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Vitamin D Binding Factors in Bovine Blood¹

Department of Dairy Science, Ohio Agricultural Research and Development Center, Wooster 44691

ABSTRACT

Both 25 [25,26-hydrogen-3] hydroxycholecalciferol and [1,2-hydrogen-3] cholecalciferol were added to bovine plasma in vitro. Analysis by gel-filtration and ion exchange chromatography, electrophoresis, ultracentrifugation, competitive binding specificity studies, and plasma stripping showed that vitamin D circulated with a protein of -globulin mobility. This globulin had a much higher affinity for 25-hydroxycholecalciferol while vitamin D₃ appeared to be associated first with an -lipoprotein and with time became associated with the -globulin. This -globulin had a molecular weight of approximately 70,000 as determined by gel-filtration. Cholecaliciferol appeared to bind tightly to the -lipoprotein and resisted being stripped from the plasma. Thus, -globulin appears to be the major carrier of vitamin D in the blood while the -lipoprotein may aid in the transfer of cholecalciferol from the gut to the liver via the lymph system.

¹ Approved as Journal Article No. 73-76, Ohio Agricultural Research and Development Center, Wooster 44691.

² Data in this paper were presented to the Graduate Faculty of the Ohio State University in partial fulfillment of the requirement for the degree Master of Science (March, 1976).

³ University of Guelph, Department of Nutrition, Guelph, Ontario, Canada.