Abstract
High levels of receptor for intrinsic factor-cobalamin (vitamin B12) were detected in human, canine, and rat kidneys. The ratio of specific activity (picomoles/mg of protein) for kidney relative to intestine was 116, 20, and 797, respectively, in these species. The receptor was purified about 3000-fold from 200 g of rat kidney with a recovery of 16% and exhibited a single band on nondenaturing gel electrophoresis. Quantitative amino acid analysis of the receptor gave a value of 457,310 g of amino acid/mol of intrinsic factor-cobalamin binding activity. The pure receptor revealed an Mr of 430,000, as assessed by filtration with Bio-Gel A-5m. Treatment with papain resulted in the production of active monomers of Mr to about 205,000-210,000. Electrophoresis in the presence of sodium dodecyl sulfate confirmed the monomer Mr to be 230,000. The monomer receptor did not reveal the presence of any further subunits upon reductive alkylation. Following cyanogen bromide cleavage the kidney receptor revealed three peptides of Mr 115,000, 60,000, and 54,000. The pI of these peptides was 5.17, 6.17, and 6.17, respectively. Western blot analysis using antiserum raised to the receptor demonstrated a protein with an Mr of 175,000 and 230,000 for intestinal and kidney membrane receptors, respectively. Immunologically, the rat kidney receptor was identical to the rat ileal receptor but was distinct from the canine ileal receptor. Ultrastructural localization revealed the presence of the receptor in the apical surface membrane of proximal tubular cells of the kidney and absorptive cells of the ileum. The kidney is the best source for obtaining this receptor in reasonable quantities.
Highlights
From the Departments of Medicine: Divisions of Gastroenterology, Washington University SchooolfMedicine, St
The receptor was purified about 3000-fold from 200 gof rat kidney with a recovery of 16%and exhibited a single band on nondenaturing gel electrophoresis
Quantitative amino acid analysis of the receptor gave a value of 457,310 g of amino acid/molof intrinsic factor-cobalamin bindingactivity.Thepure receptor revealed an M . of 430,000, as assessed by filtration withBio-Gel A-5m
Summary
Vealed three peptides of M , 115,000, 60,000,and 54,000. The PI of these peptides was 5.17, 6.17, and Materials and Animals. This article must Sepharose as described earlier [8].The receptor was purified as be hereby marked “advertisement” in accordance with 18 follows: 200g of adult rat kidney were homogenizedat full speedin a. The dialyzed material Antiserum to rabbit TC-I1 raised in goat was a gift from Dr Robert was treated with Triton X-100 to give a final concentration of 1%(v/v) and allowed to stir overnight at 4 'C, followed by centrifugation for 1h at 100,000X g. The filters were washed 5 timesfor 15 min with the blocking solution containing 0.05% Nonidet P-40, and incubated for 2h with the blocking solution containing 475 ng of lZ51-proteinA (68 pCi/g of ing the receptor activity (28 nmol of IF-cbl binding ability) CaC12was protein). The receptor antiserum raised to the ratkidney receptor, rat IF, rabbit TC-11, and was stored at 4-5 "C for up to 8 weeks without loss of activity
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