DENV-2 NS2b-NS3Pro enzyme assay, optimization and validation. (A) Kinetics of NS2b-NS3Pro action as a function of substrate concentration (at 5nM enzyme). (B) Rate of enzyme catalysis as a function of enzyme concentration (at 10 μM substrate). (C) Activity of the cloned NS2b-NS3Pro as function of aprotinin concentration (5nM enzyme, 10 μM substrate, 20 min incubation). Activity in the absence of aprotinin was taken as 100% (RFU = relative fluorescence units).