The group-specific component (Gc), an α2-globulin of human plasma with inherited variations in relative electrophoretic mobility, has been isolated from plasma and partially characterized.
The isolation procedure combines ammonium sulfate fractionation, anion exchange chromatography, preparative zone electrophoresis, and gel filtration. The method is suitable for the isolation and purification of the group-specific components. The Gc proteins representing the gene products of the two common homozygous Gc-types) Gc 1-1 and Gc 2-2, have been prepared. Gc belongs to the group of α2-globulins of relatively low molecular weight (4.1S, molecular weight 50,800) and relatively low carbohydrate content (3.3 per cent). The total amino acid composition of the two homozygous group-specific components is very similar; treatment with reducing agents and alkylation provides no evidence for the presence of more than a single polypeptide chain in the Gc molecule.