Properties of caspases that confound interpretation of assays using substrate motif-based activity probes and inhibitors. (A) Caspase A has a greater expression level than caspase B. (B) Caspase D has altered substrate specificity when in an intermediate activation step (D*) compared to the fully mature enzyme. (C) Caspase E is able to cleave many different substrates while caspase F cleaves only one particular substrate. (D) Caspase G is able to cleave many substrates in the same amount of time caspase H cleaves one substrate.