NSC632839 is a nonselective isopeptidase inhibitor, which inhibits USP2, USP7, and SENP2 with EC₅₀s of 45±4 μM, 37±1 μM, and 9.8±1.8 μM, respectively. IC50 & Target: EC50: 45±4 μM (USP2), 37±1 μM (USP7), 9.8±1.8 μM (SENP2)^[1] In Vitro: NSC 632839 inhibits ubiquitin isopeptidases as illustrated by its ability to inhibit z-LRGG-AMC cleavage by crude lysates in the mid-micromolar range. To further characterize NSC 632839 against purified enzymes, its inhibitory potential is determined against purified USP2, USP7, and SENP2 and demonstrated that NSC 632839 is not only a DUB inhibitor, but also a deSUMOylase inhibitor. Specifically, NSC 632839 inhibits USP2, USP7, and SENP2 with EC₅₀ values of 45±4 μM, 37±1 μM, and 9.8±1.8 μM, respectively. Importantly, NSC 632839 does not inhibit the reporter enzyme PLA₂ over the concentration range tested (1.2-150 μM), indicating that the reported inhibition is selective for isopeptidases. Moreover, the isopeptidase inhibitory activity of NSC 632839 is confirmed by the observation that it does not inhibit free PLA₂ over the concentration range tested^[1].