The Primary Structure of a Monoclonal Human λ‐Type Immunoglobulin L‐Chain of Subgroup II (Bence‐Jones Protein NEI)

Protein NEI, which has a molecular weight of 23 500 and contains 216 amino acids, was isolated from the urine of a patient with multiple myeloma by salt‐precipitation and purified by ion‐exchange chromatography, block electrophoresis and gel filtration. 23 tryptic peptides have been isolated from the aminoethylated protein and 13 chymotryptic peptides from the carboxymethylated protein by ion‐exchange chromatography. Sequence studies have mainly been carried out with the tryptic peptides; the chymotryptic peptides have been used for overlaps in the variable region, since the alignment of the tryptic peptides by homology was not unambiguous. Protein NEI belongs to subgroup II of the λ‐chains. It has a series of subgroup specific exchanges and a subgroup specific deletion at position 96. Protein NEI differs from all other λ‐chains of subgroup II by possessing a sixth cysteine residue. This additional cysteine residue at position 88 is so far unique, as it is adjacent to an invariant cysteine at position 87. Protein NEI also contains a carbohydrate moiety attached to an aspartic acid or asparagine (Asx) residue at position 93, one of the hypermutable areas of the variable part. Furthermore we conclude by comparison with other λ‐chains that all completely elucidated λ‐chains can be ordered into four subgroups. The subgroups and linkage groups within subgroups are in complete agreement with an evolutionary origin of antibody variability and are incompatible with somatic hypermutation models.