DETECTION OF D-ASPARTATE IN TAU-PROTEINS ASSOCIATED WITH ALZHEIMER PAIRED HELICAL FILAMENTS

Paired helical filaments (PHF) characteristic of Alzheimer neurofibril lary lesions are known to contain a modified form of microtubule assoc iated protein tau. These proteins, PHF-tau, differ from normal tau in the extent and the site of phosphorylation. To determine whether PHF-t au, tau proteins from normal adult brains (N-tau), tau proteins from A lzheimer brains not associated with PHF (A-tau), and tau proteins from fetal brains (F-tau) differ in racemization, these proteins were comp ared for their D-aspartate content. The results demonstrated that PHF- tau contain more D-aspartate than N-tau, A-tau and F-tau. The average percentage D-aspartate for these proteins, after a correction for back ground, are 4.9%, 2.8%, 1.6%, and 1% for PHF-tau, N-tau, A-tau and F-t au, respectively. It remains to be determined if the increase in D-asp artate is a consequence of PHF formation. It is also unknown if the ch ange in D-aspartate content in PHF-tau is associated with phosphorylat ion, which alters the susceptibility of tau to proteolysis.