Carbohydrate-Containing AL Proteins

Abstract

In a previous chapter the chemical and ultrastructural aspects of amyloid have been discussed. Thus in primary and myeloma-associated amyloidosis, the fibrils consist mainly of immunoglobulin light chains or fragments thereof called AL proteins. Structurally, these amyloid fibril proteins are a very heterogeneous group. The AL proteins are derived from different subgroups of both к and λ chains and have a molecular mass from about 5 to 22 Kdalton (1,2). A common feature with these proteins is the ability to form fibrils. The structural studies here described were performed on the main fraction of AL proteins. Acid hydrolyzed protein samples were analyzed by an automatic amino acid analyzer. The content of hexosamine was used as an indicator of carbohydrate. Hexosamine is the most commonly found monosaccharide residue directly linked to the polypeptide chain in mammalian proteins and is also the least likely to be removed by glycosidases present in the different amyloid tissues. AL proteins isolated from amyloid fibrils prepared from different organs of 17 patients were characterized by Edman degradation, molecular weight determinations, amino acid composition and by a complete carbohydrate composition.