Cell-permeable. An irreversible ubiquitin-activating enzyme (E1) inhibitor (IC50 < 10 μM). Blocks ubiquitylation and prevents ubiquitin-mediated proteasomal degradation. Inhibits NF-κB activation, blocks degradation of p53, increases p21 levels and induces apoptosis in vitro. Also causes an increase in sumoylation of proteins. MW: 371.3. Purity ≥98% by TLC