Ultrastructural study of enriched fractions of "tangles" from human patients with senile dementia of the Alzheimer type.

Enriched fractions of "tangles" obtained from cases of Alzheimer's disease have been observed by negative staining and platinum: iridium shadowing, and also after treatment with sodium dodecyl sulfate and urea. Abnormal filaments with a 80-nm periodic constriction exhibited a substructure consisting of six protofilaments. They also showed a periodic right-handed twist. Some fibrils with a 160-nm periodic constriction were made up of four protofilaments. These features are discussed in view of known fibrous protein models, especially neurofilaments.