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1.
M. Bornancin G. De Renzis J. Maetz 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1977,117(3):313-322
Summary Freshwater eel gills are notorious for their limited ability to pump chloride. As a result there is a considerable discrepancy between the Na+ and Cl– plasma levels, and plasma HCO3
– and blood pH are relatively high in this species.When eels are kept in tanks aerated with pure oxygen, significant alterations in blood acid-base balance, an increase in plasma pCO2 and a decrease in blood pH, are observed. In fish studied after 3 weeks hyperoxia, the decrease in blood pH is compensated by an increase in plasma HCO3
–. Such fish exhibit a Cl– influx 5 times higher than that observed in normoxic fish. This Cl– influx is readily inhibited by addition of SCN– to the external medium.An anion-stimulated ATPase activated by HCO3
– and by Cl– and inhibited by SCN– was recently described in membrane fractions of the gills ofCarassius auratus, a fish noted for its high Cl– pumping rate. This enzyme is also found in the gills of the eel. While the maximal rates of enzyme activation by HCO3
– and by Cl– are similar inCarassius andAnguilla, the affinity of the enzyme for Cl– is 25 times higher inCarassius. In the microsomal fraction of the hyperoxic eel gills, the maximal anionstimulated ATPase activity remains unchanged but HCO3
– affinity decreases by 50%, while Cl– affinity increases 5 times. Thus some characteristics of this ATPase seem to be closely related to the Cl– pump activity exhibited by the gill in fresh water. 相似文献
2.
Inorganic Carbon Uptake during Photosynthesis : II. Uptake by Isolated Asparagus Mesophyll Cells during Isotopic Disequilibrium 总被引:3,自引:3,他引:0
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The species of inorganic carbon (CO2 or HCO3−) taken up a source of substrate for photosynthetic fixation by isolated Asparagus sprengeri mesophyll cells is investigated. Discrimination between CO2 or HCO3− transport, during steady state photosynthesis, is achieved by monitoring the changes (by 14C fixation) which occur in the specific activity of the intracellular pool of inorganic carbon when the inorganic carbon present in the suspending medium is in a state of isotopic disequilibrium. Quantitative comparisons between theoretical (CO2 or HCO3− transport) and experimental time-courses of 14C incorporation, over the pH range of 5.2 to 7.5, indicate that the specific activity of extracellular CO2, rather than HCO3−, is the appropriate predictor of the intracellular specific activity. It is concluded, therefore, that CO2 is the major source of exogenous inorganic carbon taken up by Asparagus cells. However, at high pH (8.5), a component of net DIC uptake may be attributable to HCO3− transport, as the incorporation of 14C during isotopic disequilibrium exceeds the maximum possible incorporation predicted on the basis of CO2 uptake alone. The contribution of HCO3− to net inorganic carbon uptake (pH 8.5) is variable, ranging from 5 to 16%, but is independent of the extracellular HCO3− concentration. The evidence for direct HCO3− transport is subject to alternative explanations and must, therefore, be regarded as equivocal. Nonlinear regression analysis of the rate of 14C incorporation as a function of time indicates the presence of a small extracellular resistance to the diffusion of CO2, which is partially alleviated by a high extracellular concentration of HCO3−. 相似文献
3.
F. Trischitta M. G. Denaro C. Faggio F. Fucile T. Schettino 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1994,164(4):286-291
The sensitivity to external pH of Cl- absorption was studied in isolated stripped intestinal mucosa of the eel, Anguilla anguilla, mounted in Ussing chambers. Short-circuit current, transepithelial potential difference and conductance were measured in bathing solutions containing various combinations of HCO3
--concentration (0–25 mmol·l-1), partial pressure of CO2 (0–76 mm Hg) and pH (6.9–7.9). A linear relationship was found between pH and short-circuit current in the range of pH studied both in HCO3
-/CO2 Ringer and in Hepes Ringer. The pH effect was almost completely reversible. It was not affected by the presence of mucosal Ba2+ (10-3 mol·l-1) but it was inhibited by the presence of luminal (10-5 mol·l-1) or serosal (10-4 mol·l-1) bumetanide. The results obtained suggest that the Cl- absorption in the European eel intestine is pH sensitive. The data do not indicate whether the pH affects directly the Na+–K+–Cl- cotransport and/or the basolateral Cl- conductance or other mechanisms indirectly linked to Cl- absorption.Abbreviations g
t
transepithelial conductance
- Hepes
N-2-Hydroxyethylpiperazine-N'-2-ethanesulfonic acid
-
I
sc
short circuit current
-
R
t
transepithelial resistence
-
V
t
transepithelial potential difference 相似文献
4.
