Alzheimer amyloid protein precursor (APP) is an integral membrane protein, which is subject to a covalent modification; N- and O-glycosylation in an extracellular domain of APP and phosphorylation in a cytoplasmic domain of APP.Our previous studies demonstrated that the phosphorylation at three sites in the cytoplasmic domain, Thr654, Ser655 and Thr668, is a physiological event in rat brain tissues. However, functions of APP modification in APP metabolism have not been clarified.To analyze the functions of the covalent modifications of APP in APP metabolism, various mutations were introduced into or around the phosphorylation sites in cytoplasmic domain and into the extracellular domain including the glycosylation sites of APP. The mutant APP was transfected into 293 cells and stable transfectants expressing the mutant APP were established. Utilizing anti-APP antibodies and phosphorylation state-specific antibodies raised to phosphorylation sites, detailed analyses for APP metabolism in transfectants, maturation of APP, and processing of APP, were performed and metabolic alterations of APP were tested. The data suggest an importance of covalent modification of APP in APP metabolic pathway.