Fragments of the constant region of immunoglobulin light chains are constituents of AL-amyloid proteins.

Immunoglobulin light chains are the precursor proteins of AL-amyloidosis. In the fibril formation process properties of the variable part of the immunoglobulin light chains are believed to be of major importance. In this work it is shown that fragments of the constant part of the immunoglobulin light chain are a constituent of the AL-amyloid proteins of kappa type. A specific antiserum has identified these fragments in gel filtration fractions where the absorbance approached the base line after the main retarded peak. The fragments are small and have been overlooked previously in the purification process. The significance of the constant part in AL-proteins is unclear, but adds new aspects to the discussion of pre- or post-fibrillogenic cleavage of the immunoglobulin light chains.