(A) Substitution of the native cysteines with alanines marginally reduces the Vmax of ATP turnover. The solid line is a non-linear least-squares fit that yields Vmax (48.52 ± 1.85 nmol/min/mg), Km (1.19 ± 0.13 mM) for BmrCD-WT (basal); Vmax (72.39 ± 2.86 nmol/min/mg), Km (1.35 ± 0.14 mM) for BmrCD-WT (in presence of Hoechst) and Vmax (36.02 ± 1.51 nmol/min/mg), Km (1.08 ± 0.17 mM) for BmrCD-WT* (basal); Vmax (56.86 ± 2.47 nmol/min/mg), Km (1.6 ± 0.27 mM) for BmrCD-WT* (in presence of Hoechst 33,342). Vmax and Km values for BmrCD-WT, BmrCD-WT* and spin-labeled BmrCD are the average of three independent measurements. (B) All spin-labeled BmrCD pairs used for this study turnover ATP well above the background observed from inhibition by vanadate. Vmax increased for all pairs following the addition of Hoechst although the level of stimulation was somewhat variable.