Which of the following caspases is an initiator caspase?: (A) Caspase 3, (B) Caspase 6, (C) Caspase 9, (D) None of the above
Answer is C. The caspase family, now including more than 10 members, can be divided functionally into two groups--initiator and executioner--depending on the order in which they are activated during apoptosis. Initiator caspases include caspase-8 and caspase-9. Several other caspases, including caspase-3 and caspase-6, serve as executioners. Ref: Robbins, 8th edition, Chapter 1.