scholarly journals Phosphate-dependent regulation of the low- and high-affinity transport systems in the model actinomycete Streptomyces coelicolor

Microbiology ◽  
2008 ◽  
Vol 154 (8) ◽  
pp. 2356-2370 ◽  
Author(s):  
Fernando Santos-Beneit ◽  
Antonio Rodríguez-García ◽  
Etelvina Franco-Domínguez ◽  
Juan F. Martín
Keyword(s):  
Streptomyces Coelicolor ◽  
Transport Systems ◽  
High Affinity

scholarly journals The STK2 gene, which encodes a putative Ser/Thr protein kinase, is required for high-affinity spermidine transport in Saccharomyces cerevisiae.

1997 ◽  
Vol 17 (6) ◽  
pp. 2994-3004 ◽  
Author(s):  
M Kaouass ◽  
M Audette ◽  
D Ramotar ◽  
S Verma ◽  
D De Montigny ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Protein Kinase ◽  
Fusion Gene ◽  
Transport Systems ◽  
Coding Region ◽  
Kinase Gene ◽  
Lower Affinity ◽  
High Affinity ◽  
Polyamine Transport ◽  
Exogenous Spermidine

Eukaryotic polyamine transport systems have not yet been characterized at the molecular level. We have used transposon mutagenesis to identify genes controlling polyamine transport in Saccharomyces cerevisiae. A haploid yeast strain was transformed with a genomic minitransposon- and lacZ-tagged library, and positive clones were selected for growth resistance to methylglyoxal bis(guanylhydrazone) (MGBG), a toxic polyamine analog. A 747-bp DNA fragment adjacent to the lacZ fusion gene rescued from one MGBG-resistant clone mapped to chromosome X within the coding region of a putative Ser/Thr protein kinase gene of previously unknown function (YJR059w, or STK2). A 304-amino-acid stretch comprising 11 of the 12 catalytic subdomains of Stk2p is approximately 83% homologous to the putative Pot1p/Kkt8p (Stk1p) protein kinase, a recently described activator of low-affinity spermine uptake in yeast. Saturable spermidine transport in stk2::lacZ mutants had an approximately fivefold-lower affinity and twofold-lower Vmax than in the parental strain. Transformation of stk2::lacZ cells with the STK2 gene cloned into a single-copy expression vector restored spermidine transport to wild-type levels. Single mutants lacking the catalytic kinase subdomains of STK1 exhibited normal parameters for the initial rate of spermidine transport but showed a time-dependent decrease in total polyamine accumulation and a low-level resistance to toxic polyamine analogs. Spermidine transport was repressed by prior incubation with exogenous spermidine. Exogenous polyamine deprivation also derepressed residual spermidine transport in stk2::lacZ mutants, but simultaneous disruption of STK1 and STK2 virtually abolished high-affinity spermidine transport under both repressed and derepressed conditions. On the other hand, putrescine uptake was also deficient in stk2::lacZ mutants but was not repressed by exogenous spermidine. Interestingly, stk2::lacZ mutants showed increased growth resistance to Li+ and Na+, suggesting a regulatory relationship between polyamine and monovalent inorganic cation transport. These results indicate that the putative STK2 Ser/Thr kinase gene is an essential determinant of high-affinity polyamine transport in yeast whereas its close homolog STK1 mostly affects a lower-affinity, low-capacity polyamine transport activity.

Proton gradient-dependent renal transport of glycine: evidence for vesicle studies

1990 ◽  
Vol 258 (2) ◽  
pp. F388-F396 ◽  
Author(s):  
H. Roigaard-Petersen ◽  
H. Jessen ◽  
S. Mollerup ◽  
K. E. Jorgensen ◽  
C. Jacobsen ◽  
...  
Keyword(s):  
Transport System ◽  
Membrane Vesicles ◽  
Proton Gradient ◽  
Transport Systems ◽  
Rabbit Kidney ◽  
Renal Transport ◽  
High Affinity ◽  
Luminal Membrane ◽  
Pars Recta ◽  
Pars Convoluta

