The primary structure of the variable region of an immunoglobin IV light-chain amyloid-fibril protein (AL GIL)

The primary structure of the variable region of an amyloid-fibril protein GIL of immunoglobulin lambda-light-chain origin (AL) was determined. The AL protein obtained from the fibrils in the spleen of a 54-year-old man with primary systemic amyloidosis could be assigned to subgroup IV of the lambda variable-region sequence. About 50% of the protein was found to be truncated in the N-terminus and lacked the first six amino acid residues. The polypeptides consisted of about 146 amino acid residues and contained traces of carbohydrate. An acceptor site for N-glycosylation was found in positions 90-93, but no glycopeptide could be isolated. Comparison of the amino acid sequence of AL protein GIL with that of the only Bence-Jones protein of subgroup IV previously studied revealed a sequence homology of 89%. A similar comparison made with other AL proteins gave sequence homologies below 66%.