Two Systems for Concentrating CO(2) and Bicarbonate during Photosynthesis by Scenedesmus 总被引:5,自引:3,他引:2
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Scenedesmus cells grown on high CO2, when adapted to air levels of CO2 for 4 to 6 hours in the light, formed two concentrating processes for dissolved inorganic carbon: one for utilizing CO2 from medium of pH 5 to 8 and one for bicarbonate accumulation from medium of pH 7 to 11. Similar results were obtained with assays by photosynthetic O2 evolution or by accumulation of dissolved inorganic carbon inside the cells. The CO2 pump with K0.5 for O2 evolution of less than 5 micromolar CO2 was similar to that previously studied with other green algae such as Chlamydomonas and was accompanied by plasmalemma carbonic anhydrase formation. The HCO3− concentrating process between pH 8 to 10 lowered the K0.5 (DIC) from 7300 micromolar HCO3− in high CO2 grown Scenedesmus to 10 micromolar in air-adapted cells. The HCO3− pump was inhibited by vanadate (Ki of 150 micromolar), as if it involved an ATPase linked HCO3− transporter. The CO2 pump was formed on low CO2 by high-CO2 grown cells in growth medium within 4 to 6 hours in the light. The alkaline HCO3− pump was partially activated on low CO2 within 2 hours in the light or after 8 hours in the dark. Full activation of the HCO3− pump at pH 9 had requirements similar to the activation of the CO2 pump. Air-grown or air-adapted cells at pH 7.2 or 9 accumulated in one minute 1 to 2 millimolar inorganic carbon in the light or 0.44 millimolar in the dark from 150 micromolar in the media, whereas CO2-grown cells did not accumulate inorganic carbon. A general scheme for concentrating dissolved inorganic carbon by unicellular green algae utilizes a vanadate-sensitive transporter at the chloroplast envelope for the CO2 pump and in some algae an additional vanadate-sensitive plasmalemma HCO3− transporter for a HCO3− pump. 相似文献
5.
Mark O. Bevensee Michael Apkon Walter F. Boron 《The Journal of general physiology》1997,110(4):467-483
In the preceding paper (Bevensee, M.O., R.A. Weed, and W.F. Boron. 1997. J. Gen. Physiol. 110: 453–465.), we showed that a Na+-driven influx of HCO3
− causes the increase in intracellular pH (pHi) observed when astrocytes cultured from rat hippocampus are exposed to 5% CO2/17 mM HCO3
−. In the present study, we used the pH-sensitive fluorescent indicator 2′,7′-biscarboxyethyl-5,6-carboxyfluorescein (BCECF) and the perforated patch-clamp technique to determine whether this transporter is a Na+-driven Cl-HCO3 exchanger, an electrogenic Na/HCO3 cotransporter, or an electroneutral Na/HCO3 cotransporter. To determine if the transporter is a Na+-driven Cl-HCO3 exchanger, we depleted the cells of intracellular Cl− by incubating them in a Cl−-free solution for an average of ∼11 min. We verified the depletion with the Cl−-sensitive dye N-(6-methoxyquinolyl)acetoethyl ester (MQAE). In Cl−-depleted cells, the pHi still increases after one or more exposures to CO2/HCO3
