Purification of vitamin D binding proteins (group-specific components) in human plasma using a chromatofocusing method.

Abstract

Human plasma vitamin D binding proteins (DBP, also denoted as group-specific components ; Gc) were highly purified from commercial human α-globulin (also denoted as Cohn Fraction IV ; HαG). Chromatofocusing separated the partially purified HαG into three DBPs which had the same molecular size in gel permeation high-performance liquid chromatography. They each exhibited binding affinity with 25-hydroxyvitamin D3 [25 (OH) D3] and cross-immunoreactivity against antihuman plasma group-specific components (Gc) antiserum. However, the three DBPs were completely different in charge on chromatofocusing, and gave distinct peaks having apparent isoelectric points of 4.64, 4.59 and 4.54. It is well known that the Gc has three phenotypes separable only by isoelectric focusing. The relationship between the three purified DBPs and the three phenotypes of Gc has not been clarified. However, we suggest that the chromatofocusing method may provide a convenient procedure for the purification of DBP from human plasma and commercial HαG.