Gel electrophoretic distinction between toxic and nontoxic forms of beta-amyloid (1-40)

The in vitro toxicity of synthetic beta-amyloid (1-40) correlates with its binding to Congo red (CR). Potentially, therefore, CR binding to the beta-a myloid containing neuritic plaques in Alzheimer's disease could be used dia gnostically. Using polyacrylamide under nondenaturing conditions, the prese nt study shows that both CR binding and nonbinding synthetic beta-amyloid e xhibits multiple charge-isomeric and size;isomeric species. The CR binding species exhibit values of free electrophoretic mobility, related to the sur face charge density of the protein, which are less than those of the CR non binding species within 95% confidence limits. Since surface net: charge and solubility are correlated, the decreased solubility of the CR binding spec ies may be responsible for the relative abundance and CR binding of beta-am yloid in the neuritic plaques of Alzheimer patients.