The characteristics of renal transport of glycine by luminal membrane vesicles isolated from either proximal convoluted part (pars convoluta) or proximal straight part (pars recta) of rabbit proximal tubule were investigated. In vesicles from pars convoluta two transport systems have been characterized: a Na(+)-dependent system with intermediate affinity (half-saturation 3.64 mM) and a Na(+)-independent system that, in the presence of H+ gradient (extravesicular greater than intravesicular), can accelerate the transport of glycine into these vesicles. This is the first demonstration of H(+)-glycine cotransport across the luminal membrane of rabbit kidney proximal convoluted tubule. By contrast, in membrane vesicles from pars recta, transport of glycine was strictly dependent on Na+ and occurred via a dual transport system, namely a high-affinity (half-saturation 0.34 mM) and a low-affinity system (half-saturation 8.56 mM). The demonstration of competition between the H(+)-gradient dependent uptake of glycine, L-alanine, and L-proline, but insignificant inhibition with L-phenylalanine in vesicles from pars convoluta suggests that glycine, L-proline, and L-alanine probably share a common proton gradient-dependent transport system. In vesicles from pars recta, the Na(+)-dependent uptake of glycine was inhibited by low concentrations of L-alanine and L-phenylalanine, whereas addition of L-proline to the incubation medium did not significantly alter the uptake of glycine, suggesting that the Na(+)-dependent high-affinity system for glycine located in pars recta is shared with the high-affinity L-alanine and L-phenylalanine but not L-proline transport system.

D-glucose and L-leucine transport by human intestinal brush-border membrane vesicles

1989 ◽  
Vol 256 (3) ◽  
pp. G618-G623 ◽  
Author(s):  
J. M. Harig ◽  
J. A. Barry ◽  
V. M. Rajendran ◽  
K. H. Soergel ◽  
K. Ramaswamy
Keyword(s):  
Small Intestine ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Transport Systems ◽  
Intestinal Brush Border Membrane ◽  
High Affinity ◽  
Intestinal Brush Border ◽  
Sodium Gradient

This study utilized intestinal brush-border membrane vesicles obtained from organ donor intestine to characterize the absorption of D-glucose and L-leucine in the human intestine. Both D-glucose and L-leucine were taken up by sodium gradient-dependent active transport along the entire length of the small intestine. The relative magnitude of transport for both substrates under sodium gradient conditions followed the order distal jejunum greater than proximal jejunum greater than distal ileum. The number of carrier systems in these brush-border membrane vesicles was estimated by Eadie-Hofstee plot analysis. This analysis revealed that L-leucine was actively transported via a single high-affinity transport system for the length of the human small intestine. In contrast, the transport of D-glucose occurred via a high-affinity system along the length of the intestine and via a low-affinity, high-flux transport system that was limited to the proximal intestine. Both glucose transport systems were sodium dependent and phlorizin sensitive. The locations and apparent kinetic parameters of these transport systems indicated that these systems function efficiently in vivo as important mechanisms for carbohydrate and protein assimilation in humans. The presence of these active transport systems along the entire small intestine explains the formidable capacity for carbohydrate and protein assimilation in humans.

Effect of pH on Na(+)-dependent phosphate transport in renal outer cortical and outer medullary BBMV

1990 ◽  
Vol 258 (2) ◽  
pp. F356-F363 ◽  
Author(s):  
G. A. Quamme
Keyword(s):  
Brush Border ◽  
Sodium Phosphate ◽  
Membrane Vesicles ◽  
Phosphate Transport ◽  
Transport Systems ◽  
Outer Cortex ◽  
Ph Change ◽  
High Affinity ◽  
Medullary Tissue ◽  
Maximum Uptake Rate

The influence of pH on sodium-phosphate cotransport was determined in brush-border membrane vesicles (BBMV) isolated from outer cortical and outer medullary tissue of porcine kidneys. Two transport systems are apparent in outer cortical brush-border vesicles, and one process is apparent in outer medullary vesicles at all pH values. The apparent maximum uptake rate (Vmax) of the low-affinity system in outer cortex vesicles decreased from 8.3 +/- 1.7 to 3.2 +/- 0.05 nmol.mg protein-1.min-1 with pH change of 8.0 to 6.0, and the high-affinity process changed from 1.3 +/- 0.2 to 0.1 +/- 0.01 nmol.mg protein-1.min-1. The respective affinity values (Km) also decreased 5.5 +/- 0.9 to 0.6 +/- 0.01 mM and 0.08 +/- 0.005 to 0.01 +/- 0.005 mM, respectively, with acidification. In outer medullary vesicles a decrease in pH diminished the apparent Km, 0.28 +/- 0.03 to 0.02 +/- 0.003 mM, and mean Vmax from 3.0 +/- 0.07 to 0.5 +/- 0.1 nmol.mg protein-1.min-1. The mean KNaD values were 22.1 +/- 4.2 mM in outer cortical vesicles (low-affinity system) and 58.7 +/- 7.2 mM in outer medullary vesicles (high-affinity system) and were not altered by pH, suggesting that H+ does not affect the sodium interactive site. The data suggest that the vesicles prepared from outer cortical and outer medullary tissue possess distinctive sodium-phosphate transporters that are sensitive to external H+ concentrations.

