Probable catalytic subunit of the gamma-secretase complex, an endoprotease complex that catalyzes the intramembrane cleavage of integral membrane proteins such as Notch receptors. Homodimer. Component of the gamma-secretase complex, a complex composed of a presenilin homodimer (PSEN1 or PSEN2), nicastrin, APH1 and PEN2 (Probable). Protein expression is initiated from 6 and 12 hours of embryonic development. The PAL motif is required for normal active site conformation. While the protein appears only from 6 hours of development, the transcript is maternally derived and ubiquitously expressed during early embryonic development, suggesting that its translation is strictly regulated. Belongs to the peptidase A22A family.