Variable region sequence of the light chain from a Waldenstroem's IgM with specificity for phosphorylcholine

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Abstract
The variable region sequence of the L chain from the human IgM [immunoglobulin M] FR with binding activity for phosphorylcholine was determined. Automated Edman degradation was used for the whole chain and for a large cyanogen bromide fragment comprising the 3rd hypervariable region and the entire constant part. The rest of the sequence was established by the Dansyl-Edman technique with tryptic peptides. The sequence of L chain FR can be assigned to the subgroup II of human L chains with which it shares 92% homology within the nonhypervariable (framework) residues. There is no apparent sequence homology between the variable region of the human L chain FR and the amino-terminal 41 residues of the L 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 L chain of the phosphorylcholine binding mouse myeloma protein MOPC 167 indicate a considerable structural homology between the 1st hypervariable region of this murine protein and that of the human IgM FR, suggesting that IgM FR and IgA MOPC 167 were selected by similar antigens.