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1.
Microcystis aeruginosa Kütz. 7820 was cultured at 350 and 700 μL·L ? 1 CO2 to assess the impacts of doubled atmospheric CO2 concentration on this bloom‐forming cyanobacterium. Doubling of CO2 concentration in the airflow enhanced its growth by 52%–77%, with pH values decreased and dissolved inorganic carbon (DIC) increased in the medium. Photosynthetic efficiencies and dark respiratory rates expressed per unit chl a tended to increase with the doubling of CO2. However, saturating irradiances for photosynthesis and light‐saturated photosynthetic rates normalized to cell number tended to decrease with the increase of DIC in the medium. Doubling of CO2 concentration in the airflow had less effect on DIC‐saturated photosynthetic rates and apparent photosynthetic affinities for DIC. In the exponential phase, CO2 and HCO3 ? levels in the medium were higher than those required to saturate photosynthesis. Cultures with surface aeration were DIC limited in the stationary phase. The rate of CO2 dissolution into the liquid increased proportionally when CO2 in air was raised from 350 to 700 μL·L ? 1, thus increasing the availability of DIC in the medium and enhancing the rate of photosynthesis. Doubled CO2 could enhance CO2 dissolution, lower pH values, and influence the ionization fractions of various DIC species even when the photosynthesis was not DIC limited. Consequently, HCO3 ? concentrations in cultures were significantly higher than in controls, and the photosynthetic energy cost for the operation of CO2 concentrating mechanism might decrease. 相似文献
2.
Samir S. Badour 《Journal of phycology》1981,17(4):293-299
The time in the cell cycle when CO2 provision was required for cell development and division was determined in synchronous cultures of Chlamydomonas segnis Ettl bubbled with air (0.03% CO2) or air enriched with 5% CO2 under continuous light at 25°C and pH 7. Provision of CO2 (% in air v/v) during the G1-phase was found to be essential for the completion of the cell cycle. There was no demand for CO2 supply throughout the S-phase and mitosis. Using cultures adapted to CO2 concentrations ranging from 0.03 to 5% in air, the apparent CO2 concentration (Km) required for the cells to develop during the G-1-phase and to attain one half the maximal rates of photo-synthetic O2 evolution was calculated as 0.05%. This value increased to 0.1 and 0.5% during the S-phase. For total protein and carbohydrate accumulation, which would reflect inorganic carbon (CO2+ HCO3?) assimilation, the Km (% CO2) were ca. 0.1 and 0.14 throughout the cell cycle, respectively. The CO2 concentration at which the cells exhibited the shortest generation time (6.7 h) was 0.1%. These results showed that during development, cells photosynthesizing (evolving O2) at maximal rates but accumulating protein and carbohydrate at one half the maximal rates or less would complete their vegetative life cycle in the shortest time. 相似文献
3.
The ability of the freshwater alga, Chlorella kessleri, to maintain a carbon concentrating mechanism when grown at acid pH was investigated. The alga grows over the pH range 4.0–9.0 and was found to take up bicarbonate and CO2 actively when grown at pH 6.0. However, when grown at acid pH (below 5.5), it does not have active CO2 uptake. The acidotolerant species maintained an internal pH of 6.1–7.5 over the external pH range 4.5–7.5, thus the pH difference between the cell interior and the external medium was large enough to allow for the diffusive uptake of CO2 at acid external pH. Mass spectrometric monitoring of O2 and CO2 fluxes by suspensions of C. kessleri, grown at acid pH, and maintained at pH 7.5 showed that the rates of O2 evolution did not exceed those of CO2 uptake. The final CO2 compensation concentrations of 14.0–17.7 µM reached by photosynthetic cells were above the CO2 equilibrium concentration in the external medium, indicating a lack of active CO2 uptake at acid pH. Chlorella kessleri accumulated CO2 with internal concentrations that were 9.9, 18.7 and 22.7‐fold that of the external medium for cells grown, respectively, at pH 4.5, 5.0 and 5.5. The ability of C. kessleri cells to accumulate high intracellular concentrations of inorganic carbon at acid pH would provide a sufficiently high concentration of CO2 at the active site of Rubisco thus allowing the alga to maintain growth rates similar to those at alkaline pH. 相似文献
4.
