Divalent cations and vitamin B12 uptake by intestinal brush-border membrane vesicles

Beesley, Robert C.; Bacheller, C. D.

doi:10.1152/ajpgi.1980.239.6.g452

Cited by 4 publications

(5 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Thus, incubation of ileal cells with IF inactivated by boiling resulted in a 75% inhibition of B12 uptake while incubation in the absence of Ca2+ reduced the level of B12 uptake to that obtained with jejunal cells. Like ileal cells, brush-border membranes derived from ileal enterocytes exhibit IF-and Ca2+ -dependent uptake of B12 (4,11). In the case of isolated brush borders, it has been demonstrated that uptake represents binding of IF-B12 complex to specific receptors localized on these membranes (11).…”

Section: Resultsmentioning

confidence: 99%

Uptake of vitamin B12 by isolated ileal enterocytes.

Beesley

1984

Journal of Nutritional Science and Vitaminology, J Nutr Sci Vit

View full text Add to dashboard Cite

Isolated ileal enterocytes incubated with intrinsic factor-[57Co]vitamin B12 (IF-B12) at 37•Ž took up 25times more B12 than jejunal enterocytes. Uptake of B12 by ileal cells was dependent upon IF and Ca2+. Bit taken up by ileal enterocytes could be separated into two components: 1) B12 which was retained (E component) and 2) released (R-E com ponent) by chelation of divalent cations. The E component could be removed from ileal cells by treatment with Triton X-100. Incubation of ileal enterocytes at 22•Ž or with 2,4-dinitrophenol reduced incorporation of B12 into the E, but not the RE , component. Ileal enterocytes were incubated with IF-[57Co]B12 washed and reincubated with unlabeled IF-B12. Reincubation resulted in a decrease in the amount of [57Co]B12 in the RE component and a concomitant increase of that in the E component indicating that B12 was transferred from the RE to the E component. Dinitrophenol reduced transfer from RE to E components. These results suggest that, using isolated enterocytes, two sequential steps in ileal absorption of B12 can be identified: 1) energy-independent binding of IF-B12 to its receptor on the brush border followed by 2) an energy dependent event which probably represents transfer of B12 from its receptor into the cell.

show abstract

Section: Resultsmentioning

confidence: 99%

Uptake of vitamin B12 by isolated ileal enterocytes.

Beesley

1984

Journal of Nutritional Science and Vitaminology, J Nutr Sci Vit

View full text Add to dashboard Cite

show abstract

“…Intrinsic factor did not compete for these binding sites. The intrinsic-factor-mediated and the milk-binder-mediated mechanisms for vitamin B,, uptake were both present in the 7-and 28-d-old piglets, and were similar in their pH optimum and Ca dependence (Donaldson et al 1967;Mackenzie & Donaldson, 1972;Beesley & Bacheller, 1980), but they appeared to act at different sites in the brush-border membrane.…”

Section: Uptake Of Radioiodinated Vitamin B-binding Protein Influenmentioning

confidence: 90%

“…Ca2+ (as 1 mM-CaC1,) was added to the incubation buffer to optimize intrinsic factormediated uptake of vitamin B,, (Beesley & Bacheller, 1980). Uptake of free vitamin B,, was low and much the same for all three intestinal segments; analysis of variance showed that it was not influenced by the presence of a-lactalbumin or /3-lactoglobulin in the incubation mixture.…”

Section: Uptake Of Vitamin B In the Presence Of Vitamin Biz-binder mentioning

confidence: 99%

“…Brush-border membrane vesicles from intestinal epithelial cells have been much used in studies on intestinal absorption (Beesley & Faust, 1979;Selhub & Rosenberg, 1981 ; Ling & Faust, 1982), and microvillus membrane vesicles prepared from the small intestine of hamsters (Donaldson et al 1967;Mackenzie & Donaldson, 1972;Beesley & Bacheller, 1980) and guinea-pigs (Mathan et al 1974) have been used to examine the influence of intrinsic factor on the uptake of vitamin BIZ. The present investigation was undertaken to complement the experiments in vivo described in a previous paper .…”

mentioning

confidence: 99%

See 1 more Smart Citation

Vitamin B₁₂absorption in the neonatal piglet

Trugo¹,

Ford²,

Salter³

1985

Br J Nutr

View full text Add to dashboard Cite

1. The influence of the vitamin B,,-binding protein isolated from sows' milk on the uptake of vitamin B,, was investigated using microvillus membrane vesicles prepared from the small intestine of 7-and 28-d-old piglets. Uptake of radioiodinated purified binder was also examined.2. The binder strongly promoted uptake of vitamin B,, at both ages; in the absence of the binder there was little uptake. The uptake mechanism was specific and operative in vesicles prepared from all regions of the small intestine. Uptake was a rapid process, exhibiting saturation kinetics, with a pH optimum at about 7.0, and dependent on the presence of magnesium or calcium ions for maximum activity. Atfinity constants of the binding sites for the milk binder were determined.3. Competition experiments using complexes of the binder with vitamin B,, and with non-cobalamin analogues (cobinamide and Co-a-[2-methyladenyl]cobamide) showed that the bound analogues competed with bound vitamin B,, for uptake but with lower efficiency. 4.Intrinsic factor also promoted vitamin B,, uptake by the vesicles but it did not compete with the milk binder for the same binding sites. It promoted uptake only in microvilli isolated from the lower third of the small intestine, and was more effective with preparations from 28-d-old piglets, whereas the milk binder was more effective with the 7-d-old piglets. Porcine gastric cobalophilin competed with the milk cobalophilin, but with lower efficiency.5. It was concluded that a specific transport mechanism for absorption of vitamin B,,, mediated by the vitamin B,,-binder in milk, exists at the intestinal brush border of neonatal piglets and strongly reinforces the developing intrinsic factor-mediated mechanism during the early days or weeks of life.6. It is suggested that the binder in the milk has a wider physiological significance and acts also as a 'host protective' factor and as a scavenger of adventitious vitamin BIZ.

show abstract

“…Binding of the IF-Cbl complex to the IF receptor is energy independent and requires Ca + + and a neutral pH (Levine et al, 1984;Beesley and Bacheller, 1980). Following binding of IF to the IFR, the IFR undergoes an irreversible conformational change .…”

Section: Binding To Ifrmentioning

confidence: 99%