Structural similarities between a protein extracted from normal human tissues and a component of amyloid fibrils.

Comparative immunologic and chemical studies of crude or fractionated amyloid fibrils and materials obtained from corresponding normal tissues have been performed. Materials from the amyloidotic and normal tissues were subjected to identical methods of extraction, chemical treatment and protein fractionation. Antigenic similarities between crude amyloid fibrils and corresponding normal tissue extracts were observed, however, a considerably larger concentration of the latter antigens was needed to obtain immunologic reactivity in double diffusion in gel. Striking similarities were observed when the amino acid composition of a high molecular weight subcomponent of amyloid fibrils was compared with that of normal tissue extracts. Crude, intact amyloid fibrils were highly effective in absorbing Congo-red while the ability to absorb Congo-red was by far less if the high molecular weight subcomponent of amyloid fibrils as well as the corresponding normal tissue extracts were used. The high molecular weight subcomponent of amyloid, which seems to be an integral part of the amyloid fibrils, most probably is a protein derived from normal tissue.