Renal brush border membrane bound intrinsic factor

The kidney in vitamin B12and folate homeostasis: characterization of receptors for tubular uptake of vitamins and carrier proteins

“…Cubilin purified from kidney binds IF-bound B 12 , and uptake of IF-B 12 in the kidney is inhibited by anti-cubilin antibodies (11). Minute amounts of IF can be detected in human serum and may be filtered, as IF has been identified in urine (111,143). However, due to the very small amounts of B 12 filtered in complex with IF, the significance of cubilin for renal uptake of B 12 is dubious.…”

Glomerular Proteinuria: A Complex Interplay Between Unique Players

“…Several observations refute that this occurs, Maunsbach in the mid-1960’s noted no significant uptake of albumin from the tubular lumen to blood (104). Identification of apical membrane transport proteins like megalin by Kerjaschki and Farquhar (105) followed by cubulin (106–108) provided evidence of expression of proteins in the tubular epithelium which are capable of internalizing albumin, vitamin A, B12 and D. Amsellem et. al reported that cubulin, when conditionally knocked out in tubular epithelial cells resulted in six fold increase in albuminuria compared to basal levels of <30mg/day (109).…”

In Vitro and in Vivo Inactivation of Transcobalamin II Receptor by Its Antiserum

“…Total membrane prepared was suspended and homogenized in 2 ml of (a) 10 mM Tris-HCl buffer, pH 7.5 or (b) 10 mM Tris-HCl adjusted to pH 5 and containing 5 mM EDTA or (c) 0.1 M glycine HCl buffer, pH 3, containing 200 mM KSCN and incubated for 1 h at room temperature. The membranes were pelleted down by centrifugation, washed once with the same respective buffers, re-pelleted down, and finally suspended and homogenized in 10 mM Tris-HCl buffer, pH 7.5, and extracted with Triton X-100 for 6 h. The intrinsic factor-cobalamin receptor activities in the total or in the isolated apical and basolateral membranes were determined using rat IF-[ 57 Co]Cbl (2.5 pmol) as described earlier (16). Protein concentration in membrane and membrane extracts was determined by the method of Bradford (17).…”