scholarly journals The response of the small intestine to vitamin D. Correlation between calcium-binding-protein production and increased calcium absorption

1974 ◽  
Vol 144 (2) ◽  
pp. 339-346 ◽  
Author(s):  
J S Emtage ◽  
D E M Lawson ◽  
E Kodicek
Keyword(s):  
Vitamin D ◽  
Protein Synthesis ◽  
Small Intestine ◽  
Calcium Binding ◽  
Protein Production ◽  
Calcium Absorption ◽  
Binding Protein ◽  
Calcium Binding Protein ◽  
Intestinal Cell ◽  
Stimulation Of

1. The synthesis of calcium-binding protein, a protein produced in the small intestine in response to vitamin D, was investigated with a view to determining whether calcium-binding-protein production could be correlated with the stimulation of calcium absorption by vitamin D. 2. A radioimmunological assay, which can quantitatively estimate calcium-binding-protein concentrations as low as 1μg/g wet wt., was used to detect the synthesis of soluble calcium-binding protein. 3. When used on intestinal supernatants from chicks dosed with vitamin D, calcium-binding protein was not detectable at 8h but was present after 12h at a concentration of 8.6μg/g wet wt.; in agreement with this an increase in calcium absorption due to vitamin D was detected at 12h but not at 8h. 4. The synthesis of calcium-binding protein was also monitored directly by making use of the ability of the iodinated antiserum to bind specifically to nascent calcium-binding protein chains on intestinal polyribosomes; in this way calcium-binding-protein synthesis could be detected 8h after dosage with vitamin D. Further, the binding reaction indicated a near linear increase in the calcium-binding-protein-synthesizing capacity over a 16h period. 5. From the amount of calcium-binding protein present 12 and 24h after vitamin D administration it is calculated that calcium-binding-protein mRNA is produced at approx. 1mol/min per intestinal cell. 6. It is concluded that the high correlation between the initiation of calcium-binding-protein synthesis and the stimulation of calcium absorption by vitamin D strengthens the proposal that calcium-binding protein plays an important role in calcium transport.

scholarly journals The response of the small intestine to vitamin D. Isolation and properties of chick intestinal polyribosomes

1974 ◽  
Vol 140 (2) ◽  
pp. 239-247 ◽  
Author(s):  
J. Spencer Emtage ◽  
D. Eric M. Lawson ◽  
Egon Kodicek
Keyword(s):  
Vitamin D ◽  
Small Intestine ◽  
Rat Liver ◽  
Liver Cell ◽  
Calcium Binding ◽  
De Novo ◽  
Binding Protein ◽  
Calcium Binding Protein ◽  
Intestinal Cell ◽  
Polypeptide Chains

Undegraded polyribosome preparations may be obtained from chick intestinal mucosa if ribonuclease activity is strictly controlled. This is best achieved by homogenization of the mucosa directly in rat liver cell-sap. 2. The extent of amino acid incorporation by chick intestinal polyribosomes is greatly influenced by the source of the cell-sap. Sephadex-treated intestinal cell-sap caused impaired incorporation and release of completed polypeptide chains, whereas Sephadex-treated rat liver cell-sap promoted the polymerization of up to 90 amino acids per ribosome. Under optimum conditions 30–35% of the nascent polypeptide chains are completed and released. 3. The preparation of an antiserum against the calcium-binding protein formed in response to vitamin D is described. It is shown that the antiserum is highly specific for calcium-binding protein. 4. This antiserum was used to investigate the ability of chick intestinal polyribosomes to synthesize calciumbinding protein. Only polyribosomes from chicks receiving vitamin D have the ability to synthesize calcium-binding protein. Moreover, the product formed in vitro has the same electrophoretic mobility as calcium-binding protein synthesized in vivo. 5. It is concluded that one of the main functions of vitamin D in the small intestine is to induce the synthesis de novo of calcium-binding protein.

scholarly journals The relationship between vitamin D-stimulated calcium transport and intestinal calcium-binding protein in the chicken

1978 ◽  
Vol 170 (1) ◽  
pp. 93-101 ◽  
Author(s):  
Rosemary Spencer ◽  
Marilyn Charman ◽  
Peter W. Wilson ◽  
D. Eric M. Lawson
Keyword(s):  
Vitamin D ◽  
Protein Synthesis ◽  
Calcium Binding ◽  
Binding Protein ◽  
Protein Biosynthesis ◽  
Calcium Content ◽  
Calcium Binding Protein ◽  
Intracellular Protein ◽  
Maximum Increase ◽  
Stimulation Of

1. The rapid stimulation of intestinal Ca2+transport observed in vitamin D-deficient chicks after receiving 1,25-dihydroxycholecalciferol has necessitated a re-evaluation of the correlation hitherto observed between this stimulation and the induction of calcium-binding protein synthesis. By 1h after a dose of 125ng of 1,25-dihydroxycholecalciferol, Ca2+transport is increased. This is at least 2h before calcium-binding protein can be detected immunologically and 1h before synthesis of the protein begins on polyribosomes, and thus the hormone stimulates Ca2+transport before calcium-binding-protein biosynthesis is induced. 2. The maximum increase in Ca2+transport observed after this dose of 1,25-dihydroxycholecalciferol (attained by 8h) is similar to that observed after 1.25–25μg of cholecalciferol, but the stimulation is only short-lived, in contrast with the effect observed after the vitamin. At later times after the hormone, however, when Ca2+transport has declined to its basal rate, the cellular content of calcium-binding protein remains elevated. 3. Calcium-binding protein is synthesized on free rather than membrane-bound polyribosomes, which implies that it is an intracellular protein. 4. Rachitic chicks require the presence of dietary calcium for maximum stimulation of calcium-binding protein production by cholecalciferol. 5. These results suggest that calcium-binding protein is an intracellular protein, and that its synthesis may be a consequence of the raised intracellular calcium content of the intestinal epithelial cells resulting from 1,25-dihydroxycholecalciferol-stimulated Ca2+transport. We propose that calcium-binding-protein synthesis is necessary for maintaining the stimulated rate of Ca2+transport, which is initiated by other factors.

Calcium absorption and intestinal calcium-binding protein: quantitative relationship.

1979 ◽  
Vol 236 (5) ◽  
pp. E556 ◽  
Author(s):  
J J Feher ◽  
R H Wasserman
Keyword(s):  
Vitamin D ◽  
Vitamin D3 ◽  
Calcium Binding ◽  
Calcium Absorption ◽  
Binding Protein ◽  
Quantitative Relationship ◽  
Calcium Binding Protein ◽  
Vitamin D Status ◽  
Loop Technique

The concentration of the vitamin D-induced calcium-binding protein (CaBP) and calcium absorption from the duodenum were investigated in chicks with an in vivo ligated-loop technique. The relation between CaBP and calcium absorption was dependent on a) source of vitamin D activity (either vitamin D3 or 1,25-dihydroxycholecalciferol); b) dosage of vitamin D3; c) time after administration of vitamin D3 to rachitic animals. To aid in the interpretation of these results, a phenomenological model was developed in which CaBP was viewed as being linearly related to a portion of calcium absorption. The model, when applied to the data, suggests that there is a "nonfunctional" pool of CaBP the size of which is determined by the vitamin D status of the animal. After correction for this nonfunctional pool, the proportionality between CaBP and calcium absorption is independent of the vitamin D status of the animal.

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