scholarly journals Involvement of disulphide bonds in the renal sodium/phosphate co-transporter NaPi-2

1997 ◽  
Vol 323 (2) ◽  
pp. 401-408 ◽  
Author(s):  
Yansen XIAO ◽  
Christian J.-C. BOYER ◽  
Éric VINCENT ◽  
André DUGRÉ ◽  
Vincent VACHON ◽  
...  
Keyword(s):  
Sodium Phosphate ◽  
Polyclonal Antibodies ◽  
Membrane Vesicles ◽  
Phosphate Transport ◽  
Reducing Agents ◽  
Western Blots ◽  
Disulphide Bonds ◽  
Reducing Conditions ◽  
Renal Brush Border Membrane ◽  
Radiation Induced

The rat renal brush border membrane sodium/phosphate co-transporter NaPi-2 was analysed in Western blots with polyclonal antibodies raised against its N-terminal and C-terminal segments. Under reducing conditions, proteins of 45–49 and 70–90 kDa (p45 and p70) were detected with N-terminal antibodies, and proteins of 40 and 70–90 kDa (p40 and p70) were detected with C-terminal antibodies. p40 and p45 apparently result from a post-translational cleavage of NaPi-2 but remain linked through one or more disulphide bonds. Glycosidase digestion showed that both polypeptides are glycosylated; the cleavage site could thus be located between Asn-298 and Asn-328, which have been shown to constitute the only two N-glycosylated residues in NaPi-2. In the absence of reducing agents, both N-terminal and C-terminal antibodies detected p70 and a protein of 180 kDa (p180), suggesting the presence of p70 dimers. Much higher concentrations of β-mercaptoethanol were required to produce a given effect in intact membrane vesicles than in solubilized proteins, indicating that the affected disulphide bonds are not exposed at the surface of the co-transporter. Phosphate transport activity decreased with increasing concentrations of reducing agents [β-mercaptoethanol, dithiothreitol and tris-(2-carboxyethyl)phosphine] and was linearly correlated with the amount of p180 detected. The target sizes estimated from the radiation-induced loss of intensity of p40, p70 and p180 were all approx. 190 kDa, suggesting that NaPi-2 exists as an oligomeric protein in which the subunits are sufficiently close to one another to allow substantial energy transfer between the monomers. When protein samples were pretreated with β-mercaptoethanol [2.5% and 5% (v/v) to optimize the detection of p40 and p70] before irradiation, target sizes estimated from the radiation-induced loss of intensity of p40 and p70 were 74 and 92 kDa respectively, showing the presence of disulphide bridges in the molecular structure of NaPi-2.

Characterization of the rabbit renal Na(+)-dicarboxylate cotransporter using antifusion protein antibodies

1996 ◽  
Vol 271 (6) ◽  
pp. C1808-C1816 ◽  
Author(s):  
A. M. Pajor ◽  
N. Sun
Keyword(s):  
Fusion Protein ◽  
Brush Border ◽  
Xenopus Oocytes ◽  
Polyclonal Antibodies ◽  
Membrane Vesicles ◽  
Site Directed Mutagenesis ◽  
In Vitro Translation ◽  
Western Blots ◽  
Renal Brush Border Membrane

Polyclonal antibodies were prepared against the rabbit renal Na(+)-dicarboxylate cotransporter, NaDC-1. The antibodies were raised in chickens against a fusion protein consisting of a 60-amino acid peptide from NaDC-1 and glutathione S-transferase. These antibodies specifically recognized the fusion protein in Western blots and could immunoprecipitate the full-length NaDC-1 after in vitro translation. The antifusion protein antibodies specifically recognized a protein of 63 kDa in rabbit renal brush-border membrane vesicles (BBMV), similar to the predicted mass of 66 kDa. Two proteins of 57 and 115 kDa were recognized in rabbit intestinal brush-border membranes. A protein of 66 kDa was recognized in Xenopus oocytes injected with NaDC-1 cRNA. Enzymatic deglycosylation of rabbit renal BBMV resulted in a decrease in mass by 11 kDa, consistent with N-glycosylation at a single site. Site-directed mutagenesis of the two consensus sequences for N-glycosylation in the NaDC-1 cDNA showed that Asn-576, located near the COOH-terminal, is glycosylated. The nonglycosylated mutant of NaDC-1 exhibited 50% of wild-type succinate transport activity when expressed in Xenopus oocytes, suggesting that glycosylation is not essential for function. The revised secondary structure model of NaDC-1 contains 11 putative transmembrane domains and an extracellular glycosylated COOH-terminal.

Effect of temperature and pH on phosphate transport through brush border membrane vesicles in rats

1984 ◽  
Vol 62 (2) ◽  
pp. 229-234 ◽  
Author(s):  
Michèle G. Brunette ◽  
Richard Beliveau ◽  
Meanthan Chan
Keyword(s):  
Brush Border ◽  
Brush Border Membrane ◽  
Phosphate Uptake ◽  
Membrane Vesicles ◽  
Phosphate Transport ◽  
Mean Value ◽  
Brush Border Membrane Vesicles ◽  
Effect Of Temperature ◽  
Total Phosphate ◽  
Renal Brush Border Membrane