A problem in the mass production of recombinant proteins and biopesticides using insect cell culture is CO2 accumulation. This research investigated the effect of elevated CO2 concentration on insect cell growth and metabolism. Spodoptera frugiperda Sf‐9 insect cells were grown at 20% air saturation, 27°C, and a pH of 6.2. The cells were exposed to a constant CO2 concentration by purging the medium with CO2 and the headspace with air. The population doubling time (PDT) of Sf‐9 cells increased with increasing CO2 concentration. Specifically, the PDT for 0‐37, 73, 147, 183, and 220 mm Hg CO2 concentrations were 23.2 ± 6.7, 32.4 ± 7.2, 38.1 ± 13.3, 42.9 ± 5.4, and 69.3 ± 35.9 h (n = 3 or 4, 95% confidence level), respectively. The viability of cells in all experiments was above 90%, i.e., while increased CO2 concentrations inhibited cell growth, it did not affect cell viability. The osmolality for all bioreactor experiments was observed to be 300–360 mOsm/kg, a range that is known to have a negligible effect on insect cell culture. Elevated CO2 concentration did not significantly alter the cell specific glucose consumption rate (2.5–3.2 × 10?17 mol/cell s), but slightly increased the specific lactate production rate from ?3.0 × 10?19 to 10.2 × 10?19 mol/cell s. Oxidative stress did not contribute to CO2 inhibition in uninfected Sf‐9 cells as no significant increase in the levels of lipid hydroperoxide and protein carbonyl concentrations was discovered at elevated CO2 concentration. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:465–469, 2016 相似文献
5.
Various physiological characteristics of photosynthesis in the unicellular red alga Porphyridium cruentum Naegeli have been investigated. The rate of photosynthesis was optimal at 25° C and pH 7.5 and was not inhibited by 21% oxygen over a temperature range of 5 to 35° C. Kinetics of whole cell photosynthesis as a function of substrate concentration gave a K1/2, (CO2) of 0.3 μM. CO2 compensation point, measured in a closed system at pH 7.5, was a constant 6.7 m?L · L?1 over the temperature range 15 to 30° C and was unaffected by O2 concentration. Whole cell photosynthesis, measured in a closed system at alkaline pH, showed that the rates of oxygen evolution were greatly in excess of the rate of CO2 supply from the spontaneous dehydration of HCO3? in the medium. This indicates that bicarbonate is utilized by the cell to support this photosynthetic rate. These physiological characteristics of Porphyridium cruentum are consistent with the hypothesis that this alga transports bicarbonate across the plasmalemma. 相似文献
6.
Assaf Sukenik Dan Tchernov Aaron Kaplan Emma Huertas Luis M. Lubian Alexander Livne 《Journal of phycology》1997,33(6):969-974
Uptake, efflux and utilization of inorganic carbon were investigated in the marine eustigmatophyte Nannochloropsis sp. grown under an air level of CO2. Maximal photosynthetic rate was hardly affected by raising the pH porn 5.0 to 9.0. The apparent photosynthetic affinity for dissolved inorganic carbon (DIC) was 35 μM DIC between pH 6.5 to 9.0, but increased approximately threefold at pH 5.0 suggesting that HCO3- was the main DIC species used from the medium. No external carbonic anhydrase (CA) activity could be detected by the pH drift method. However, application of ethoxyzolamide (an inhibitor of CA) resulted an a significant inhibition of photosynthetic O2 evolution and carbon utilization, suggesting involvement of internal CA or CA-like activity in DIC utilization. Under high light conditions, the rate of HCO3? uptake and its internal conversion to CO2 apparently exceeded the rate of carbon fixation, resulting in a large leak of CO2 from the cells to the external medium. When the cells were exposed to low DIC concentrations, the ratio of internal to external DIC concentration was about eight. On the other hand, in the presence of 2 mM DIC, conditions prevailing in the marine environment, the internal concentration of DIC was only 50% higher than the external one. 相似文献
7.