−. Furthermore, the pHi decrease elicited by external Na+ removal does not require external Cl−. Therefore, the transporter cannot be a Na+-driven Cl-HCO3 exchanger. To determine if the transporter is an electrogenic Na/ HCO3 cotransporter, we measured pHi and plasma membrane voltage (Vm) while removing external Na+, in the presence/absence of CO2/HCO3
− and in the presence/absence of 400 μM 4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid (DIDS). The CO2/HCO3
− solutions contained 20% CO2 and 68 mM HCO3
−, pH 7.3, to maximize the HCO3
− flux. In pHi experiments, removing external Na+ in the presence of CO2/HCO3
− elicited an equivalent HCO3
− efflux of 281 μM s−1. The HCO3
− influx elicited by returning external Na+ was inhibited 63% by DIDS, so that the predicted DIDS-sensitive Vm change was 3.3 mV. Indeed, we found that removing external Na+ elicited a DIDS-sensitive depolarization that was 2.6 mV larger in the presence than in the absence of CO2/ HCO3
−. Thus, the Na/HCO3 cotransporter is electrogenic. Because a cotransporter with a Na+:HCO3
− stoichiometry of 1:3 or higher would predict a net HCO3
− efflux, rather than the required influx, we conclude that rat hippocampal astrocytes have an electrogenic Na/HCO3 cotransporter with a stoichiometry of 1:2. 相似文献
6.
Photorespiration and Internal CO(2) Accumulation in Chara corallina as Inferred from the Influence of DIC and O(2) on Photosynthesis
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An O2 electrode system with a specially designed chamber for `whorl' cell complexes of Chara corallina was used to study the combined effects of inorganic carbon and O2 concentrations on photosynthetic O2 evolution. At pH = 5.5 and 20% O2, cells grown in HCO3− medium (low CO2, pH ≥ 9.0) exhibited a higher affinity for external CO2 (K½(CO2) = 40 ± 6 micromolar) than the cells grown for at least 24 hours in high-CO2 medium (pH = 6.5), (K½(CO2) = 94 ± 16 micromolar). With O2 ≤ 2% in contrast, both types of cells showed a high apparent affinity (K½(CO2) = 50 − 52 micromolar). A Warburg effect was detectable only in the low affinity cells previously cultivated in high-CO2 medium (pH = 6.5). The high-pH, HCO3−-grown cells, when exposed to low pH (5.5) conditions, exhibited a response indicating an ability to fix CO2 which exceeded the CO2 externally supplied, and the reverse situation has been observed in high-CO2-grown cells. At pH 8.2, the apparent photosynthetic affinity for external HCO3− (K½[HCO3−]) was 0.6 ± 0.2 millimolar, at 20% O2. But under low O2 concentrations (≤2%), surprisingly, an inhibition of net O2 evolution was elicited, which was maximal at low HCO3− concentrations. These results indicate that: (a) photorespiration occurs in this alga and can be revealed by cultivation in high-CO2 medium, (b) Chara cells are able to accumulate CO2 internally by means of a process apparently independent of the plasmalemma HCO3− transport system, (c) molecular oxygen appears to be required for photosynthetic utilization of exogenous HCO3−: pseudocyclic electron flow, sustained by O2 photoreduction, may produce the additional ATP needed for the HCO3− transport. 相似文献
7.
