A New Subgroup of Human L-Chains of the λ-Type.

Bence-Jones protein DEL was isolated from the urine of a patient with multiple myeloma by ammonium sulfate precipitation. Ion-exchange chromatography provided no further purification of the protein; the ammonium sulfate precipitate consisted of only one protein moiety as tested by polyacrylamide electrophoresis. Protein DEL contains 213 amino acids and has a molecular weight of 22500. Eighteen peptides have been isolated by ion-exchange chromatography after tryptic digestion of the completely reduced and aminoethylated protein. Sequence studies were performed mainly on these tryptic peptides. In addition, 14 chymotryptic pepfides were isolated and characterized to obtain overlapping peptides for the whole V-region and for some tryptic peptides of the C-region. Protein DEL is related to subgroups III and IV of the γ-chains as indicated by a deletion of three amino acids after position 27, a common pattern of these two subgroups. Furthermore, position one is deleted in protein DEL as in the other proteins of subgroups IH and IV but in contrast to subgroups I and II of the γ-chains. However, marked differences exist between protein DEL and the proteins of subgroups IH and IV. a) The deletion of two amino acids in positions 95 and 96, characteristic of subgroup IV, was not found in protein DEL. b) 19 of the 27 linked exchanges specific for subgroup IV are substituted in protein DEL. Although the insertion of two amino acids after position 94 is the same as in subgroup III, a high exchange rate was observed for proteins DEL and Sh. Therefore it is concluded that protein DEL does not belong to either subgroups III or IV, but is the first example of a new subgroup of the γ-chains. [ABSTRACT FROM AUTHOR]