. Author manuscript; available in PMC: 2017 Nov 24.

Published in final edited form as: Biochemistry. 2017 May 4;56(19):2506–2517. doi: 10.1021/acs.biochem.6b01245

Table 1.

Kinetic Parameters for Substrate Inhibition (two binding sites) of ATPase Activity with Drugs and Fluorescent Analogues

	V₁ (nmol of P_i min⁻¹ mg⁻¹)	V₂ (nmol of P_i min⁻¹ mg⁻¹)	K₁ (μM)	K₂ (μM)
DMPC Nanodiscs
verapamil	1004 ± 160	>0^a	55.7 ± 14.8	118.9 ± 38.8
BD-verapamil	492 ± 10	107 ± 13	0.08 ± 0.008	12.1 ± 1.6
vinblastine	276 ± 31	>0^a	2.6 ± 1.0	40.1 ± 9.7
BD-vinblastine	105^b	21 ± 4	0.04 ± 0.01	0.7 ± 0.1
paclitaxel	199 ± 23	48 ± 6	1.3 ± 0.5	16.3 ± 24.7^c
Flutax-2	65^b	18 ± 2	0.3 ± 0.7^d	13.8 ± 3
E. coli Lipid Nanodiscs
BD-verapamil	627.5 ± 11.2	218.4 ± 223.9	0.07 ± 0.02	113.5 ± 118.4^c
BD-vinblastine	465^b	156.5 ± 24.8	0.05 ± 0.1^d	1.1 ± 0.4
Flutax-2	500^b	33.2 ± 46.8	0.2 ± 0.3^d	2.6 ± 0.9

The parameter is reaching a constraint set at >0.

The parameter held at a constant value.

Large errors due to only modest inhibition at the highest drug concentration used.

Ambiguous, because of a lack of ATPase stimulation by these ligands (V₁ is close to V₀). Fits for the DMPC nanodiscs and E. coli nanodiscs with three probes are shown in Figure 4.