Thalli of Ulva reticulata Forskaal, Ulva rigida C. Ag., and Ulva pulchra Jaasund were incubated at different concentrations of dissolved CO2. Incubation at a high CO2 concentration resulted in decreased oxygen evolution rate and lower affinity for inorganic carbon at high pH conditions, i.e. the ability to use HCO3– as a carbon source was reduced. This effect was reversible, and plants regained this HCO3– uptake capacity when transferred to air concentrations of CO2. The phytosynthetic oxygen evolution rate of plants grown at high CO2 concentration was reduced by high O2 concentrations, whereas thalli and protoplasts from cultures grown at air concentration were not affected. This is interpreted as a deactivation of the carbon-concentrating mechanism during conditions of high CO2 resulting in high photorespiration when plants are exposed to high O2 concentrations. Protoplasts were not affected by high O2 to the same extent and were not able to utilize HCO3– from the medium. The algae were able to grow at very low CO2 concentrations, but growth was suppressed when an inhibitor of external carbonic anhydrase was present. Assay of carbonic anhydrase activities showed that external and internal CA activities were lower in plants grown at a high CO2 concentration compared to plants grown at a low concentration of CO2. Possible mechanisms for HCO3– utilization in these Ulva species are discussed. 相似文献
8.
The processes of CO2 acquisition were characterized for the acid‐tolerant, free‐living chlorophyte alga, CPCC 508. rDNA data indicate an affiliation to the genus Coccomyxa, but distinct from other known members of the genus. The alga grows over a wide range of pH from 3.0 to 9.0. External carbonic anhydrase (CA) was detected in cells grown above pH 5, with the activity increasing marginally from pH 7 to 9, but most of the CA activity was internal. The capacity for HCO3? uptake of cells treated with the CA inhibitor acetazolamide (AZA), was investigated by comparing the calculated rate of uncatalyzed CO2 formation with the rate of photosynthesis. Active bicarbonate transport occurred in cells grown in media above pH 7.0. Monitoring CO2 uptake and O2 evolution by membrane‐inlet mass spectrometry demonstrated that air‐grown cells reduced the CO2 concentration in the medium to an equilibrium concentration of 15 μM, but AZA‐treated cells caused a drop in extracellular CO2 concentration to a compensation concentration of 27 μM at pH 8.0. CO2‐pulsing experiments with cells in the light indicated that the cells do not actively take up CO2. An internal pool of unfixed inorganic carbon was not detected at the CO2 compensation concentration, probably because of the lack of active CO2 uptake, but was detectable at times before compensation point was reached. These results indicate that this free‐living Coccomyxa possesses a CO2‐concentrating mechanism (CCM) due to an active bicarbonate‐uptake system, unlike the Coccomyxa sp. occurring in symbiotic association with lichens. 相似文献
9.
Peng Jin Kunshan Gao John Beardall 《Evolution; international journal of organic evolution》2013,67(7):1869-1878
The ongoing ocean acidification associated with a changing carbonate system may impose profound effects on marine planktonic calcifiers. Here, we show that a coccolithophore, Gephyrocapsa oceanica, evolved in response to an elevated CO2 concentration of 1000 μatm (pH reduced to 7.8) in a long‐term (~670 generations) selection experiment. The high CO2‐selected cells showed increases in photosynthetic carbon fixation, growth rate, cellular particulate organic carbon (POC) or nitrogen (PON) production, and a decrease in C:N elemental ratio, indicating a greater upregulation of PON than of POC production under the ocean acidification condition. Cells from the low CO2 selection process shifted to high CO2 exposure showed an enhanced cellular POC and PON production rates. Our data suggest that the coccolithophorid could adapt to ocean acidification with enhanced assimilations of carbon and nitrogen but decreased C:N ratios. 相似文献
10.
Brain cortex slices from fed, 48 h and 120 h fasted rats were incubated and 14CO2 was measured from (a) [U-14C]glucose (5 mm ) either alone or in the presence of l -lcucine (0.1 or 1 mm ), and (b) [U-14C]leucine or [l-14C]leucine at 0.1 or 1 mm with or without glucose (5 mm ). In other experiments, sodium dl -3-hydroxybutyrate (3-OHB) or acetoacetate (AcAc) at 1 or 5 mm were added in the above incubation mixture. The rate of conversion of [U14C]glucose to CO2 was decreased 20% by leucine at 1 mm and 30–50% by 3-OHB at 1 or 5 mm but not by leucine at 0.1 mm . The effects of 3-OHB and of leucine (1 mm ) were not additive. The effects of leucine were similar in the fed and fasted rats. The rate of conversion of [U-14C]leucine or [l-,4C]leucine to 14CO2 at 0.1 mm and 1.0 mm was increased by glucose (35%) in the fed or fasted rats. Ketone bodies in the absence of glucose had no effect on leucine oxidation. However, the stimulatory effect of glucose on the rate of conversion of leucine to CO2 was inhibited by 3-OHB at 5 mm . These results suggest that (a) leucine in increased concentrations (1 mm ) may reduce glucose oxidation by brain cortex while itself becoming an oxidative fuel for brain, and (b) leucine oxidation by brain may be influenced by the prevailing glucose and ketone concentrations. 相似文献
11.
