Ac-YVAD-AFC is a substrate whose amino acids YVAD have been shown to be a preferred cleavage site for caspase-1 and -4.1,2 Caspase activity can be quantified by fluorescent detection of free AFC (also known as 7-amino-4-trifluoromethylcoumarin), which is excited at 400 nm and emits at 505 nm.