Summary Cells ofChara corallina grown under high CO2 culture conditions were able to utilize exogenous HCO3
– to give appreciable rates of net photosynthesis. Since these rates of photosynthesis could be detected within 10 min of being transferred from high-CO2 to normal HCO3
– (pH 8.2) culture conditions, it would appear that the HCO3
–-accumulating system ofChara is not fully repressed under these high CO2 culture conditions. The membrane potential of these cells also responded to light/dark treatments in a manner consistent with the operation of a HCO3
– acquisition system. With prolonged exposure (2–6 days) to CPW/B, net photosynthesis continued to increase towards the expected control rate and, in parallel, the electrical responses elicited by light/dark treatments converged towards those obtained on control (CPW/B-grown)Chara cells. Charasomes were absent in CPW/CO2-grownChara, but redeveloped in mature cells once the culture was returned to CPW/B conditions; a minimum period of 7 days in CPW/B was required before charasomes were detected in tissue examined in the transmission electron microscope. As the above-detailed physiological and electrophysiological features were observed with both axial and whorl cells ofChara in which charasomes were completely absent, we conclude that this specialized organelle is not an essential component for photosynthetic utilization of exogenous HCO3
– in this species.Abbreviations CPW/B
Chara pond water containing 1.0 mM NaHCO3, pH8.2
- CPW/CO2
Chara pond water containing dissolved CO2, pH 5.5
- DIC
dissolved in organic carbon
- D.H.
dark-induced membrane hyperpolarization
- L.H.
light-induced membrane hyperpolarization
- TEM
transmission electron microscopy 相似文献
8.
Pathways for HCO3− transport across the basolateral membrane were investigated using membrane vesicles isolated from rat renal cortex. The presence of Cl−---HCO3− exchange was assessed directly by 36Cl− tracer flux measurements and indirectly by determinants of acridine orange absorbance changes. Under 10% CO2/90% N2 the imposition of an outwardly directed HCO3− concentration gradient (pHo 6/pHi 7.5) stimulated Cl− uptake compared to Cl− uptake under 100% N2 in the presence of a pH gradient alone. Mediated exchange of Cl− for HCO3 was suggested by the HCO3− gradient-induced concentrative accumulation of intravesicular Cl−. Maneuvers designed to offset the development of ion-gradient-induced diffusion potentials had no significant effect on the magnitude of HCO3− gradient-driven Cl− uptake further suggesting chemical as opposed to electrical Cl−HCO3− exchange coupling. Although basolateral membrane vesicle Cl− uptake was observed to be voltage sensitive, the DIDS insensitivity of the Cl conductive pathway served to distinguish this mode of Cl− translocation from HCO3 gradient-driven Cl− uptake. No evidence for
cotransport was obtained. As determined by acridine orange absorbance measurements in the presence of an imposed pH gradient (pHo 7.5/pHi 6), a HCO3− dependent increase in the rate of intravesicular alkalinization was observed in response to an outwardly directed Cl− concentration gradient. The basolateral membrane vesicle origin of the observed Cl−−HCO3− exchange activity was verified by experiments performed with purified brush-border membrane vesicles. In contrast to our previous observations of the effect of Cl− on HCO3− gradient-driven Na+ uptake suggesting a basolateral membrane Na+−HCO3− for Cl− exchange mechanism, no effect of Na+ on Cl−HCO3− exchange was observed in the present study. 相似文献
9.
Summary Active HCO
3
t-
secretion in the anterior rectal salt gland of the mosquito larva,Aedes dorsalis, is mediated by a 11 Cl–/HCO
3
–
exchanger. The cellular mechanisms of HCO
3
–
and Cl– transport are examined using ion- and voltage-sensitive microelectrodes in conjunction with a microperfused preparation which allowed rapid saline changes. Addition of DIDS or acetazolamide to, or removal of CO2 and HCO
3
–
from, the serosal bath caused large (20 to 50 mV) hyperpolarizations of apical membrane potential (V
a) and had little effect on basolateral potential (V
bl). Changes in luminal Cl– concentration alteredV
a in a repid, linear manner with a slope of 42.2 mV/decaloga
Cl
l
–. Intracellular Cl– activity was 23.5mm and was approximately 10mm lower than that predicted for a passive distribution across the apical membrane. Changes in serosal Cl– concentration had no effect onV
bl, indicating an electrically silent basolateral Cl– exit step. Intracellular pH in anterior rectal cells was 7.67 and the calculated
was 14.4mm. These results show that under control conditions HCO3 enters the anterior rectal cell by an active mechanism against an electrochemical gradient of 77.1 mV and exits the cell at the apical membrane down a favorable electrochemical gradient of 27.6 mV. A tentative cellular model is proposed in which Cl enters the apical membrane of the anterior rectal cells by passive, electrodiffusive movement through a Cl–-selective channel, and HCO
3
–
exits the cell by an active or passive electrogenic transport mechanism. The electrically silent nature of basolateral Cl– exit and HCO3 entry, and the effects of serosal addition of the Cl–/HCO3 exchange inhibitor, DIDS, on
and transepithelial potential (V
ic) suggest strongly that the basolateral membrane is the site of a direct coupling between Cl– and HCO
3
–
movements. 相似文献
10.