Inorganic Carbon Source for Photosynthesis in the Seagrass Thalassia hemprichii (Ehrenb.) Aschers 总被引:1,自引:0,他引:1
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Abel KM 《Plant physiology》1984,76(3):776-781
Photosynthetic carbon uptake of the tropical seagrass Thalassia hemprichii (Ehrenb.) Aschers was studied by several methods. Photosynthesis in buffered seawater in media in the range of pH 6 to pH 9 showed an exponentially increasing rate with decreasing pH, thus indicating that free CO2 was a photosynthetic substrate. However, these experiments were unable to determine whether photosynthesis at alkaline pH also contained some component due to HCO3− uptake. This aspect was further investigated by studying photosynthetic rates in a number of media of varying pH (7.8-8.61) and total inorganic carbon (0.75-13.17 millimolar). In these media, photosynthetic rate was correlated with free CO2 concentration and was independent of the HCO3− concentration in the medium. Short time-course experiments were conducted during equilibration of free CO2 and HCO3− after injection of 14C labeled solution at acid or alkaline pH. High initial photosynthetic rates were observed when acidic solutions (largely free CO2) were used but not with alkaline solutions. The concentration of free CO2 was found to be a limiting factor for photosynthesis in this plant. 相似文献
12.
THE EFFECT OF pH ON GROWTH, PROTEIN SYNTHESIS, AND LIPID-RICH PARTICLES OF CULTURED MAMMALIAN CELLS 总被引:4,自引:2,他引:2
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A simple procedure has been established for controlling and measuring the pH of media in which the bicarbonate-carbonic acid system is the predominant buffer. The HCO-3 concentration was maintained at 22.5 mM and the H2CO3 concentration was varied by equilibrating the media with 0.5 to 40 per cent CO2 in air. The curve relating extracellular pH to 3 day cell growth was similar for glass-attached HeLa and Chang liver cells. Maximum growth occurred over a pH range of 7.38 to 7.87. Cell growth declined precipitously on the alkaline side and more gradually on the acid side of the optimal pH range. Comparable pH growth curves were also obtained with newly isolated cells from rat liver and skeletal muscle. It was shown that the effect of pH on growth was independent of the CO2 concentration and that the essential nutrients in the medium were stable over the pH range studied. Although alkalosis depressed the 3 day cell population, cells exposed to a pH of 8.0 to 8.2 grew at the maximal rate for the first 12 to 24 hours. Growth then ceased abruptly and the cells entered a steady state with respect to net protein synthesis. This was followed by cytoplasmic retraction and cell death. Increasing the concentrations of calcium or magnesium in the medium failed to prevent the effects of alkalosis. Moreover, the increase in CO-3 concentration of the media and the concomitant decrease in Ca++ ion concentration that occur at high pH were eliminated as determining factors in the growth failure and death. While acidosis had a less pronounced effect on the 3 day cell population, its effect on the growth rate was immediate. The increase in cell generation time was proportional to the H+ ion concentration. In each of the cell lines studied, acidosis was accompanied by a striking increase in the number of cytoplasmic perinuclear granules. These granules which stain supravitally with Janus green are extracted from fixed cells with lipid solvents. They maintain their identity in cell homogenates and may be isolated from the other subcellular structures by differential centrifugation; at 100,000 g they form a distinct layer at the top of the supernatant fraction. On the basis of their physical and chemical properties, these granules have been called lipid-rich particles. The accumulation of lipid-rich particles in acidosis was independent of the growth rate and the CO2 concentration. 相似文献
13.
