Journal of Lipid Research, Vol 17, 485-490, Copyright © 1976 by Lipid Research, Inc.
Studies on the transport of vitamin D and of 25-hydroxyvitamin D in human plasma
K Kida and DS Goodman
A study was conducted to investigate whether human plasma contains one or
more than one protein for the transport of vitamin D and of 25-
hydroxyvitamin D (25-OH-D).Serum was labeled in vivo with a mixture of
radioactive vitamin D3 (derived from orally administered tracer vitamin D3)
and of endogenously synthesized labeled 25-OH-D3. Samples of such serum
were subjected to several different protein fractionation procedures. Only
a single peak of protein-bound radioactivity was observed after each of
these procedures. The fraction comprising the ascending and the descending
limbs of the single peak of protein-bound radioactivity (after each
procedure) were separately pooled. In each instance the ratio of
radioactive 25-OH-D3 to radioactive vitamin D3 was found to be almost
identical in both the ascending and the descending limbs. Taken together,
these findings provide strong evidence that human serum contains only a
single binding protein responsible for the normal transport of both vitamin
D and 25-OH-D. Plasma labeled in vitro with added 3H-labeled 25-OH-D3 was
subjected to gel filtration on Sephadex G-200 and to chromatography on
columns of DEAE-cellulose and of SP-Sephadex. After each of these
procedures a single peak of protein-bound radioactivity was observed, with
elution profiles of protein and of radioactivity that were identical with
those observed with in vivo labeled serum. These data indicate that tracer
25- OH-D3 added to plasma in vitro binds to the same plasma protein
normally responsible for the transport of vitamin D and of 25-OH-D.
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