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Studies on the mode of action of vitamin D XXXVII 1α-hydroxyvitamin D3: A long-acting 1,25-dihydroxyvitamin D3 analog (1983)

Walters, Marian R. ; Hunziker, Willi ; Bishop, June E. ; [et al.]

Springer

Calcified tissue international 35 (1983), S. 372-375

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ISSN: 1432-0827

Keywords: 1α-Hydroxyvitamin D3 ; Vitamin D3 ; 1,25-Dihydroxyvitamin D3 receptors

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Medicine , Physics

Notes: Summary This study was undertaken to determine whether 1α-hydroxyvitamin D3 [1α(OH)D3] administration to chicks in vivo results in 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] intestinal receptor occupancy and to compare the temporal characteristics of the physiological effects of 1α(OH)D3 and 1,25(OH)2D3 for several days after a single dose of either steroid. Occupied 1,25(OH)2D3 receptors of the chick duodenal mucosa were measured by the recently developed exchange assay procedure [J Biol Chem (1980) 255:9534–9537]. Within 2 h after 1α(OH)D3 injection in rachitic chicks, there was a significant elevation of 1,25(OH)2D3 receptor occupancy in the intestinal mucosa. This observation represents the first direct confirmation that this synthetic analog exerts biological effects through occupancy of 1,25(OH)2D3 receptors. Serum 1,25(OH)2D3 levels reached a 3-fold higher peak after 1,25(OH)2D3 injection (3.25 nmol) than after 1α(OH)D3 injection (6.5 nmol); further, after 1α(OH)D3 injection the peak was delayed by 2–4 h. However, serum 1,25(OH)2D3 levels remained elevated for only 3–6 h after 1,25(OH)2D3, compared to 48 h after 1α(OH)D3 injection. Occupied 1,25(OH)2D3 receptor levels paralleled serum 1,25(OH)2D3 levels at all times after administration of either steroid. At 24 h, duodenal vitamin D-dependent calcium binding protein (CaBP) levels were similarly elevated in both treatment groups, but by 48 and 72 h after 1α(OH)D3 administration CaBP and serum Ca2+, respectively, were more significantly elevated. These data confirm that 1α(OH)D3 induces its major biological effects via intracellular 1,25(OH)2D3 receptors and reinforce the concept that 25-hydroxylation is a prerequisite for these effects. These results also suggest that 1α(OH)D3 may become useful in the therapy for sustained treatment of vitamin D deficiency diseases.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02405061

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Evidence for calcium mediated conformational changes in calbindin-D28K (the vitamin D-induced calcium binding protein) interactions with chick intestinal brush border membrane alkaline phosphatase as studied via photoaffinity labeling techniques (1993)

Leathers, Valerie L. ; Norman, Anthony W.

New York, N.Y. : Wiley-Blackwell

Journal of Cellular Biochemistry 52 (1993), S. 243-252

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ISSN: 0730-2312

Keywords: calbindin ; 1,25(OH)2D3 ; intestinal Ca2+ transport ; alkaline phosphatase ; brush border ; Life and Medical Sciences ; Cell & Developmental Biology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Biology , Chemistry and Pharmacology , Medicine

Notes: The role of the vitamin D-induced calcium binding protein termed calbindin-D (CaBP) in the biological response to 1,25-dihydroxyvitamin D3 was assessed by photoaffinity labeling techniques. The heterobifunctional cross-linking reagent methyl-4-azidobenzoimidate was employed for studies with the 28 KD chick intestinal calbindin-D28K. Calcium-dependent interactions were evident with purified chick intestinal CaBP-immunoglobulins and bovine intestinal alkaline phosphatase; in the absence of Ca2+ there was a greatly diminished crosslinking process. There were also at least two membrane components of chick intestinal brush border membranes, with MR = 60,000 and 130,000, which were photoaffinity cross-linked with CaBP in a calcium-dependent manner. Similar interactions were demonstrated following incubations of CaBP with phosphatidylinositol-specific phospholipase C (PI-PLC)-treated supernatant fractions from chick intestinal brush borders. PI-PLC was shown to release 14% of the alkaline phosphatase from chick intestinal brush borders compared to greater than 80% for rabbit and chick kidney BBM preparations. Specific interactions between CaBP and brush border membrane proteins could also be demonstrated in the absence of photoaffinity labeling by Sephadex G-150 chromatography of Triton X-100 solubilized incubations between calbindin-D28K and chick intestinal BBMS, with 17% of the radiolabelled CaBP comigrating with alkaline phosphatase activity. These studies collectively demonstrate that calbindin-D28K undergoes calcium-dependent conformational changes which alter its subsequent interactions with cellular proteins in a way consistent with other calcium-binding proteins such as calmodulin or troponin C.

Additional Material: 7 Ill.