The fluorescent characterization of the polymerized microtubule-associatedprotein Tau

A new fluorescence formed while microtubule-associated protein tau was incu bated at 25 and 37 degrees C for hours, with its maximum excitation at 230 and 280 nm, respectively. The fluorescence completely formed after tau was incubated in phosphate buffer and Tris-HCl buffer for approximately 20 h, w ith a relaxation phase about 2-4 h. The light scattering of the sample solu tion improved during formation of the fluorescence when tau was incubated. Both the fluorescence and tau oligomers did not form when tau was incubated in the buffers containing DTT. On the other hand, heparin improved both ta u aggregation and the fluorescence formation. It suggests that the fluoresc ence comes from tau polymerization, which may follow the mechanism of tyros ine-tyrosinate emission for a protein not containing any tryptophan residue s. This new fluorescence could be used as a probe to tau polymers. (C) 2000 Elsevier Science B.V. All rights reserved.