The Amino Acid Sequence of a λ Type Bence-Jones Protein: I. TRYPTIC PEPTIDES

Abstract

Abstract Amino acid sequence analysis has led to the concept that the NH2-terminal portion of Bence-Jones proteins is subject to variation in sequence whereas the COOH-terminal portion is invariant, yet the proof of sequence has in no case been reported. For determination of the sequence of the soluble tryptic peptides, the human κ Bence-Jones protein Ag, which has served as the standard for comparison, was reduced and carboxymethylated, and digested with trypsin. The soluble peptides were purified by column chromatography, paper chromatography, and paper electrophoresis. The amino end groups and the composition of the intact protein and the tryptic peptides were determined. The amino acid sequences of 16 soluble tryptic peptides were determined by standard procedures, principally by use of the Edman degradation and further enzymatic cleavage. The sequences of the 16 tryptic peptides account for 140 residues and are in accord with the tentative sequence reported earlier for Protein Ag. Eleven of the peptides are derived from the constant portion of the human κ light chain which has a uniform sequence except for a genetic variation at 1 residue. The remaining peptides are from the variable portion of the κ chain and differ in many respects from corresponding portions of the provisional sequences of other human κ chains.