Human PSAsf preparation cleaves Tau. (a) Purity of hPSAsf (5 μg). (b) Degradation of Tau by hPSAsf. Tau was incubated with PSA at a molar ratio of 15:1 (Tau:PSA) in 10 mM Tris buffer, pH 7.5, 1 mM DTT at 37°C for 16 h. Reactions containing 1 μg Tau were analyzed by SDS-PAGE on a 12.5% gel. Labeled products and intact Tau were further analyzed by mass spectrometry and the result is shown in Table 1. (c) Reaction products immunoblotted with N-terminal Tau antibody 5A6 (red) or C-terminal Tau antibody A00024 (green). Twenty percent of the reaction mix was loaded in each lane. Intact Tau shows a yellow color due to the red/green overlap. N1 also reacts to A00024, but was overshadowed by higher intensity signal of 5A6. Molecular weight markers in kDa are shown at the left.