Table 2. Michaelis-Menten parameters for ABCB7 variants in the presence of [2Fe–2S](GS)₄.

The K_M for Mg-ATP and V_max of ATPase activity was determined using the EnzChek Phosphate Assay Kit in the presence and absence of 10 μM [2Fe–2S](GS)₄ cluster. In the presence of cluster, the K_m for Mg-ATP increased, while this was not observed in any of the substituted derivatives. The V_max was observed to increase in both the native and E433D derivative in the presence of cluster. This observation is consistent with the cluster dependence on ATPase activity (Table 1) and the ability to transfer cluster (Fig. 4).

	Mg-ATP KM (mM)	Mg-ATP Vmax (μM/min)	Mg-ATP KM (mM) w/10 μM cluster	Mg-ATP Vmax (μM/min) w/10 μM cluster	fold increase in kcat/KM in presence of cluster
native	5.3 ± 1.0	0.58 ± 0.04	0.54 ± 0.23	0.68 ± 0.03	11.5
E433D	0.85 ± 0.28	0.35 ± 0.03	2.1 ± 0.2	0.79 ± 0.03	0.92
E433K	0.49 ± 0.11	0.37 ± 0.02	1.1 ± 0.3	0.32 ± 0.03	0.40
E433Q	0.71 ± 0.30	0.28 ± 0.04	1.1 ± 0.2	0.31 ± 0.01	0.72