The vitamin D binding of the common and rare variants of the group-specific component (Gc). An autoradiographic study.

The vitamin D3 binding properties of the common and rare Gc variants were examined. Vitamin D3 labeled with 14C was added to serum. Gc phenotypes were demonstrated autoradiographically following separation by immunofixation electrophoresis on agarose. This qualitative analysis did not reveal differences in vitamin D3 binding by the group-specific components of the common types Gc 1-1, Gc 2-1, and Gc 2-2. The double-band variants Gc Darmstadt, Gc Y/Ab, Gc Toulouse, Gc Norway, and Gc Caucasian were examined; the phenotypes Gc Ab-Ab, Gc Ab-1, Gc Ab-1, Gc Ab-2, Gc T-1, Gc T-2, Gc Norw-2, and Gc 1-Cau showed normal D3 binding. The double bands of Gc Darmstadt in the phenotype D-2 appeared somewhat weak. The single-band mutants Gc Wien, Gc Chippewa, Gc Opava, and Gc Z were analyzed; the phenotypes Gc W-1, Gc W-2, Gc Chip-1, Gc Chip-2, Gc 1-Op, Gc Op-2, Gc 1-Z, and Gc 2-Z showed normal D3 binding. A mutant in the Gc system with clearly defective vitamin D3 binding properties remains to be delineated.