Purification, ultrastructure, and chemical analysis of Alzheimer disease amyloid plaque core protein.

This is the authors' abstract. We don't add key points for this paper.

Isolation of Alzheimer disease amyloid plaque core protein (APCP) was carried out by repetitive NaDodSO4/EDTA/sucrose extractions and by Ficoll-400 density-gradient centrifugations. The enriched APCP-Ficoll interface was labeled with the fluorochrome thioflavin T and separated from the contaminating lipofuscin by fluorescence-activated cell sorting. Electron microscopy demonstrated that APCP is made of two different kinds of filaments measuring 5.5-6 nm and 10-12 nm, respectively, and of variable length. Purified APCP and lipofuscin were chemically modified by performic acid oxidation. The amino acid composition of APCP revealed a high content of glycine and valine (30%) and 1% cysteine. By contrast, the protein moiety of the copurified lipofuscin contained 16% cysteine. The amino acid composition of APCP did not resemble that of any known protein.