The chick intestinal cytosol binding protein for 1,25-dihydroxyvitamin D3: A study of analog binding |
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Authors: | Barbara E Kream Mimi JL Jose Hector F DeLuca |
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Institution: | Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin-Madison, Madison, Wisconsin 53706 U.S.A. |
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Abstract: | The structural features of 1,25-dihydroxyvitamin D3 that permit its high affinity binding to a 3.7 S protein from chick intestinal cytosol were determined in a series of binding and competition experiments analyzed by sucrose density gradient centrifugation. Optimal binding to the 3.7 S protein was achieved when both 1α- and 25-hydroxyls were present in the vitamin D3 molecule. Modification of the side chain by the introduction of a methyl on C-24 and a double bond on C-22,23 (1,25-dihydroxyvitamin D2) did not alter the binding of 1,25-dihydroxyvitamin D3, but significantly diminished the binding of 25-hydroxyvitamin D3. However, introduction of a hydroxyl on C-24 decreased the ability of either 1,25-dihydroxyvitamin D3 or 25-hydroxyvitamin D3 to compete, especially when the 24-hydroxyl was in the S configuration. These results reveal that the 3.7 S protein requires specific ligand structural features for binding and suggest that metabolite discrimination by the chick intestinal receptor system is likely located in the 3.7 S cytosol protein. |
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Keywords: | To whom all correspondence should be addressed |
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