Table 1. Drug-stimulated ATPase activity of TM1 cysteine mutants.

ND, not determined because of very low expression.

	Verapamil		Colchicine		Vinblastine
Mutant	Vmax (%)*	S50 (μM)†	Vmax (%)	S50 (μM)	Vmax (%)	S50 (μM)
M51C	101	11.0±0.6	96	391±36	94	2.4±0.2
V52C	ND	ND	ND	ND	ND	ND
V53C	104	12.0±0.2	101	389±30	102	2.2±0.1
G54C	ND	ND	ND	ND	ND	ND
T55C	114	10.3±1.1	95	418±22	91	2.2±0.1
L56C	103	12.2±0.3	87	440±41	95	2.5±0.2
A57C	108	11.3±0.3	98	377±34	92	2.4±0.2
A58C	90	12.5±0.2	94	434±20	95	2.6±0.3
I59C	115	11.2±0.8	95	380±33	114	2.5±0.2
I60C	102	11.1±0.7	91	408±18	110	2.5±0.2
H61C	97	54.0±5.0	61	912±86	105	5.4±0.4
G62C	ND	ND	ND	ND	ND	ND
A63C	114	10.5±1.2	99	362±42	105	2.0±0.3
G64C	106	45.0±6.0	88	613±55	60	2.4±0.1
L65C	72	9.3±1.1	112	368±32	78	2.0±0.2
P66C	95	13.0±0.5	86	480±39	97	2.8±0.4
L67C	101	12.3±0.3	106	423±21	100	2.3±0.1
M68C	119	9.7±1.1	105	365±32	92	2.3±0.2
M69C	107	11.8±0.6	110	431±25	108	2.2±0.1
L70C	94	11.4±0.7	90	413±18	98	2.3±0.1
V71C	106	11.9±0.3	90	370±27	102	2.5±0.5
Cys-less	100	12.0±1.0	100	412±48	100	2.2±0.3

* Maximum activity relative to that of Cys-less P-gp.

† Substrate concentration at 50% maximal activity.