Manure slurries (n = 3) prepared from the feces and urine of lactating dairy cattle (1 part urine, 2.2 parts feces, and 6.8
parts distilled water) had an initial pH of 8.6 ± 0.1; dissolved carbonate concentrations of 48 ± 4 mm, and Escherichia coli counts of 5.9 ± 0.7 logs per ml slurry. The pH of untreated slurries declined to pH 7.0 ± 0.1 by the 10th day of incubation,
and the E. coli count increased approximately 10-fold (P < 0.05). When slurries were treated with Na2CO3, K2CO3, NaHCO3 or Na2CO3·NaHCO3 (0 to 16 g/kg slurry), the dissolved carbonates increased in a linear fashion, but only Na2CO3 and K2CO3 (8 g/kg or greater) or Na2CO3·NaHCO3 (16 g/kg) ensured an alkaline pH. Even relatively low concentrations of Na2CO3 or K2CO3 (8 or 12 g/kg) caused a decrease in E. coli viability (P < 0.05), and E. coli could not be detected if 16 g/kg was added (day 5 or 10 of incubation). Na2CO3·NaHCO3 also caused a decrease in E. coli viability, (P < 0.05), but some E. coli (approximately 104 cells per g) were detected on day 10 even if the concentration was 16 g/kg. NaHCO3 did not prevent the decrease in pH or cause a decrease in E. coli numbers (P > 0.05). Calculations based on the Henderson-Hasselbalch equation (pH and dissolved carbonates) indicated that little E. coli killing was noted until the dissolved carbonate anion concentrations (CO3
−2) were greater than 1 mm, but bicarbonate anion (HCO3
−) concentrations as high as 180 mm did not affect E. coli viability. These results are consistent with the idea that carbonate anion has antimicrobial properties and can kill E. coli in dairy cattle manure.
Received: 20 December 2000 / Accepted: 7 February 2001 相似文献
14.
Dalin Shi Haizheng Hong Xi Su Lirong Liao Siwei Chang Wenfang Lin 《Journal of phycology》2019,55(3):521-533
Although increasing the pCO2 for diatoms will presumably down‐regulate the CO2‐concentrating mechanism (CCM) to save energy for growth, different species have been reported to respond differently to ocean acidification (OA). To better understand their growth responses to OA, we acclimated the diatoms Thalassiosira pseudonana, Phaeodactylum tricornutum, and Chaetoceros muelleri to ambient (pCO2 400 μatm, pH 8.1), carbonated (pCO2 800 μatm, pH 8.1), acidified (pCO2 400 μatm, pH 7.8), and OA (pCO2 800 μatm, pH 7.8) conditions and investigated how seawater pCO2 and pH affect their CCMs, photosynthesis, and respiration both individually and jointly. In all three diatoms, carbonation down‐regulated the CCMs, while acidification increased both the photosynthetic carbon fixation rate and the fraction of CO2 as the inorganic carbon source. The positive OA effect on photosynthetic carbon fixation was more pronounced in C. muelleri, which had a relatively lower photosynthetic affinity for CO2, than in either T. pseudonana or P. tricornutum. In response to OA, T. pseudonana increased respiration for active disposal of H+ to maintain its intracellular pH, whereas P. tricornutum and C. muelleri retained their respiration rate but lowered the intracellular pH to maintain the cross‐membrane electrochemical gradient for H+ efflux. As the net result of changes in photosynthesis and respiration, growth enhancement to OA of the three diatoms followed the order of C. muelleri > P. tricornutum > T. pseudonana. This study demonstrates that elucidating the separate and joint impacts of increased pCO2 and decreased pH aids the mechanistic understanding of OA effects on diatoms in the future, acidified oceans. 相似文献
15.
Inorganic carbon acquisition has been investigated in the marine haptophyte Isochrysis galbana. External carbonic anhydrase (CA) was present in air‐grown (0.034% CO2) cells but completely repressed in high (3%) CO2‐grown cells. External CA was not inhibited by 1.0 mM acetazolamide. The capacity of cells to take up bicarbonate was examined by comparing the rate of photosynthetic O2 evolution with the calculated rate of spontaneous CO2 supply; at pH 8.2 the rates of O2 evolution exceeded the CO2 supply rate 14‐fold, indicating that this alga was able to take up HCO3 ? . Monitoring CO2 concentrations by mass spectrometry showed that suspensions of high CO2‐grown cells caused a rapid drop in the extracellular CO2 in the light and addition of bovine CA raised the CO2 concentration by restoring the HCO3 ? ‐CO2 equilibrium, indicating that cells were maintaining the CO2 in the medium below its equilibrium value during photosynthesis. A rapid increase in extracellular CO2 concentration occurred on darkening the cells, indicating that the cells had accumulated an internal pool of unfixed inorganic carbon. Active CO2 uptake was blocked by the photosynthetic electron transport inhibitor 3‐(3′,4′‐dichlorphenyl)‐1,1‐dimethylurea, indicating that CO2 transport was supported by photosynthetic reactions. These results demonstrate that this species has the capacity to take up HCO3 ? and CO2 actively as sources of substrate for photosynthesis and that inorganic carbon transport is not repressed by growth on high CO2, although external CA expression is regulated by CO2 concentration. 相似文献
16.
