The plasma binding protein for vitamin D is a site of discrimination against vitamin D-2 compounds by the chick.
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.
DeLuca
H F
HF
Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin-Madison 53706.
Nakada
M
M
Tanaka
Y
Y
Sicinski
R
R
Phelps
M
M
D015652:25-Hydroxyvitamin D 2; D000818:Animals; D002112:Calcifediol / Q000097:blood; D002499:Centrifugation, Density Gradient; D002645:Chickens; D004872:Ergocalciferols / Q000031:analogs & derivatives* / Q000097:blood; D008297:Male; D051381:Rats; D013045:Species Specificity; D014809:Vitamin D-Binding Protein / Q000097:blood*
D004872:Ergocalciferols; D014809:Vitamin D-Binding Protein; D015652:25-Hydroxyvitamin D 2; D002112:Calcifediol