FIG. 1.
NA enzyme kinetics of five H5N1 influenza viruses. The velocity of substrate conversion by NA (Vo) is shown as a function of substrate concentration and expressed in the conversion of the MUNANA concentration (fluorescence units) per second. Fluorogenic MUNANA substrate was used at a final concentration of 0 to 3,333 μM. The viruses were standardized to an equivalent dose of 107.5 PFU/ml. Fluorescence was measured every 92 s for 45 min at 37°C, using excitation and emission wavelengths of 355 and 460 nm, respectively. The curves representing NA enzyme kinetics of the five H5N1 influenza viruses were drawn by approximation of Michaelis-Menten equation by using nonlinear regression.