Amino acid sequence analysis of immunoglobulin light chains by gas chromatographic-mass spectrometric techniques: Structural identity of nominal and latent b9 molecules

Light chains with latent allotype b9 were isolated by immunoabsorbent techniques from serum samples taken from a pedigreed rabbit with allotype b⁴b⁴. Amino acid sequence data obtained for the NH₂ terminus of the constant region of these light chains, following acid cleavage of the aspartyl-proline bond at positions 109-110, revealed an NH₂ terminal Sequence characteristic of nominal b9 light chains. The analyses utilized gas chromatography-mass spectrometry to identify dipeptides obtained by digestion of the modified light chains with dipeptidylaminopeptidases I and IV. Similar examinations of b4 light chains revealed significant differences from b9 in the dipeptides obtained. These data provide evidence that light chains bearing latent allotype markers are structurally indistinguishable from those expressed as nominal allotypes.