exogenous bicarbonate implies that the amount of metabolic bicarbonate is sufficient to effectively participate to pHcyto regulation.  相似文献   

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