Initial velocity patterns of Mpro (A–C) and dependence of the initial velocity of Mpro on enzyme concentration (D–F). (A–C) Plots of the velocity difference at various substrate concentrations for wild-type, R298A, and R298L mutants, respectively. The lines represent results fitted according to the Michaelis-Menten equation (Eq. 1) for wild-type and the Hill equation (Eq. 2) for mutants. The kinetic parameters are shown in Table 1. (D–F) Difference in velocity at various enzyme concentrations for wild-type, R298A, and R298L mutants, respectively. The concentration of substrate was 600 μM. The line represents the best fit to the nonlinear dependence equation (Eq. 3).