Inorganic carbon acquisition and its energization in eustigmatophyte algae

The eustigmatophyceans are primitive unicellular algae that represent the most basal group of ochrophytes. They are believed to be obligate photoautotrophs, occurring mainly in freshwater and soil but with some marine representatives. The freshwater eustigmatophytes Monodus subterraneus and Vischeria stellata, and the marine eustigmatophyte Nannochloropsis gaditana, have been studied by mass spectrometry with respect to their characteristics for inorganic carbon (Ci) uptake. A CO2 concentrating mechanism was found in all three, but an external carbonic anhydrase (CA) was not detected. The acquisition of Ci from the external medium was based on the active transport of HCO3–, CO2, or both. In particular, N. gaditana was able to use HCO3– exclusively as an exogenous carbon source for photosynthesis, with this HCO3– being subsequently converted to CO2 by an intracellular CA for photosynthetic fixation. A unique characteristic of this species was its capacity to transport HCO3– during prolonged periods of time in the dark. In contrast, M. subterraneus utilized CO2 alone through an active transport process, whereas V. stellataexhibited the capacity to transport both HCO3– and CO2. The uptake of CO2 also continued in the dark in V. stellatacells. Regardless of the Ci species taken up, transport was abolished by anoxia and by inhibitors of mitochondrial respiration. These results indicate that that the supply of Ci for photosynthetic CO2 fixation is partly dependent upon mitochondrial activity in these primitive eukaryotes.

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A nuclear localization signal can enhance both the nuclear transport and expression of 1 kb DNA

Journal of Cell Science ◽

10.1242/jcs.112.12.2033 ◽

1999 ◽

Vol 112 (12) ◽

pp. 2033-2041

Author(s):

J.J. Ludtke ◽

G. Zhang ◽

M.G. Sebestyen ◽

J.A. Wolff

Keyword(s):

Active Transport ◽

Nuclear Localization ◽

Transport Process ◽

Nuclear Transport ◽

Passive Diffusion ◽

Viral Gene ◽

Nuclear Localization Signals ◽

Size Limit ◽

Cytosolic Extract ◽

Active Transport Process

Although the entry of DNA into the nucleus is a crucial step of non-viral gene delivery, fundamental features of this transport process have remained unexplored. This study analyzed the effect of linear double stranded DNA size on its passive diffusion, its active transport and its NLS-assisted transport. The size limit for passive diffusion was found to be between 200 and 310 bp. DNA of 310–1500 bp entered the nuclei of digitonin treated cells in the absence of cytosolic extract by an active transport process. Both the size limit and the intensity of DNA nuclear transport could be increased by the attachment of strong nuclear localization signals. Conjugation of a 900 bp expression cassette to nuclear localization signals increased both its nuclear entry and expression in microinjected, living cells.

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Total contents and net movements of magnesium in the rat uterus

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1971.220.6.2067-r ◽

1971 ◽

Vol 220 (6) ◽

pp. 2067-2067

Author(s):

A. H. Moawad ◽

E. E. Daniel

Keyword(s):

Membrane Potential ◽

Active Transport ◽

Extracellular Space ◽

Transport Process ◽

Electrochemical Gradient ◽

Rat Uterus ◽

Active Transport Process

Page 75: A. H. Moawad and E. E. Daniel. "Total contents and net movements of magnesium in the rat uterus." Page 80, column 2, line 44, involving the calculation of Vm the answer to the equation, –0.067 V, should read, "–0.012 V." Page 80, column 2, lines 49–54 should read, "The calculated magnesium equilibrum potential is less than the observed membrane potential, which is about 0.050 V. Therefore, some of the tissue magnesium may be excluded by an active transport process against an electrochemical gradient or by loose binding in the extracellular space."

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Ionic regulation of Na absorption in proximal colon: cation inhibition of electroneutral Na absorption

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1987.252.1.g100 ◽

1987 ◽

Vol 252 (1) ◽

pp. G100-G108

Author(s):

J. H. Sellin ◽

R. De Soignie

Keyword(s):

