The purification of tau protein and the occurrence of two phosphorylation states of tau in brain.

Two newly discovered properties of tau protein are reported; it is soluble in 2.5% perchloric acid and insoluble in 25% glycerol. These properties were exploited in the development of improved methods for the purification of tau. Treatment with perchloric acid did not alter the electrophoretic behavior of tau, and the products of the new isolation method were fully competent in the promotion of microtubule assembly. The application of the new purification techniques to bovine brain tissue demonstrated that tau exists endogenously in the dephosphorylated as well as in a phosphorylated state.