Reaction of Tau with various forms of PSA. Same amount of PSA activity was reacted with Tau 2N4R or Tau 0N4R in 10 mM Tris buffer, pH 7.5, 1 mM DTT at 37°C for 16 h. (a). Reaction mixtures were analyzed by SDS-PAGE, only Tau 2N4R is shown. (b). For quantitation, the intensity of Tau remaining was determined using ImageJ software . For internal control, a 50% Tau alone (last lane) was run and the band intensity shown to be ~50% of the input Tau (first lane). Further, by analyzing the staining intensity of the PSA bands we calculated that the variation in the amount of PSA added in each lane varied less than 4%. For the GST-PSA lane, both GST-PSA and free PSA were present. Their intensities were combined to get total PSA. * = free GST.