Variable region sequence of the light chain from a Waldenströms IgM with specificity for phosphorylcholine

The variable region sequence of the light chain from the human IgM FR with binding activity for phosphorylcholine has been determined. Automated Edman degradation was used for the whole chain and for a large cyanogen bromide fragment comprising the third hypervariable region and the entire constant part. The rest of the sequence was established by means of the "Dansyl-Edman" technique with tryptic peptides. The sequence of light chain FR can be assigned to the subgroup II of human light chains with which it shares 92% homology within the nonhypervariable (frame-work) residues. There is no apparent sequence homology betweeen the variable region of the human light chain FR and the aminoterminal 41 residues of the light chains published so far from the mouse myeloma proteins TEPC 15, HOPC 8, S 107, and McPC 603 with phosphorylcholine binding activity. Recent data on the light chain of the phosphorylcholin binding mouse myeloma protein MOPC 167 (see Conclusion), however, indicate a considerable structural homology between the first hypervariable region of this murine protein and that of the human IgM FR, suggesting that both IgM FR and IgA MOPC 167 might have been selected by similar antigens.