Presenilin 1 and presenilin 2 are transmembrane proteins belonging to the presenilin family. Mutation of presenilin genes has been linked to early onset of Alzheimer’s disease, probably functioning throμgh its associated g-secretase activity for amyloid-β protein processing. Endogenous presenilin mainly exists in a heterodimeric complex formed from the endoproteolytically processed N-terminal (34 kDa) and C-terminal (~20 kDa) fragments.