Chemical Evidence for λ-Type Amyloid Fibril Proteins

A group of proteins comprising the major component of human amyloid fibrils have been shown to have antigenic determinants in common with the amino terminal segment of immunoglobulin light polypeptide chains (1). On the basis of these immunochemical studies amyloid proteins of immunoglobulin origin have been designated as either of λ- or κ-type. Automatic amino acid sequence analysis has demonstrated that the κ-type amyloid fibril proteins are homologous with the amino terminal protion of a κ-Bence Jones (BJ)3 protein (2, 3). Amyloid fibril proteins isolated from four patients have been fractionated by gel filtration to purity as defined by the presence of a single band on sodium dodecyl sulfate polyacrylamide disc gel electrophoresis (4). Immunochemical analysis of these four preparations showed reactions consistent with the presence of λ-light chains (1) and chemical analysis indicated that the polypeptide chains in these preparations had unreactive amino terminal residues (4). In order to determine that the unreactive amino termini were on λ-light chains, we digested the preparations with α-chymotrypsin and recovered and characterized the unreactive amino terminal peptides. The results show that an amino terminal tetrapep-tide identical with that of λ-light chains (5) was present in each case.