Probable catalytic subunit of the gamma-secretase complex, an endoprotease complex that catalyzes the intramembrane cleavage of integral membrane proteins such as Notch receptors (By similarity). May play a role in negative regulation of apoptotic cascades during oogenesis and embryogenesis, and in developmentally matured tissues such as brain tissue. Homodimer. Probable component of the gamma-secretase complex, a complex composed of a presenilin homodimer (PS-alpha or PS-beta), nicastrin (NCSTN), APH1 and PEN2 (Probable). Highest expression in ovaries and to a lesser extent in kidney, brain, eye and lung. Weak expression in testis, intestine, liver and heart. Present in trace amounts in skeletal muscle. Abundant in early stages of oogenesis after which it is nearly constant. The PAL motif is required for normal active site conformation. Belongs to the peptidase A22A family.