Methods

Fluoresence spectroscopy
Used a fluorogenic substrate
Suc-LLVY-AMC
Excite at 340 nm, observe emission above 350 nm
Quantify using standard curve

Potential problems with this substrate
Only release of first product observable (AMC)
Only one type of cleavage event is observed (Y-AMC bond)
P1' position is not a peptide-like entity