Deamidation of N279 reduced the functional activity of tau. Effects of deamidation at N279 on the ability of four repeat htau46 (412 amino acid isoform of human tau) to promote microtubule assembly (a) and to bind to microtubules (b, c). a, Polymerisation of tubulin induced by wild-type htau46 (solid line) and htau46 N279D (dotted line) was monitored by turbidimetry. Results of a typical experiment are shown; similar results were obtained in three separate experiments. b, SDS-PAGE and CBB stainings of free tau and tau bound (arrows) to a constant amount of tubulin (small arrow) are shown. c, Scatter plots of quantitations of free tau and tau bound to WT tau (open circles) and N279D mutant tau (open squares).