Amyloid. 3. A protein related to the subunit structure of human amyloid fibrils.

Abstract

A characteristic protein component obtained from tissues of patients with secondary amyloid has been purified and some of its characteristics including molecular weight and amino acid composition determined. The protein is roughly globular, has a molecular weight of about 13,500, and an amino acid compositin in which threonine, cystine, and cystelne appear to be absent; tyrosine and tryptophan are present to the extent of 7 and 3 residue weight percents, respectively. This protein fits in size and configuration the dimensions of the subunlts which seem to comprise amyloid fibrils observed In situ and in isolated amyloid fibrils observed with the electron microscope. The arrangement of the subunlts in the amyloid fibrils may be either in a helix or the "stacked-disk" form. Identification of a possible protein subunit and approximate ultrastructure of the amyloid fibrils suggest several possibilities in regard to cause and pathogenesls of this disease process: that the protein of amyloid represents a virus coat protein; that It Is a normal cell protein produced In abnormal amounts under conditions leading to amyloid formation; that It Is an abnormal entity produced in geneticaUy defective cells or cells under chronic stress; that it Is a fragment of a larger normal entity, e.g., the protein moiety of a mucopolysaccharide.