COMPOSITION AND SUBUNIT STRUCTURE OF INHERITED GROUP-SPECIFIC PROTEIN OF HUMAN SERUM

Amino acid composition, disulfide reduction, peptide maps, and end-group analysis of the group-specific protein (Gc) suggested that this serum protein is comprised of three very similar and indivisible subunits, one of which is common to both fast and slow bands of Gc 1-1 and Gc 2-2. Each of two other subunits seems to be unique to the fast and slow bands, respectively. The presence of three similar but not identical subunits implies three separate genetic loci. Carboxypeptidase digestion of the Gc molecule also demonstrates the presence of isoleucine and leucine in equal quantities suggesting that one-half the subunits have C-terminal leucine and one-half have isoleucine in the C terminus. Faint homology is observed in the C-terminal sequence of serum albumin and Gc. This and previous linkage information indicate the possibility of a common genetic ancestor to the albumin and Gc structural genes. © 1969, American Chemical Society. All rights reserved.