Linear Function ◽

Active Transport ◽

Transport Process ◽

Proximal Colon ◽

High Rate ◽

Ionic Regulation ◽

Diffusional Flux ◽

Active Transport Process

Active Na absorption (JNanet) in rabbit proximal colon in vitro is paradoxically stimulated as [Na] in the bathing media is lowered with constant osmolarity. At 140 mM [Na]o, JNanet is -0.6 +/- 0.4 mueq X cm-2 X h-1, whereas at 50 mM [Na]o JNanet is 5.0 +/- 0.7 mueq X cm-2 X h-1, P less than 0.01. JNas----m is a linear function of [Na]o, suggesting a diffusional flux. JNam----s increases almost linearly from 0 to 50 mM [Na]o but then plateaus and actually decreases from 50 to 140 mM [Na]o, consistent with inhibition of an active transport process. Both lithium and Na are equally effective inhibitors of JNanet, whereas choline and mannitol do not block the high rate of JNanet observed in decreased [Na]o. Either gluconate or proprionate replacement of Cl inhibits JNanet. Removal of K or HCO3 does not alter Na absorption. JNanet at lowered [Na]o is electrically silent and is accompanied by increased Cl absorption; it is inhibited by 10(-3) M amiloride and 10(-3) M theophylline but not by 10(-4) M bumetanide. Epinephrine is equally effective at stimulating Na absorption at 50 and 140 mM [Na]; yohimbine does not inhibit JNanet at 50 mM [Na]o. Na gradient experiments are consistent with a predominantly serosal effect of the decreased [Na]o. These results suggest that Na absorption in rabbit proximal colon in vitro is stimulated by decreased [Na]; the effect is cation specific, both Na and Li blocking the stimulatory effect.(ABSTRACT TRUNCATED AT 250 WORDS)

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Active Transport of Inorganic Carbon Increases the Rate of O2 Photoreduction by the Cyanobacterium Synechococcus UTEX 625

PLANT PHYSIOLOGY ◽

10.1104/pp.88.1.6 ◽

1988 ◽

Vol 88 (1) ◽

pp. 6-9 ◽

Cited By ~ 31

Author(s):

Anthony G. Miller ◽

George S. Espie ◽

David T. Canvin

Keyword(s):

Active Transport ◽

Inorganic Carbon

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Biochemical Studies on Active Transport

The Journal of General Physiology ◽

10.1085/jgp.52.1.279 ◽

1968 ◽

Vol 52 (1) ◽

pp. 279-295 ◽

Cited By ~ 12

Author(s):

Arthur B. Pardee

Keyword(s):

Active Transport ◽

Cell Function ◽

Specific Protein ◽

Transport Systems ◽

Initial State ◽

Intact Cells ◽

The Past ◽

Biochemical Studies ◽

Active Transport Process

The active transport process, so important in cell function, has been studied in the past with intact cells. Models which have arisen from this work all depend on: first, a specific protein to recognize the substrate; second, translocation of the substrate across the cell membrane; third, release of substrate within the cell and restoration of the system to its initial state. These steps are adequate for facilitated transport, but in active transport an energy input is required to maintain a concentration gradient. Parts of transport systems have been isolated recently. A protein which specifically recognizes ß-galactosides has been partially purified. In another case, a protein that appears to be the recognition part of the sulfate transport system of Salmonella typhimurium has been crystallized, and many of its properties have been described. The role of this protein in recognition and in translocation is discussed. Also proteins that phosphorylate a variety of sugars as they enter the cell's interior provide a mechanism for concentrating sugars as their phosphates, against a gradient.

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Physiological aspects of CO2 and HCO3− transport by cyanobacteria: a review

Canadian Journal of Botany ◽

10.1139/b90-165 ◽

1990 ◽

Vol 68 (6) ◽

pp. 1291-1302 ◽

Cited By ~ 98

Author(s):

Anthony G. Miller ◽

George S. Espie ◽

David T. Canvin

Keyword(s):