Light-Induced Proton Release by the Cyanobacterium Anabaena variabilis: Dependence on CO(2) and Na 总被引:3,自引:1,他引:2
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Light-induced acidification by the cyanobacterium Anabaena variabilis is biphasic (a fast phase I and slow phase II) and shown to be sodium-dependent with an optimum concentration of 40 to 60 millimolar Na+. Cells grown under low CO2 concentrations at pH 9 (i.e. mainly HCO3− present in the medium) exhibited the slow phase II of proton efflux only, while cells grown under low CO2 concentrations at pH 6.3 (i.e. CO2 and HCO3− present) exhibited both phases. Light-induced proton release of phase I was dependent on inorganic carbon available in the bathing medium with an apparent Km for CO2 of 20 to 70 micromolar. As was concluded from the CO2 dependence of acidification measured at different pH of the bathing medium, bicarbonate inhibited phase-I acidification noncompetetively. Acidification was inhibited by acetazolamide, an inhibitor of carbonic anhydrase. Apparently, acidification of phase I is due to a light-dependent uptake of CO2 being converted to HCO3− by a carbonic anhydrase-like function of the HCO3−-transport system (M Volokita, D Zenvirth, A Kaplan, L Reinhold 1984 Plant Physiol 76: 599-602) before or during entering the cell, thus releasing one proton per CO2 converted to HCO3−. 相似文献
11.
Inorganic Carbon Uptake by Chlamydomonas reinhardtii 总被引:15,自引:12,他引:3
The rates of CO2-dependent O2 evolution by Chlamydomonas reinhardtii, grown with either air levels of CO2 or air with 5% CO2, were measured at varying external pH. Over a pH range of 4.5 to 8.5, the external concentration of CO2 required for half-maximal rates of photosynthesis was constant, averaging 25 micromolar for cells grown with 5% CO2. This is consistent with the hypothesis that these cells take up CO2 but not HCO3− from the medium and that their CO2 requirement for photosynthesis reflects the Km(CO2) of ribulose bisphosphate carboxylase. Over a pH range of 4.5 to 9.5, cells grown with air required an external CO2 concentration of only 0.4 to 3 micromolar for half-maximal rates of photosynthesis, consistent with a mechanism to accumulate external inorganic carbon in these cells. Air-grown cells can utilize external inorganic carbon efficiently even at pH 4.5 where the HCO3− concentration is very low (40 nanomolar). However, at high external pH, where HCO3− predominates, these cells cannot accumulate inorganic carbon as efficiently and require higher concentrations of NaHCO3 to maintain their photosynthetic activity. These results imply that, at the plasma membrane, CO2 is the permeant inorganic carbon species in air-grown cells as well as in cells grown on 5% CO2. If active HCO3− accumulation is a step in CO2 concentration by air-grown Chlamydomonas, it probably takes place in internal compartments of the cell and not at the plasmalemma. 相似文献
12.
