Fig. (4). Kinase activity of GSK 3β wt or its SUMO mutant The immunopurified Ha -GSK 3β wt or its SUMO mutant (K292R) protein with Ha Ab from COS-1 was immunoblotted with GSK 3β (A) or Anti- GSK 3β Tyr 216 phospho Ab polyclonal antibody (B). The relative optical density (OD), as determined by image analysis with the Fuji Image Quant software, is indicated below. The GSK 3β kinase activity was measured using human Tau protein as a substrate (C). S422 residue phosphorylation of human Tau protein was detected with its specific antibody. The relative GSK 3β activity by image analysis with the Fuji Image Quant software is indicated below. Results shown are one of five repeated experiments