GSK-3β phosphorylation of tau isoforms visualized by changes in gel mobility and phosphate incorporation. (A) The migration of GSK-3β phosphorylated tau isoforms (p) was compared to unphosphorylated isoforms (up) by Coomassie-stained SDS-PAGE. The isoforms are labeled above their respective lanes. 2N4R was analyzed on a separate gel and then aligned by its relative migration to molecular weight standards. (B) γ-32P ATP was added to the phosphorylation reaction overnight and moles of phosphate per mole of tau was calculated by averaging 4 trials ± SEM. Each isoform in (B) is individually labeled underneath its respective value.