Active Transport ◽

Inorganic Carbon ◽

Dissolved Inorganic Carbon ◽

Structural Analog ◽

Transport Systems ◽

Ribulose Bisphosphate Carboxylase ◽

High Concentration ◽

Bisphosphate Carboxylase ◽

Ribulose Bisphosphate Carboxylase Oxygenase ◽

Inorganic Carbon Transport

Cyanobacteria grown at air levels of CO2, or lower, have a very high photosynthetic affinity for CO2. For ceils grown in carbon-limited chemostats at pH 9.6, the K0.5 (CO2) for whole cell CO2 fixation is about 3 nM. This is in spite of a K0.5 (CO2) for cyanobacterial ribulose bisphosphate carboxylase/oxygenase of about 200 μM. It is now clear that cyanobacteria can photosynthesize at very low CO2 concentrations because they raise the CO2 concentration dramatically around the carboxylase. This rise in the intracellular CO2 concentration involves the active transport of HCO3− and CO2, perhaps by separate transport systems. The transport of HCO3− often requires millimolar levels of Na+, and this provides a ready means of initiating HCO3− transport. The active transport of CO2 requires only micromolar levels of Na+. In the rather dense cell suspensions used in transport studies the extent of CO2 uptake is often limited by the rate at which CO2 can be formed from the HCO3− in the medium. The addition of carbonic anhydrase relieves this kinetic limitation on CO2 transport. The active transport of CO2 can be selectively inhibited by the structural analog carbon oxysulfide (COS). When HCO3− transport is allowed in the presence of COS there is a substantial net leakage of CO2 from the cells. This leaked CO2 results from the intracellular dehydration of the accumulated HCO3−. This CO2 is normally scavenged by the active CO2 pump. If cells are allowed to transport H13C18O18O18O− for 5 s and if CO2 transport is suddenly quenched by the addition of COS, then a rapid leakage of 13C16O16O occurs. If the rapidly released CO2 was actually present in the cells before the addition of the COS, then the intracellular CO2 concentration would have been about 0.6 mM. Not only is this a high concentration, but since the leaked CO2 was completely depleted of the initial 18O, it must have been in rapid equilibrium with the total dissolved inorganic carbon within the cells. Cells grown on high levels of inorganic carbon, either as CO2 or HCO3−, lack the active HCO3− system but still retain a capacity, albeit reduced, for CO2 transport. Cyanobacteria seem to adjust their complement of inorganic carbon transport systems so that the K0.5 for transport is close to the inorganic carbon concentration of the growth medium.

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Glycolaldehyde Inhibits CO2 Fixation in the Cyanobacterium Synechococcus UTEX 625 without Inhibiting the Accumulation of Inorganic Carbon or the Associated Quenching of Chlorophyll a Fluorescence

PLANT PHYSIOLOGY ◽

10.1104/pp.91.3.1044 ◽

1989 ◽

Vol 91 (3) ◽

pp. 1044-1049 ◽

Cited By ~ 36

Author(s):

Anthony G. Miller ◽

David T. Canvin

Keyword(s):

Chlorophyll A ◽

Chlorophyll A Fluorescence ◽

Co2 Fixation ◽

Inorganic Carbon

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Ouabain modulation of cellular calcium stores and signaling

AJP Renal Physiology ◽

10.1152/ajprenal.00251.2007 ◽

2007 ◽

Vol 293 (5) ◽

pp. F1518-F1532 ◽

Cited By ~ 16

Author(s):

Aurélie Edwards ◽

Thomas L. Pallone

Keyword(s):

Mathematical Model ◽

Sarcoplasmic Reticulum ◽

Active Transport ◽

Intracellular Localization ◽

Calcium Stores ◽

Model Simulations ◽

Store Depletion ◽

Intracellular Ca ◽

Atpase Inhibition ◽

Predominant Effect

Ouabain-like factors modulate intracellular Ca2+ concentrations and Ca2+ stores. Recently, a role for Na+-K+-ATPase Na+ transport inhibition as a pivotal event in ouabain signaling was questioned (Kaunitz JD. Am J Physiol Renal Physiol 290: F995–F996, 2006). In the present study, we used a mathematical model of Ca2+ trafficking in cytoplasm and subplasmalemmal microdomains to simulate the pathways through which ouabain can affect Ca2+ signaling: inhibition of active transport by Na+-K+-ATPase α1- and α2-isoforms, activation of inositol trisphosphate (IP3) production, and increased IP3 receptor (IP3R) conductance. A fundamental prediction is that Na+-K+-ATPase inhibition favors sarcoplasmic reticulum Ca2+ store loading, whereas Src-mediated increases in IP3 production and IP3R sensitization favor store depletion. The model predicts that α2-isoform inhibition generates a peak-and-plateau pattern of cytosolic Ca2+ concentration ([Ca2+]cyt) elevation, whereas α1-isoform inhibition yields a monophasic rise. The effects of ouabain-mediated increases in IP3 production or IP3R conductance on [Ca2+]cyt depend on their relative distributions between cellular microdomains and the bulk cytoplasm. Simulations suggest that the intracellular localization of IP3 production is a pivotal determinant of the changes in compartmental Ca2+ concentrations that can be induced by ouabain. As a consequence of sequestration of the ouabain-sensitive α2-isoform into microdomains, inhibition of the α2-isoform in rodents is not predicted to significantly affect cytosolic Na+ concentration. Model simulations support the hypothesis that ouabain can enhance agonist-evoked [Ca2+]cyt transients when its predominant effect is to inhibit α2-isoform Na+ transport and, thereby, increase Ca2+ loading into sarcoplasmic reticulum stores.

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