A preparation of Alzheimer paired helical filaments that displays distinct tau proteins by polyacrylamide gel electrophoresis.

Paired helical filaments (PHFs) are prominent components of Alzheimer disease (AD) neurofibrillary tangles (NFTs). Rather than isolating NFTs, we selected for PHF populations that can be extracted from AD brain homogenates. About 50% of PHF immunoreactivity can be obtained in 27,200 x g supernatants following homogenization in buffers containing 0.8 M NaCl. We further enriched for PHFs by taking advantage of their insolubility in the presence of zwitterionic detergents and 2-mercaptoethanol, removal of aggregates by filtration through 0.45-microns filters, and sucrose density centrifugation. PHF-enriched fractions contained two to five proteins of 57-68 kDa that displayed the same antigenic properties as PHFs. Since the 57- to 68-kDa PHF proteins are antigenically related to tau proteins, they are similar to the tau proteins previously observed in NFTs. However, further analysis revealed that PHF-associated tau can be distinguished from normal, soluble tau by PHF antibodies that do not recognize human adult tau and by one- and two-dimensional PAGE.