Comparative studies on monotypic IgMlamba and IgGkappa from an individual patient. II. Amino-terminal sequence...

Amino terminal sequence analyses were performed on the H and L chains of the idiotypically related IgMlambda and IgGkappa paraproteins isolated from the sera of a patient, Br. The N-terminal 41 residues of the Br k-chain belonged to the Vkiii subgroup, and L chains derived from BrIgMlambda revealed a blocked N-terminus characteristics of lambda-chains. Comparative sequence analysis of the Br mu- and gamma-chains indicated that, although both possessed an unblocked N-terminal glutamic acid, the respective VH regions belonged to seperate subgroups. The N-terminal 27 residues of the Br mu-chain reflected a typical VHiii subgroup sequence. The Br gamma-chain sequence demonstrated a VHI pattern with an unblocked N-terminus. These structural data stand in contrast to previously reported serologic evidence, which indicated that the BrIgMlambda and BrIgGkappa proteins possessed highly similar Vh-associated idiotypic determinants. Final interpretation of these findings of similar Vh idiotypic determinants expressed by H chains belonging to seperate Vh subgroups must await complete sequence analysis of hypervariable segments of the Br gamma- and mu-chains.