Partial primary structure of the immunoglobulin light chain constant region of a single rabbit of b5 allotype

Abstract

The partial amino acid sequence of the constant region of the b5 light chain from the normal IgG of a single rabbit is reported. For structure determination, the IgG light chain was fully reduced and carboxymethylated, then digested with chymotrypsin or trypsin. All chymotryptic peptides covering the constant region from positions 116–210 (117–214 in the standardized numbering system of Kabat et al. ∗ ∗ The numbers in parentheses give the residue number according to the system of Kabat et al. (1979). ) were isolated and purified by column and paper chromatography. Sequences were then determined using traditional sequencing methods. Overlapping was obtained by use of large tryptic peptides, covering positions 138–210 (139–214 ∗ ). The chymotryptic peptide ending with Leu 115(116 ∗ ) could not be obtained in a pure state owing to insolubility and perhaps heterogeneity. When the sequence of this light chain is compared to those of light chains of b4 and b9 allotypes, about 77% homology is found with b4 and 62% with b9. This confirms serological data which would indicate that b4 and b5 allotypes are more similar to each other in structure than they are to b9. The allotypic differences are distributed throughout the whole constant portion of the light chain.