Localization of the high-affinity glutamate transporter EAAC1 in rat kidney

1997 ◽  
Vol 273 (6) ◽  
pp. F1023-F1029 ◽  
Author(s):  
Chairat Shayakul ◽  
Yoshikatsu Kanai ◽  
Wen-Sen Lee ◽  
Dennis Brown ◽  
Jeffrey D. Rothstein ◽  
...  
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Rat Kidney ◽  
Cell Volume Regulation ◽  
Glutamate Transporter ◽  
Transport Systems ◽  
Kidney Cortex ◽  
Acid Base Balance ◽  
Western Blots ◽  
High Affinity

Most amino acids filtered by the glomerulus are reabsorbed in the kidney via specialized transport systems. Recently, the cDNA encoding a high-affinity glutamate transporter, EAAC1, has been isolated and shown to be expressed at high levels in the kidney. To determine the potential role of EAAC1 in renal acidic amino acid reabsorption, the distribution of EAAC1 mRNA and protein in rat kidney was examined. In situ hybridization revealed that EAAC1 mRNA is expressed predominantly in S2 and S3 segments of the proximal tubules and at low levels in the inner stripe of outer medulla and inner medulla. Polyclonal antibodies raised against the carboxy terminus of EAAC1 recognized a single band of ∼70 kDa on Western blots of membrane protein from kidney cortex and medulla. Immunofluorescence microscopy revealed intense signals in the luminal membrane of S2 and S3 segments and weaker signals in S1 segments, descending thin limbs of long-loop nephrons, medullary thick ascending limbs, and distal convoluted tubules. These results are consistent with EAAC1 encoding the previously described apical high-affinity glutamate transporter in the kidney that mediates reabsorption of acidic amino acids in tubules beyond early proximal tubule S1 segments. Potential additional roles of EAAC1 in acid/base balance, cell volume regulation, and amino acid metabolism are discussed.

scholarly journals High-affinity potassium and sodium transport systems in plants

2006 ◽  
Vol 57 (5) ◽  
pp. 1149-1160 ◽  
Author(s):  
Alonso Rodríguez-Navarro ◽  
Francisco Rubio
Keyword(s):  
Sodium Transport ◽  
Transport Systems ◽  
High Affinity

scholarly journals Vibrio Iron Transport: Evolutionary Adaptation to Life in Multiple Environments

2015 ◽  
Vol 80 (1) ◽  
pp. 69-90 ◽  
Author(s):  
Shelley M. Payne ◽  
Alexandra R. Mey ◽  
Elizabeth E. Wyckoff
Keyword(s):  
Regulatory Networks ◽  
Iron Transport ◽  
Horizontal Transmission ◽  
Essential Element ◽  
Transport Systems ◽  
Iron Binding ◽  
Content Type ◽  
High Affinity ◽  
Wide Range ◽  
Genes Encoding

SUMMARYIron is an essential element forVibriospp., but the acquisition of iron is complicated by its tendency to form insoluble ferric complexes in nature and its association with high-affinity iron-binding proteins in the host. Vibrios occupy a variety of different niches, and each of these niches presents particular challenges for acquiring sufficient iron.Vibriospecies have evolved a wide array of iron transport systems that allow the bacteria to compete for this essential element in each of its habitats. These systems include the secretion and uptake of high-affinity iron-binding compounds (siderophores) as well as transport systems for iron bound to host complexes. Transporters for ferric and ferrous iron not complexed to siderophores are also common toVibriospecies. Some of the genes encoding these systems show evidence of horizontal transmission, and the ability to acquire and incorporate additional iron transport systems may have allowedVibriospecies to more rapidly adapt to new environmental niches. While too little iron prevents growth of the bacteria, too much can be lethal. The appropriate balance is maintained in vibrios through complex regulatory networks involving transcriptional repressors and activators and small RNAs (sRNAs) that act posttranscriptionally. Examination of the number and variety of iron transport systems found inVibriospp. offers insights into how this group of bacteria has adapted to such a wide range of habitats.

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