The plasma binding protein for vitamin D is a site of discrimination against vitamin D-2 compounds by the chick |
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Authors: | H F DeLuca M Nakada Y Tanaka R Sicinski M Phelps |
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Institution: | Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin-Madison 53706. |
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Abstract: | The binding of 25-hydroxy-26,27-3H]vitamin D-3 and 25-hydroxy-26,27-3H]vitamin D-2 to the vitamin D binding protein in the plasma of both rats and chicks has been studied. In the case of rats, sucrose density gradient analysis, competitive displacement, and Scatchard analysis demonstrate that 25-hydroxyvitamin D-3 and 25-hydroxyvitamin D-2 are bound equally well to the vitamin D binding protein. In contrast, 25-hydroxyvitamin D-2 is poorly bound, while 25-hydroxyvitamin D-3 is tightly bound to the vitamin D binding protein in chick plasma. On the other hand, the chick intestinal receptor binds 1,25-dihydroxyvitamin D-2 and 1,25-dihydroxyvitamin D-3 equally well with a KD of 7.10(-11) M for both compounds. These results strongly suggest that the failure of the plasma transport protein in chicks to bind the vitamin D-2 compounds may be responsible for their relative ineffectiveness in these animals. |
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