Carbon Oxysulfide Inhibition of the CO(2)-Concentrating Process of Unicellular Green Algae 总被引:1,自引:0,他引:1
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Carbonyl sulfide (COS), a substrate for carbonic anhydrase, inhibited alkalization of the medium, O2 evolution, dissolved inorganic carbon accumulation, and photosynthetic CO2 fixation at pH 7 or higher by five species of unicellular green algae that had been air-adapted for forming a CO2-concentrating process. This COS inhibition can be attributed to inhibition of external HCO3− conversion to CO2 and OH− by the carbonic anhydrase component of an active CO2 pump. At a low pH of 5 to 6, COS stimulated O2 evolution during photosynthesis by algae with low CO2 in the media without alkalization of the media. This is attributed to some COS hydrolysis by carbonic anhydrase to CO2. Although COS had less effect on HCO3− accumulation at pH 9 by a HCO3− pump in Scenedesmus, COS reduced O2 evolution probably by inhibiting internal carbonic anhydrases. Because COS is hydrolyzed to CO2 and H2S, its inhibition of the CO2 pump activity and photosynthesis is not accurate, when measured by O2 evolution, by NaH14CO3 accumulation, or by 14CO2 fixation. 相似文献
13.
Kenneth R. Mayes 《生物化学与生物物理学报:生物膜》1980,600(3):831-837
- 1. 1. The present experiments measure net fluxes of fluid, Cl− and HCO3− across de-epithelialised rabbit corneas clamped between half chambers and bathed in Ringer solutions.
- 2. 2. Net fluxes of HCO3− and fluid occurred together across the cornea from stroma to aqueous when HCO3− and CO2 were present in the bathing solution.
- 3. 3. No net trans-corneal Cl− flux was found
- 4. 4. The initiation of fluid flow in the presence of HCO3− and CO2 cannot be accounted for by bulk-phase osmotic flow across the cornea.
Keywords: Osmotic coupling; Bicarbonate flux; Fluid flux; Cl− flux; (Cornea) 相似文献
14.
J. A. RAVEN 《Plant, cell & environment》1997,20(2):147-154
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
15.
Uptake of HCO3? and CO2 in Cells and Chloroplasts from the Microalgae Chlamydomonas reinhardtii and Dunaliella tertiolecta
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Gabi Amoroso Dieter Sültemeyer Christoph Thyssen Heinrich P. Fock 《Plant physiology》1998,116(1):193-201
Mass-spectrometric disequilibrium analysis was applied to investigate CO2 uptake and HCO3− transport in cells and chloroplasts of the microalgae Dunaliella tertiolecta and Chlamydomonas reinhardtii, which were grown in air enriched with 5% (v/v) CO2 (high-Ci cells) or in ambient air (low-Ci cells). High- and low-Ci cells of both species had the capacity to transport CO2 and HCO3−, with maximum rates being largely unaffected by the growth conditions. In high- and low-Ci cells of D. tertiolecta, HCO3− was the dominant inorganic C species taken up, whereas HCO3− and CO2 were used at similar rates by C. reinhardtii. The apparent affinities of HCO3− transport and CO2 uptake increased 3- to 9-fold in both species upon acclimation to air. Photosynthetically active chloroplasts isolated from both species were able to transport CO2 and HCO3−. For chloroplasts from C. reinhardtii, the concentrations of HCO3− and CO2 required for half-maximal activity declined from 446 to 33 μm and 6.8 to 0.6 μm, respectively, after acclimation of the parent cells to air; the corresponding values for chloroplasts from D. tertiolecta decreased from 203 to 58 μm and 5.8 to 0.5 μm, respectively. These results indicate the presence of inducible high-affinity HCO3− and CO2 transporters at the chloroplast envelope membrane. 相似文献
16.
