Abstract
Two morphologic components of human amyloid deposits, the periodic rod and the fibril, have been prepared free of cross-contamination. On tryptic digestion of guanidine-denatured material, peptide maps indicate these two components to have characteristic patterns with no detectable peptide fragments in common. Additional studies on ultrastructural morphology, physical characteristics and chemical composition reveal that the two components are clearly distinct entities with no evidence that one is a derivative of the other. The periodic rod, composed of stacked pentagonal unit structures or "doughnuts," is an antigenic globular glycoprotein deficient in tryptophan and methionine. The fibril, composed of laterally aggregated unit structures or filaments, is a poorly or nonantigenic fibrous glycoprotein of "pleated sheet" type containing both tryptophan and methionine. Congo red staining and birefringence, a dual characteristic of the fibrils and filaments, is dependent upon the physical integrity of these structures.