Table 3.

The proteolytic activity of the 3C-like proteases.

Protease	Protease activity (pmol/s)	Relative activity (%)
Wild-type	5.22 ± 0.32	100
E54A	0.45 ± 0.04	8.6
E54D	1.23 ± 0.07	23.6
E54Q	1.06 ± 0.08	20.3
E54I	0.34 ± 0.05	6.5
E54L	0.26 ± 0.04	5.0
C139S	1.02 ± 0.19	19.5
E54D,C139S	0.32 ± 0.06	6.1
E54Q,C139S	0.29 ± 0.01	5.6

The protease activity was measured in the presence of 10 µM fluorogenic peptide substrates and 5 µM purified proteases and expressed as the amount of the cleaved substrate per minute. Data are presented as means ± SE.