Research for the primary structures of human vitamin D-binding proteins.

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Gc protein is one of human serum protein, which is widely available in the field of legal medicine and human genetics, and has several phenotypes controlled by three codominat genes (Gc2, Gc1F, and Gc1S) on isoelctric focusing electrophoresis. This protein, which is called vitamin D-binding protein (DBP) by the character, has important functions under the affinity of actin in serum or on lymphocyte. The primary structure of DBP, which many researchers in the world could not clarify in spite of many approaches, was determined through the base sequence analyses of that cDNA by Yang on 1985. We intended to confirm this amino acid sequence speculated by the base sequence and to elucidate the amino acid substitutions between Gc subtypes. DBPs were purified from human sera by salting and chromatography. The BrCN peptides of carboxymethylated DBP were separated by hiph-performance liquid chromatography, and further purification of the enzymatic digests of BrCN peptide was carried out on reversed-phase chromatography. We confirmed the primary structure of DBP (Gc2) by the amino acid composition analyses and the amino acid sequence analyses of these peptides. The sequence analysis of DBP carrying Gc1F or 1S was done by the same procedures. From these results, the amino acid substitutions between DBP subtypes are GLY-GLU-GlU (Gc2-1F-1S) at position 152, ASP-ASP-GLU at position 416, and LYS-THR-THR at position 420.