SYSTEMIC IMMUNOGLOBULIN (AL) AMYLOIDOSIS IN A CAT - COMPLETE PRIMARY STRUCTURE OF A FELINE LAMBDA-LIGHT CHAIN

A tarsal mass removed from a ten year old cat proved to be an extramed ullary plasmacytoma largely composed of amyloid. Systemic amyloidosis was indicated when histological examination at necropsy identified amy loid also in the lymph nodes, spleen and liver. The amyloid subunit pr otein was isolated by molecular sieve chromatography of reduced and al kylated fibrils extracted from the mass, and its amino acid sequence w as determined by sequence analysis of peptides isolated after digestio n with trypsin or Stapylococcus protease. The sequence of the C-termin al half of the protein was homologous to the constant region of immuno globulin lambda light chains of other species establishing the immunog lobulin origin of the amyloid. The N-terminal half of the protein was homologous to the variable region of human lambda light chains and con tained several rare residues in the framework regions. To our knowledg e, this is the first complete sequence determination of a feline immun oglobulin light chain, and the first complete sequence determination o f an amyloid immunoglobulin light chain from a species other than man.