Forms of Dissolved Carbon Dioxide Required for Photosystem II Activity in Chloroplast Membranes 总被引:5,自引:4,他引:1
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Stemler A 《Plant physiology》1980,65(6):1160-1165
High concentrations of both bicarbonate and formate inhibit photosynthetic O2 evolution at pH 8.0. At this pH, only 2.4% of the total dissolved carbon dioxide exists as CO2. At pH 7.3, where 11% of the total dissolved carbon dioxide exists as CO2, HCO3− no longer inhibits. While formate still inhibits O2 evolution at pH 7.3, its effect can be partially overcome if CO2 is also present. The rate of binding of added 14C-labeled inorganic carbon is nearly 10-fold more rapid when the internal pH of thylakoid membranes is at 6.0 than when it is at 7.8. These observations suggest that CO2, not HCO3−, is initially bound to the photosystem II reaction center and that the location of the binding site is on the inside thylakoid surface. However, additional data presented here suggest that, after binding, CO2 is hydrated to HCO3− + H+ in a pH-dependent reaction. Two possible explanations of the “bicarbonate effect” are presented. 相似文献
17.
Na-Stimulation of Photosynthesis in the Cyanobacterium Synechococcus UTEX 625 Grown on High Levels of Inorganic Carbon 总被引:12,自引:9,他引:3
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Photosynthesis of washed cells of Synechococcus UTEX 625 grown on 5% CO2 was markedly stimulated (647 ± 50%) at pH 8.0 by the addition of low concentrations of NaCl (concentration required for half-maximal response, K½, = 18 micromolar). Studies with KCl and Na2SO4 showed that the stimulation was due to Na+. Photosynthesis at pH 6.1 was only slightly stimulated by Na+. The response of photosynthesis at pH 8.0 to [Na+] was strongly sigmoidal for dissolved inorganic carbon ([DIC] ≤ 500 micromolar). Cells grown with high total [DIC], but air-levels of CO2, at pH 9.6 showed the same response to low [Na+]. The absence of Na+ could be partially, but not completely overcome, by higher [DIC]. Various methods for examining CO2 or HCO3− use (K½CO2 determination; isotopic disequilibrium; and consideration of HCO3− dehydration rate) were consistent with CO2 use by the cells, but HCO3− use could not be ruled out. Isotopic disequilibrium studies showed that CO2 use was stimulated by Na+. Cells grown on 5% CO2 accumulated DIC against a concentration gradient by a process (or processes) dependent on Na+. No evidence for uptake of Na+ concomitant with DIC uptake could be found. The lack of O2 evolution during the initial and most rapid period of DIC accumulation suggested that the required energy was obtained from cyclic photophosphorylation. 相似文献
18.
Rat gastric mucosa was shown to contain a Mg2+-dependent ATPase which is stimulated by HCO3− at pH 8–9.Triton X-100 solubilizes this HCO3−-stimulated, Mg2+-dependent ATPase (ATP phosphohydrolase, EC 3.6.1.3).The gastric mucosa was resolved into five subcellular fractions by differential centrifugation. A large granule fraction (Fraction M), 28 000 g · min, was characterized by cytochrome c oxidase (marker enzyme for mitochondria). A microsomal fraction (Fraction P), 2 760 000 g · min, was characterized by 5′-nucleotidase(5′-ribonucleotide phosphohydrolase, EC 3.1.3.5) (plasma membrane).The Mg2+-dependent ATPase was demonstrated to have a bimodal mitochondrial membranous localization: 24% of its activity is associated with cytochrome c oxidase, and 75% with 5′-nucleotidase(5′-ribonucleotide phosphohydrolase, EC 3.1.3.5) at pH 8.The HCO3− addition resulted in two opposite effects: (1) a strong stimulation (84%) in Fraction M; (2) a slight inhibition (12%) in Fraction P.Fraction M was subfractionated by equilibration on a sucrose gradient. It gave rise to a homogeneous mitochondrial (d, 1.17–1.21) Mg2+-dependent ATPase, closely associated with cytochrome c oxidase. This ATPase is strongly stimulated (×2) by HCO3−. The subfractionation of Fraction P gave rise to two distinct ATPases: (1) the major one is associated with membranous (d, 1.10–1.15) material marked by 5′-nucleotidase and is slightly inhibited by HCO3−; (2) the other is associated with denser (d, 1.17–1.21) material and is stimulated by HCO3−.The bicarbonate-stimulated fraction of the Mg2+-dependent ATPase activity found in the gastric microsomal fraction is assumed to arise from mitochondrial cross-contamination. Further support comes from the optimal HCO3− concentration. In addition, SCN− is shown to specifically inhibit the ATPase of Fraction M.From these results it appears that the implication of HCO3−-stimulated ATPase in the gastric secretion of H+ is not as clear as had been suggested. However, in the view of an ATPase-supported model for H+ secretion, attention can be directed towards the Mg2+-dependent ATPase found to be associated with microsomes. 相似文献
19.