Filtrates (conditioned medium) from high-density Chlorella vulgaris cultures in photobioreactors were obtained and tested for autoinhibitory activity under different conditions. Exponentially growing cells were inoculated at low initial cell concentration (2 × 105 cells/ml) in 90% conditioned medium (CM) supplemented with 10% fresh medium (FM) at low (atmospheric) CO2 levels. The time sequence of DNA histograms of cells in CM cultures showed that there is an accumulation of cells with two and four DNA equivalents in the culture over a period of time, signifying a blockage of cells at the division stage of the cell cycle. Examination of the chemical composition of CM showed the presence of high concentrations (> 10 mM) of bicarbonate. Adding similar bicarbonate concentrations to FM were found to have similar effects as CM cultures, causing blockage of cell division, though the intensity of the blocking effect was lower. The bicarbonate-free CM did not show any cell cycle modulating or inhibitory activity. The growth of cells cultivated at high (5%) CO2 levels in 90% CM supplemented with 10% FM was comparable to 10% FM cultures, indicating nutrient limitation in 90% CM culture. When the 90% CM culture was supplemented with 100% nutrients, the growth rate and final cell concentration was similar to 100% FM culture. Based on these results we conclude that C. vulgaris does not secrete any autoinhibitor(s) or cell cycle modulating compound(s) under the conditions from which the CM was obtained. 相似文献
17.
Mass spectrometry was used to investigate the uptake of CO2 in Eremosphaera viridis DeBary. Upon illumination, cells preincubated at pH 7.5 with 100 M dissolved inorganic carbon (DIC) rapidly depleted almost all the free CO2 from the medium. Rapid equilibrium between HCO
3
-
and CO2 occurred upon addition of bovine carbonic anhydrase (CA) to the medium, showing that CO2 depletion resulted from a selective uptake of CO2 rather than an uptake of all inorganic carbon species. Glycolaldehyde (10 mM) completely inhibited CO2 fixation but had little effect on CO2 transport. Transfer of glycolaldehyde-treated cells to the dark caused a rapid efflux of CO2 from the unfixed intracellular DIC pool which was found to be at least threeto sixfold higher in concentration than that of the external medium. These results indicate that E. viridis actively transports CO2 against a concentration gradient. No external CA was detected in these cells either by potentiometric or mass-spectrometric assay. In the absence of external CA, the rate of photosynthetic O2 evolution in the pH range 7.5 to 8.0 did not exceed the calculated rate of CO2 supply, indicating a limited capacity for HCO2 uptake in these cells. Electrophysiological measurements indicate that CO2 uptake is electrically silent and thus is not a consequence of H+-CO2 symport activity. Microsomal membranes isolated from Eremosphaera showed ATPase activity which was enhanced by CO2. These results indicate that active CO2 uptake is mediated by an ATPase.Abbreviations BTP
1,3-bis[tris(hydroximethyl)-methylamino]-propane
- CA
carbonic anhydrase
- Chl
chlorophyll
- DIC
dissolved inorganic carbon
- [14C]DMO
5,5-dimethyl-[2-14C]-oxaz-didine-2,4-dione
- WA
Wilbur-Anderson units
This work was supported by grants to B.C. and R.R.L. from the Natural Sciences and Engineering Research Council of Canada. We thank the Department of Biology, Queen's University, Kingston, Ontario for the use of the mass-spectrometer facility. We are indebted to A.G. Miller for his expert advice on operating the mass spectrometer and to Ms. Shahebina Samji for running the Bradford assays. 相似文献
18.
