Separation of aminopeptidase N from Tau-cleaving activity. A commercial preparation of aminopeptidase N was fractionated on a butyl S-650 hydrophobic chromatography. (a). Tau-cleaving activity was estimated by the intensity of the remaining Tau band as analyzed by SDS-PAGE. T = Tau with buffer only. (b) Aminopeptidase N activity as determined with alanine 4MNA as substrate.