Fig. 3.

Dependence of SARS protease reaction rate on enzyme concentration. The 5–150 nM SARS main protease as shown in (A) and 50–3000 nM as shown in (B) with 60 μM fluorogenic substrate were used to determine the K_d value of dimer–monomer equilibrium. From (A), the K_d was determined to be 15 ± 4 nM by fitting the data to Eq. (3) (see Materials and methods). At the protein concentrations from 50 to 3000 nM (significantly larger than the K_d value), the fitting curve is almost linear.