FIG. 4.
NA enzyme kinetics of the recombinant viruses, showing the substrate conversion velocity (V0 ) of NA as a function of substrate concentration. (A) Recombinant VN1203, VN1203-H274Y, VN1203-N294S, and PR8 viruses; (B) recombinant PR8 viruses. The fluorogenic MUNANA substrate was used at final concentrations of 0 to 3333 μM. All recombinant viruses were standardized to an equivalent virus dose of 107.5 PFU/ml. The reaction was conducted at 37°C, and fluorescence was measured every 92 s for 45 min using excitation and emission wavelengths of 355 and 460 nm, respectively.