The genetic variants of group-specific component (vitamin D-binding protein) possess different binding characteristics for immobilized Cibacron Blue 3-GA

The elution profiles of several variants of the Gc protein have been studied after chromatography on immobilized Cibacron Blue 3-GA. The allele products belonging to the Gc1 type were retarded and eluted with a V(e)/V(O) at 1.5, as previously reported for the Gc1-1 phenotype [Chapuis-Cellier, Gianazza & Arnaud (1982) Biochem. Biophys. Acta 709, 353-357]. The allele products belonging to the Gc2 type were further retarded (V(e)/V(O) at 2.6), and both Gc1 and Gc2 allele products were clearly separated in heterozygous individuals. This observation allows the isolation and purification of Gc variants in heterozygous individuals which carry the combination Gc1 variant-Gc2, Gc1-Gc2 variant, or Gc1 variant-Gc2 variant. In contrast, the corresponding holoproteins did not bind to the gel and were eluted in the void volume. This suggests that the interaction of Gc with immobilized Cibacron Blue 3-GA involves the binding site of the protein or 25-hydroxycholecalciferol and that the dye behaves as a 'pseudoligand' for the protein. In addition, our data suggest that the different elution profiles of the variants could reflect a different affinity of the gene products for the dye.