Fig. 1.

(A) ClpXP degradation of ³⁵S-labeled UmuD′ in UmuD/D′ heterodimers (10 μM) or ³⁵S-labeled Arc-ssrA (10 μM) was measured after 30 min (for UmuD′) or 2 min (for Arc-ssrA) in the presence of 0, 50, or 500 μM SspB XB peptide. (B) ClpXP degradation of ³⁵S-labeled UmuD′ (10 μM) was measured as a function of the concentration of UmuD (K_M = 31.8 ± 8.9 μM; V_max = 2.1 ± 0.3 min^-1·ClpX₆^-1) or UmuD^XB (K_M = 15.4 ± 3.4 μM; V_max = 2.1 ± 0.4 min^-1·ClpX₆^-1). Steady-state kinetic parameters were obtained by fits to the Michaelis–Menten equation.