Changes in conformation of human neuronal tau during denaturation in formaldehyde solution.

Human neuronal tau was incubated in formaldehyde solution at low concentrations and the intensity of light scattering of tau-40 solution at 480 nm increased markedly. Then potassium iodide was used to quench the intrinsic fluorescence of tau. The fluorescent quenching constants decreased as formaldehyde concentrations increased. 8-anilino-1-naphthalenesulfonic acid (ANS) binding assay showed that a putative hydrophobic core formed in tau polymers during incubation with formaldehyde. Native tau was hydrolyzed by immobilized earthworm fibrinolytic enzyme-II (EFE-II), producing a digested fragment (36-37 kDa). However, formaldehyde-treated tau could not be digested under the same conditions, suggesting that aggregated protein was relatively rigidly deposited.