Guinea pig immunoglobulin light chain isotypes. I. Separation of kappa and lambda chains and the identification of three isotypes of the lambda chain constant homology region.

The separation of intact kappa chain and two fragments comprising lambda (lambda) chain from immunoglobulin light chain pools isolated from strain 13 guinea pigs is achieved by cyanogen bromide digestion and gel filtration before and after reductive clevage of disulfide bonds. The smaller lambda chain fragment derives from the original carboxyl-terminus of lambda chain. The partial sequence of component tryptic and thermolytic peptides of this thirty-nine residue fragment allowed its complete sequence to be deduced. Three isotypic forms of this lambda chain constant region fragment, distinguished by four residue positions showing alternative amino acids, are found expressed by guinea pigs. Each of these three isotypes is more homologous to the other two than to lambda chains of any other species. The distribution of amino acid substitutions differentiating these isotypes further supports the view that lambda chain isotypes arose in guinea pigs, and in several other species, independently by gene duplication.