The kinetics of sodium gradient dependent phosphate uptake by the renal brush border membrane vesicles of the rat have been studied under various conditions of temperature and pH. From 7 to 30 °C the Lineweaver-Burk plots are linear, and the apparent Km progressively increases from 54 to 91 μM. Above 30 °C, the apparent Km continues to increase to reach 135 μM at 40 °C, but a break is observed in the Lineweaver-Burk plots at the substrate concentration of 300 μM. The existence of this break, confirmed by the Eadie-Hofstee plot supports the hypothesis of a dual mechanism of phosphate transport, one for low concentrations of substrate with a Km of 100 μM and the other for high concentrations with a Km of approximately 240 μM. When the two components of the Eadie-Hofstee plot are analyzed according to a nonlinear regression program, these two values of Km become 70 μM and 1.18 mM, respectively. The Vmax continuously increases with temperature. However, the Arrhenius plot (In Vmax vs. 1/Tk) shows an abrupt discontinuity at 23 °C. pH experiments were performed at 35 °C. In the absence of a proton gradient, increasing the pH from 6.5 to 7.5 and 8.5 decreases the apparent Km from 341 to 167 and 94 μM, respectively. When only the divalent form of phosphate is considered as the substrate, the apparent Km does not vary anymore with the pH and remains around the mean value of 105 μM. The uniformity of the apparent Km for the total phosphate uptake, when only the divalent phosphate is considered as being the substrate, suggests that this divalent form is the only one which is transported. Whatever the substrate considered, total phosphate or divalent phosphate, the highest Vmax is obtained at pH 7.5 which probably approximates the optimum pH inside the vesicles for the phosphate uptake.

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.

scholarly journals Effects of insulin and glucose on renal phosphate reabsorption: interactions with dietary phosphate.

1992 ◽  
Vol 2 (11) ◽  
pp. 1593-1600
Author(s):  
M Allon
Keyword(s):  
Phosphate Uptake ◽  
Membrane Vesicles ◽  
Phosphate Transport ◽  
Tubular Reabsorption ◽  
Insulin Deficiency ◽  
Renal Brush Border Membrane ◽  
Renal Phosphate Reabsorption ◽  
Catabolic State ◽  
Dietary Phosphate ◽  
Phosphate Depletion

Both insulin deficiency and glycosuria are known to inhibit the tubular reabsorption of phosphate. This inhibition has previously been evaluated either in the fasted state or on a normal phosphate diet. The goal of this study was to evaluate how dietary phosphate depletion affected the relative effects of insulin deficiency and glycosuria on the tubular reabsorption of phosphate. Rats were maintained on either a low- (0.03%) or normal (0.8%) phosphate diet. After 5 days, one half of the animals in each group received streptozotocin to induce short-term insulin deficiency, whereas the other half received vehicle alone. Two days later, sodium-dependent phosphate uptake by renal brush border membrane vesicles (BBMV) was evaluated in each of the four experimental groups. The effect of glucose on phosphate uptake was determined by the addition of varying concentrations of glucose (between 0 and 32 mmol/L) to the extravesicular transport fluid. BBMV phosphate uptake was about threefold higher in the nondiabetic rats fed a low-phosphate diet as compared with the nondiabetic animals maintained on a normal phosphate diet. In rats maintained on a low-phosphate diet, streptozotocin treatment prevented the increase in BBMV phosphate transport; in contrast, in animals fed a normal phosphate diet, streptozotocin treatment had no effect on BBMV phosphate transport. Extravesicular glucose significantly inhibited phosphate transport in a dose-related manner, regardless of dietary phosphate or insulin status. Because fasting mimics the catabolic state associated with insulin deficiency, BBMV phosphate transport was also measured in rats fasted for 48 h after the administration of streptozotocin or vehicle.(ABSTRACT TRUNCATED AT 250 WORDS)

Sulfate inhibits [14C]phosphonoformic acid binding to renal brush-border membranes

1990 ◽  
Vol 259 (2) ◽  
pp. F286-F292 ◽  
Author(s):  
H. S. Tenenhouse ◽  
J. Lee
Keyword(s):  
Brush Border ◽  
Ph Dependence ◽  
Membrane Vesicles ◽  
Phosphate Transport ◽  
Sulfate Transport ◽  
Phosphonoformic Acid ◽  
Renal Brush Border Membrane ◽  
Renal Brush Border Membranes ◽  
Decreasing Ph ◽  
Renal Brush Border

To examine the specificity of the phosphonoformic acid (PFA) interaction with the Na(+)-dependent phosphate transporter of mouse renal brush-border membrane vesicles, we compared the effects of anions on Na(+)-dependent [14C]PFA binding and Na(+)-dependent phosphate transport. Inhibition of PFA binding was achieved by PFA (% control = 0 +/- 1), sulfate (15 +/- 2), arsenate (35 +/- 1), phosphate (59 +/- 2), and nitrate (68 +/- 4), whereas inhibition of phosphate transport was only apparent with phosphate (0 +/- 1), PFA (22 +/- 4), and arsenate (37 +/- 5). Succinate and gluconate had no effect on either Na(+)-dependent process. Under conditions where Na(+)-dependent PFA binding was maximally inhibited by phosphate (% control = 65 +/- 4), further inhibition could be achieved by sulfate (26 +/- 5%). Na(+)-dependent PFA binding was competitively inhibited by phosphate (apparent Ki = 8.9 +/- 1.2 mM) and noncompetitively inhibited by sulfate (apparent Ki = 2.6 +/- 0.5 mM). We found that PFA inhibited Na(+)-dependent sulfate transport (50% inhibition at 9 mM PFA) as well as Na(+)-dependent phosphate transport (50% inhibition at 0.5 mM PFA). We also examined the pH dependence of Na(+)-dependent PFA binding and Na(+)-dependent phosphate and sulfate transport. PFA binding was optimal at pH = 7.4, whereas phosphate transport increased with increasing pH, and sulfate transport increased with decreasing pH.(ABSTRACT TRUNCATED AT 250 WORDS)

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