Active Transport of CO(2) by the Cyanobacterium Synechococcus UTEX 625 : Measurement by Mass Spectrometry 总被引:11,自引:11,他引:0
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Mass spectrometry has been used to confirm the presence of an active transport system for CO2 in Synechococcus UTEX 625. Cells were incubated at pH 8.0 in 100 micromolar KHCO3 in the absence of Na+ (to prevent HCO3− transport). Upon illumination the cells rapidly removed almost all the free CO2 from the medium. Addition of carbonic anhydrase revealed that the CO2 depletion resulted from a selective uptake of CO2, rather than a total uptake of all inorganic carbon species. CO2 transport stopped rapidly (<3 seconds) when the light was turned off. Iodoacetamide (3.3 millimolar) completely inhibited CO2 fixation but had little effect on CO2 transport. In iodoacetamide poisoned cells, transport of CO2 occurred against a concentration gradient of about 18,000 to 1. Transport of CO2 was completely inhibited by 10 micromolar diethylstilbestrol, a membrane-bound ATPase inhibitor. Studies with DCMU and PSI light indicated that CO2 transport was driven by ATP produced by cyclic or pseudocyclic photophosphorylation. Low concentrations of Na+ (<100 microequivalents per liter), but not of K+, stimulated CO2 transport as much as 2.4-fold. Unlike Na+-dependent HCO3− transport, the transport of CO2 was not inhibited by high concentrations (30 milliequivalents per liter) of Li+. During illumination, the CO2 concentration in the medium remained far below its equilibrium value for periods up to 15 minutes. This could only happen if CO2 transport was continuously occurring at a rapid rate, since the continuing dehydration of HCO3− to CO2 would rapidly raise the CO2 concentration to its equilibrium value if transport ceased. Measurement of the rate of dissolved inorganic carbon accumulation under these conditions indicated that at least part of the continuing CO2 transport was balanced by HCO3− efflux. 相似文献
20.
Photosynthesis and Inorganic Carbon Usage by the Marine Cyanobacterium, Synechococcus sp 总被引:38,自引:25,他引:13
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The marine cyanobacterium, Synechococcus sp. Nägeli (strain RRIMP N1) changes its affinity for external inorganic carbon used in photosynthesis, depending on the concentration of CO2 provided during growth. The high affinity for CO2 + HCO3− of air-grown cells (K½ < 80 nanomoles [pH 8.2]) would seem to be the result of the presence of an inducible mechanism which concentrates inorganic carbon (and thus CO2) within the cells. Silicone-oil centrifugation experiments indicate that the inorganic carbon concentration inside suitably induced cells may be in excess of 1,000-fold greater than that in the surrounding medium, and that this accumulation is dependent upon light energy. The quantum requirements for O2 evolution appear to be some 2-fold greater for low CO2-grown cells, compared with high CO2-grown cells. This presumably is due to the diversion of greater amounts of light energy into inorganic carbon transport in these cells.
A number of experimental approaches to the question of whether CO2 or HCO3− is primarily utilized by the inorganic carbon transport system in these cells show that in fact both species are capable of acting as substrate. CO2, however, is more readily taken up when provided at an equivalent concentration to HCO3−. This discovery suggests that the mechanistic basis for the inorganic carbon concentrating system may not be a simple HCO3− pump as has been suggested. It is clear, however, that during steady-state photosynthesis in seawater equilibrated with air, HCO3− uptake into the cell is the primary source of internal inorganic carbon.
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