Chemical classes of amyloid substance.

Concentrates of amyloid substance derived from organs of 10 human patients representing a variety of clinical entities were characterized according to their amino acid compositions, their electrophoretic constituents mobile in urea-starch gel at pH 3 and their stability with respect to the binding of Congo red in the pH interval 9-12.5. The analyses revealed the existence of two major classes of amyloid substance. Material from one class, embracing those cases that had a chronic inflammatory disease as the principal associated process (type A amyloidosis), had a similar amino acid composition and was distinguished by the presence in the amyloid substance of a large amount of an electrophoretically well-defined group of low-molecular-weight proteins with an unusual amino acid composition (amyloid protein A); type A amyloid substance lost the typical binding of Congo red dye at pH 11.5 or lower. Concentrates of amyloid substance in the other class (type B amyloidosis), represented by a case of multiple myeloma, 3 other cases of neoplastic disease and a case of primary cardiac amyloidosis, were distinguished by the presence of an electrophoretically more heterogeneous group of protein constituents with different mobilities and with apparently higher molecular weights than that of protein A, by an amino acid composition that is clearly different from that of the first class, and by retention of the typical Congo red-binding property at pH 12 or higher. The major constituent, protein A, of amyloid substances of the first class is clearly different from ordinary fragments of immunoglobulins in size, electrophoretic mobility, and amino acid composition.