Fig. 5.

Influence of an n-terminal (His)₆-affinity tag and dimerization on the catalytic activity of SARS-CoV 3CLpro. Assays were performed in 100 μL reactions with 50 mM HEPES buffer, pH 7.5, using 1 μM of either the Alexa488-QSY7 or Dabcyl-EDANS FRET-peptide substrates. Data were fit to Eq. (1) and the resulting best-fit parameters for Alexa488-QSY7 were k_cat = 0.097 ± 0.009 min⁻¹ and K_d = 0.23 ± .12 μM, and for Dabcyl-EDANS were k_cat = 0.32 ± 0.06 min⁻¹ and K_d = 1.0 ± 0.5 μM.