To explore the association between the abnormal phosphorylation sites found in Alzheimer disease （AD） 蚲 and the inhibition of its biological activit y. Methods. Ultracentrifugation

chromatography

manual Edman degradation and autos equence techniques were used to prepare and phosphorylate human recombinant 蚲

isolate and purify 32P 蚲 peptides and determine phosphorylation sites. Results. Phosphorylation of 蚲 by casein kinase 1 （CK 1）

cyclic AMP dependent protein kinase （PKA） and glycogen synthetase kinase 3 （GSK 3） separately inhi bited its biological activity and the inhibition of this activity by GSK 3 was significantly increased if 蚲 was prephosphorylated by CK 1 or PKA. The most po tent inhibition was seen by a combined phosphorylation of 蚲 with PKA and GSK 3 . The treatment of 蚲 by PKA and GSK 3 combination induced phosphorylation of 蚲 at Ser 195

Ser 198

Ser 199

Ser 202

Thr 205

Thr 231

Ser 235

Ser 262

Ser 356

Ser 404

whereas Thr 181

Ser 184

Ser 262

Ser 356 and Se r 400 were phosphorylated by GSK 3 alone under the same condition. Conclusion. Phosphorylation of 蚲 by PKA plus GSK 3 at Thr 205 might play a ke y role in 蚲 pathology in AD.