Table 1. ATPase activity of CL-Pgp and low-Cys mutants.

Protein	ATPase activity* (μmole Pi/mg/min)	Ks Verapamil (μM) †	Ki Cyclosporine A (μM)‡
Wt	3.5±0.66	4.8±1.8	2.0±0.8
C6Z	3.5±0.19	2.0±1.1	3.4±0.9
CL-Pgp	3.2±0.56	3.8±3.3	4.8±2.3

*Maximum verapamil-stimulated ATPase activity in the presence of 30 μM verapamil (mean±S.E.M.).

†Concentration required for half-maximal ATPase activity derived from plots of V versus [drug] in Figures 8A and 8C (mean±S.E.M.); similar plots were obtained for C6Z-Pgp (not shown).

‡Cyclosporine A concentration required for half-maximal inhibition of verapamil-stimulated ATPase in Figures 8B and 8D (mean±S.E.M.); similar plots were obtained for C6Z-Pgp (not shown).