Figure 4.

Persistent inhibition of M^pro and papain activity by celastrol. (a) Assay procedure to determine the irreversibility of M^pro and papain inhibition by celastrol. The enzymes were incubated for 30 min with buffer (control) or 22 mM celastrol, as indicated in the Methods section. Part of the incubation mixture was kept on ice and the other part was submitted to three ultrafiltration cycles to remove free celastrol and concentrate the enzymes. The M^pro and papain activity was determined in the concentrate. (b) M^pro and (c) papain activity before and after repeated dilution/filtration cycles. M,^pro main protease.