Absence of Intrinsic Factor from Human Portal Plasma during <sup>57</sup>CoB<sub>12</sub> Absorption in Man

Cooper, Bernard A.; White, J. J.

doi:10.1111/j.1365-2141.1968.tb01474.x

Cited by 28 publications

(3 citation statements)

References 10 publications

(9 reference statements)

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“…20 min after uptake 57 Co-B 12 was largely found in endocytic vacuoles and later in lysosomes. The same may be the case in the intestine, where B 12 is known to be transcytosed and secreted basolaterally into blood in complex with TC (35). Studies on polarized human Caco-2 intestinal cells (36) and a renal opossum cell line (37) suggest that proteolysis of IF is a prerequisite for transcytosis of B 12 .…”

Section: Purification Of a ϳ460-kda Protein From Rabbit Renal Cortex mentioning

confidence: 90%

Characterization of an Epithelial ∼460-kDa Protein That Facilitates Endocytosis of Intrinsic Factor-Vitamin B12 and Binds Receptor-associated Protein

Birn

Verroust

Nexø

et al. 1997

Journal of Biological Chemistry

146

128

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(5) to the binding sites is followed by internalization of IF-B 12 and lysosomal degradation of IF, whereas B 12 is transcytosed and secreted to plasma in complex with TC. The receptor, first isolated in small amounts from the ileal mucosa by ligand affinity chromatography, was reported as a 230-kDa protein of unknown structure (8). Later, a protein of a similar size and immunoreactivity was isolated from the kidney cortex (9). Recently, this protein has shown identity (10) with an immunopurified kidney and yolk sac protein, previously referred to as gp280. The latter has been shown previously to be the target of rat teratogenic antibodies (11) and to associate with the endocytic apparatus in rat yolk sac cells (12, 13).The TC-facilitated uptake of B 12 from plasma and various tissue fluids apparently occurs via more than one receptor. One candidate receptor is a 120 -130-kDa membrane protein of unknown structure identified in several human tissues including placenta and liver (14). Another receptor, which we recently identified as a high affinity receptor of TC-B 12 (15), is megalin, the 600-kDa endocytosis-mediating receptor expressed in several absorptive epithelia including renal proximal tubule, yolk sac, and the brain ependyma. The receptor (16 -18) belongs to the low density lipoprotein receptor family and binds, in addition to TC-B 12 , a variety of substances with basic regions, including aminoglycosides (19), clusterin (20), lipoproteins (21), and RAP (21-23). The last represents a 40-kDa endoplasmic reticulum protein serving as a novel kind of chaperone or escort protein preventing aggregation of RAP-binding receptors (24,25). RAP affinity chromatography represents an effective way of purifying megalin (26,27).In the present study we have identified and characterized the function of a high molecular mass protein (ϳ460 kDa) eluting together with megalin from a RAP-Sepharose column loaded with solubilized renal cortical membranes. Surprisingly, we observed that whereas megalin binds TC-B 12 but not IF-B 12 , the copurifying ϳ460-kDa protein displays a high affinity for IF-B 12 but not for TC-B 12 . Extended analyses of the molecular ligand-receptor interaction and the in vivo uptake in

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Section: Purification Of a ϳ460-kda Protein From Rabbit Renal Cortex mentioning

confidence: 90%

Characterization of an Epithelial ∼460-kDa Protein That Facilitates Endocytosis of Intrinsic Factor-Vitamin B12 and Binds Receptor-associated Protein

Birn

Verroust

Nexø

et al. 1997

Journal of Biological Chemistry

146

128

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“…Using the technique of immune electron microscopy Levine et al (105) concluded that IF is not internalized during absorption. Supporting this concept is the observation of Cooper & White (35), who failed demonstrate IF in the portal circulation. On the other hand, Kapadia et al (97) have shown that labelled rabbit IF does penetrate the enterocytes and is present in the cytosol.…”

Section: Mucosal Phasementioning

confidence: 90%

Absorption and Transport of Cobalamin (Vitamin B₁₂)

Seetharam

Alpers

1982

Annu. Rev. Nutr.

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This review apprises the reader of recent advances in cobalamin absorption and transport since 1970. This field has been of interest to gastroenterologists, hematologists, and biochemists as well as nutritionists. Clinical conditions leading to cobalamin deficiency present especially to the first two of these specialties. Many recent advances involve biochemical definition of the specific transport proteins themselves. Full understanding of the multiple clinical conditions associated with cobalamin deficiency requires some knowledge of these proteins. We do not discuss every paper in the field, especially the early literature (see 47, 61, 150). Despite rapid strides in understanding the mechanism of absorption and transport of cobalamin both in prokaryotic and eukaryotic cells, the complete sequence of events during cellular absorption at the plasma membrane level and events in the cells that mediate intracellular movement of cobalamin have not been elucidated completely. Here we emphasize the current state of knowledge about cobalamin absorption and transport in man and other mammalian systems, particularly the physiological role and biochemical nature of proteins involved (intrinsic factor, intrinsic factor-cobalamin receptor, transcobalamins).

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“…Intrinsic factor (IF), the transport glycoprotein of the intestine, does not pass through into the portal blood but gives up its vitamin B,, to the plasma transport system (Cooper and White, 1968). The absorbed vitamin B,, is taken up by TC 11, which is the main binder of vitamin B,, added to or injected into plasma.…”

Section: The First Stage Ofplasma Transport Of Vitnmiti Bmentioning

confidence: 99%

TRANSPORT OF VITAMIN B₁₂ IN MAN

Hall¹

1969

Br J Haematol

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Absence of Intrinsic Factor from Human Portal Plasma during ⁵⁷CoB₁₂ Absorption in Man

Cited by 28 publications

References 10 publications

Characterization of an Epithelial ∼460-kDa Protein That Facilitates Endocytosis of Intrinsic Factor-Vitamin B12 and Binds Receptor-associated Protein

Characterization of an Epithelial ∼460-kDa Protein That Facilitates Endocytosis of Intrinsic Factor-Vitamin B12 and Binds Receptor-associated Protein

Absorption and Transport of Cobalamin (Vitamin B₁₂)

TRANSPORT OF VITAMIN B₁₂ IN MAN

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Absence of Intrinsic Factor from Human Portal Plasma during 57CoB12 Absorption in Man

Cited by 28 publications

References 10 publications

Characterization of an Epithelial ∼460-kDa Protein That Facilitates Endocytosis of Intrinsic Factor-Vitamin B12 and Binds Receptor-associated Protein

Characterization of an Epithelial ∼460-kDa Protein That Facilitates Endocytosis of Intrinsic Factor-Vitamin B12 and Binds Receptor-associated Protein

Absorption and Transport of Cobalamin (Vitamin B12)

TRANSPORT OF VITAMIN B12 IN MAN

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Product

Resources

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Absence of Intrinsic Factor from Human Portal Plasma during ⁵⁷CoB₁₂ Absorption in Man

Absorption and Transport of Cobalamin (Vitamin B₁₂)

TRANSPORT OF VITAMIN B₁₂ IN MAN