Aliquots of USP17 were stored at 4 °C, 25 °C, or 37 °C for 1, 2, or 3 days. At each time point the sample was centrifuged, and the remaining enzyme concentration was measured by A280 and adjusted with the determined extinction coefficient to 6.25 nM. (A) Remaining activity was measured with 0.5 μM Ub-Rho110. (B) Specific activity was calculated as described in the Materials and Methods with the same concentrations of substrate and enzyme as (A). All assays were done in triplicate. Error, Standard Deviation.