Comparative studies on the structure of the light chains of human immunoglobulins. III. Amino acid sequence of a...

Amino acid sequence analysis has been done on a euglobulin-like lambda Bence Jones protein NIG-58 with the major objective of determining the sequence of the variable region. Twenty-seven tryptic peptides with 4 overlapping peptides covering 215 residues, were isolated from completely reduced and aminoethylated protein, and 19 of these were completely sequenced. These comprised the entire variable region and 8 from the constant region. For the remaining peptides covering the rest of constant region, only partial sequences or the amino acid composition were determined. All the tryptic peptides could be arranged in order on the basis of the above results and homology with other lambda chains of known sequences. The sequence of the variable region (residues 0-108) differed from those previously reported in 30 to 50 residues and was classified into the V lambda II subgroup, but no variation was found in the sequence of the last 105 residues. The protein is characteristic of euglobulin and has 2 additional half cystine residues at positions 26 and 28, which forms covalent polymers up to octamer when kept in an alkaline solution.