Carbon uptake in the green macroalga Cladophora glomerata (L.) Kütz. from the brackish Baltic Sea was studied by recording changes in pH, alkalinity, and inorganic carbon concentration of the seawater medium during photosynthesis. The use of specific inhibitors identified three uptake mechanisms: 1) dehydration of HCO3 ? into CO2 by periplasmic carbonic anhydrase, followed by diffusion of CO2 into the cell; 2) direct uptake of HCO3 ? via a 4,4′‐diisothiocyanato‐stilbene‐2,2′‐disulfonate‐sensitive mechanism; and 3) uptake of inorganic carbon by the involvement of a vanadate‐sensitive P‐type H + ‐ATPase (proton pump). A decrease in the alkalinity of the seawater medium during carbon uptake, except when treated with vanadate, indicated a net uptake of the ionic species contributing to alkalinity (i.e. HCO3 ? , CO32 ? , and OH ? ) from the medium, where OH ? influx is equivalent to H + efflux. This would suggest that the proton pump is involved in HCO3 ? transport. We also show that the proton pump can be induced by carbon limitation. The inducibility of carbon uptake in C. glomerata may partly explain why this species is so successful in the upper littoral zone of the Baltic Sea. Usually, carbon limitation is not a problem in the upper littoral of the sea. However, it may occur frequently within dense Cladophora belts with high photosynthetic rates that create high pH and low carbon concentrations in the alga's microenvironment. 相似文献
19.
KINETICS OF THE SODIUM-DEPENDENT TRANSPORT OF GAMMA-AMINOBUTYRIC ACID BY SYNAPTOSOMES 总被引:17,自引:12,他引:5
D. L. Martin 《Journal of neurochemistry》1973,21(2):345-356
The kinetics of transport of gamma-aminobutyric acid [2,3-3H] by synaptosomes from rat brain was studied by means of a rapid filtration technique. The rate of uptake was proportional to the protein concentration over the range 0.05—0.2 mg of synaptosomal protein per ml. Although apparent allosteric kinetics were observed with sodium, transport followed simple saturation kinetics with respect to GABA and no heterotropic, cooperative effects of GABA on sodium on kinetics were observed. A minimum of three interacting sodium sites is suggested the basis of Hill plots of the sodium data. Both the apparent Km and Vmax for GABA were functions of the sodium ion concentration but the effect of sodium was considerably greater on Vmax than on the apparent Km The Vmax for GABA was 1.1 ± 0.5 nmol.min?1 mg?1 of protein at 95 mm sodium and decreased to 12 per Cent of this value at 19 mm sodium. The apparent Km for GABA increased from 4.0 ± 1.0 μm at 95 mm sodium to 8.4 ± 2.0 μm at 19 mm sodium. Potassium was a noncompetitive inhibitor with respect to GABA and did not affect the apparent cooperativity observed with sodium. These findings are discussed in terms of models of GABA transport. 相似文献
20.
The mechanism of inorganic carbon (Ci) acquisition by the economic brown macroalga, Hizikia fusiforme (Harv.) Okamura (Sargassaceae), was investigated to characterize its photosynthetic physiology. Both intracellular and extracellular carbonic anhydrase (CA) were detected, with the external CA activity accounting for about 5% of the total. Hizikia fusiforme showed higher rates of photosynthetic oxygen evolution at alkaline pH than those theoretically derived from the rates of uncatalyzed CO2 production from bicarbonate and exhibited a high pH compensation point (pH 9.66). The external CA inhibitor, acetazolamide, significantly depressed the photosynthetic oxygen evolution, whereas the anion‐exchanger inhibitor 4,4′‐diisothiocyano‐stilbene‐2,2′‐disulfonate had no inhibitory effect on it, implying the alga was capable of using HCO3? as a source of Ci for its photosynthesis via the mediation of the external CA. CO2 concentrations in the culture media affected its photosynthetic properties. A high level of CO2 (10,000 ppmv) resulted in a decrease in the external CA activity; however, a low CO2 level (20 ppmv) led to no changes in the external CA activity but raised the intracellular CA activity. Parallel to the reduction in the external CA activity at the high CO2 was a reduction in the photosynthetic CO2 affinity. Decreased activity of the external CA in the high CO2 grown samples led to reduced sensitiveness of photosynthesis to the addition of acetazolamide at alkaline pH. It was clearly indicated that H. fusiforme, which showed CO2‐limited photosynthesis with the half‐saturating concentration of Ci exceeding that of seawater, did not operate active HCO3? uptake but used it via the extracellular CA for its photosynthetic carbon fixation. 相似文献