Studies on the transport of vitamin D and of 25-hydroxyvitamin D in human plasma.
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.
D000328:Adult; D001692:Biological Transport; D002762:Cholecalciferol / Q000097:blood*; D002848:Chromatography, DEAE-Cellulose; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D006887:Hydroxycholecalciferols / Q000097:blood*; D008297:Male; D013997:Time Factors; D014807:Vitamin D / Q000097:blood*
D006887:Hydroxycholecalciferols; D014807:Vitamin D; D002762:Cholecalciferol