scholarly journals The folate-binding protein of rat kidney. Purification, properties, and cellular distribution.

1984 ◽  
Vol 259 (10) ◽  
pp. 6601-6606 ◽  
Author(s):  
J Selhub ◽  
W A Franklin
Keyword(s):  
Binding Protein ◽  
Rat Kidney ◽  
Cellular Distribution ◽  
Folate Binding Protein

Internalization and intracellular transport of folate-binding protein in rat kidney proximal tubule

1993 ◽  
Vol 264 (2) ◽  
pp. C302-C310 ◽  
Author(s):  
H. Birn ◽  
J. Selhub ◽  
E. I. Christensen
Keyword(s):  
Plasma Membrane ◽  
Proximal Tubule ◽  
Brush Border ◽  
Intracellular Transport ◽  
Brush Border Membrane ◽  
Specific Binding ◽  
Binding Protein ◽  
Rat Kidney ◽  
Folate Binding Protein

Folate-binding protein (FBP) is involved in folate reabsorption in the renal proximal tubule. Immunocytochemical studies have located FBP to the brush-border membrane, endocytic vacuoles, and dense apical tubules. We applied the same polyclonal antibody (anti-FBP) against FBP to investigate the dynamic relationship between FBP in the different compartments by microinjecting the antibody into rat kidney proximal tubules in situ. Specific binding of anti-FBP in vivo to the brush-border membrane was followed by fixation at various times. Protein A-gold labeling shows that anti-FBP is transported from endocytic invaginations into vacuoles followed by transport into dense apical tubules within 15 s. Thus FBP is rapidly internalized, and together with previous studies this study strongly suggests recycling of FBP back to the luminal plasma membrane through dense apical tubules. The results are consistent with reabsorption of folate through endocytosis of the FBP-folate complex followed by dissociation and recycling of FBP. When time is allowed there is a steady accumulation of FBP in dense apical tubules combined with an increase in surface density of the same compartment. A possible explanation involves partial inhibition of the fusion between dense apical tubules and plasma membrane because of the anti-FBP labeling of the receptor.

Cell fractionation and electron microscope studies of kidney folate-binding protein

1991 ◽  
Vol 260 (2) ◽  
pp. C338-C346 ◽  
Author(s):  
J. T. Hjelle ◽  
E. I. Christensen ◽  
F. A. Carone ◽  
J. Selhub
Keyword(s):  
Electron Microscope ◽  
Proximal Tubule ◽  
Brush Border ◽  
Binding Protein ◽  
Rat Kidney ◽  
Proximal Tubules ◽  
Cell Fractionation ◽  
Folate Binding Protein ◽  
Em Autoradiography ◽  
Endocytic Vesicles

The subcellular distribution of folate-binding protein (FBP) and [3H]folate in the proximal tubule was examined using cell fractionation and different electron microscope (EM) techniques. Cell fractionation of rabbit proximal tubules revealed that FBP distributed into two modes: 50% of FBP distributed with alanylaminopeptidase activity (brush border), and the remaining FBP distributed with organelles of lower density that did not show a large digitonin-induced shift to greater density. Infusion of [3H]folate into the kidney followed by isolation and fractionation of the proximal tubules revealed a time-dependent shift of [3H]folate from the heavy (brush border) mode to the lighter organelle mode. By EM immunocytochemistry, rat kidney FBP locates in the brush border, endocytic invaginations, endocytic vacuoles, and dense apical tubules of proximal tubule cells. EM autoradiography of rat kidney 10 min after intravenous infusion of [3H]folate revealed that the label was significantly concentrated only in the brush border, endocytic vesicles, and lysosomes. These data support a mechanism of receptor-mediated endocytosis for the process of FBP-mediated folate transport in the kidney.

scholarly journals Evidence for the Presence of Two Active Forms of Cytosolic 3,5,3′-Triiodo-L-thyronine (T3)-binding Protein (CTBP) in Rat Kidney

1989 ◽  
Vol 264 (9) ◽  
pp. 4864-4871
Author(s):  
K Hashizume ◽  
T Miyamoto ◽  
K Ichikawa ◽  
K Yamauchi ◽  
A Sakurai ◽  
...  
Keyword(s):  
Binding Protein ◽  
Rat Kidney

Renal folate absorption and the kidney folate binding protein. II. Microinfusion studies

1987 ◽  
Vol 252 (4) ◽  
pp. F757-F760 ◽  
Author(s):  
J. Selhub ◽  
S. Nakamura ◽  
F. A. Carone
Keyword(s):  
Folic Acid ◽  
Brush Border ◽  
Half Life ◽  
Binding Protein ◽  
Membrane Surface ◽  
Rapid Change ◽  
Acid Uptake ◽  
Folate Binding Protein ◽  
Acid Absorption ◽  
Folic Acid Absorption

Surface proximal convoluted tubules (PCT) in rats were microinfused in situ with [3H]folic acid to study the role of folate binding protein (FBP) in the kidney brush-border membrane for renal conservation and transport of folate [3H]folic acid absorption was linearly related to tubular length of PCT and occurred largely in this segment of the tubule. Unlabeled folate derivatives inhibited [3H]folic acid absorption, the extent of which was dependent on the type of unlabeled folate used and its concentration. At equivalent concentrations, inhibition was most effective with unlabeled folic acid, slightly lower than with 5-methyltetrahydrofolate and least effective with methotrexate. Comparisons between [3H]folic acid absorption before and after infusion of a saturating dose of unlabeled folic acid or repetitive injections of [3H]folic acid into the same tubular site revealed continuous and rapid regeneration of unsaturated folic acid uptake sites with an apparent half-life of 28.75 +/- 8.75 s. Determination of [3H] retained in the tubule at various periods after microinfusion of [3H]folic acid revealed slow cellular disappearance with an apparent half-life of 47.3 +/- 5.4 min. It is proposed that the brush-border FBP functions as a receptor of infused folic acid and that following the binding of the ligand the folic acid/FBP complex undergoes a rapid change that results in the internalization of folic acid and regeneration of unsaturated binding sites at the membrane surface. Internalized folic acid is slowly released into renal capillaries.

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