Table 1.

Summary of the inhibitory potencies (EC₅₀) of S1QELs

The EC₅₀ value is the molar concentration (μm) needed to reduce the control NADH oxidase activity (forward electron transfer) or ubiquinol-NAD⁺ oxidoreductase activity (reverse electron transfer) in SMPs by 50%, except for S1QEL1.5 and S1QEL1.5_D1. SMPs concentrations are 30 and 100 μg of proteins/ml for forward and reverse electron transfer measurement, respectively. The EC₅₀ values that were normalized by protein concentrations (nmol of inhibitor/mg of proteins) are also listed in the parentheses. Values are mean ± S.E. (n = 3–4).

S1QELs	Forward electron transfer EC50 (μm) (nmol inhibitor/mg of proteins)	Reverse electron transfer EC50 (μm) (nmol inhibitor/mg of proteins)	Ratioa (forward/reverse)
S1QEL1.1	0.059 ± 0.006 (2.0 ± 0.20)	0.038 ± 0.005 (0.38 ± 0.05)	5.2
S1QEL1.5	1.9 ± 0.38b (63 ± 13)	0.31 ± 0.07c (3.1 ± 0.7)	20
S1QEL2.1	0.29 ± 0.044 (9.7 ± 1.5)	0.060 ± 0.003 (0.60 ± 0.03)	16
S1QEL2.3	0.54 ± 0.08 (18 ± 2.8)	0.13 ± 0.02 (1.3 ± 0.20)	14
S1QEL1.5_D1	1.4 ± 0.16b (47 ± 5.2)	0.24 ± 0.047c (2.4 ± 0.47)	20
S1QEL1.1_D1	0.89 ± 0.04 (30 ± 1.0)	1.25 ± 0.06 (12.5 ± 0.6)	2.4
S1QEL1.1_D2	0.88 ± 0.07 (29 ± 2.0)	0.50 ± 0.02 (5.0 ± 0.2)	5.8
S1QEL1.1_D3	0.32 ± 0.02 (11 ± 0.6)	0.43 ± 0.04 (4.3 ± 0.4)	2.5
Bullatacin	0.0020 ± 0.0002 (0.070 ± 0.007)	0.0046 ± 0.0006 (0.046 ± 0.006)	1.4

^a The ratio of EC₅₀ (forward)/EC₅₀ (reverse) values in terms of nanomole of inhibitor/mg of proteins.

^b The EC₅₀ value was expediently evaluated from the inhibition observed at ∼1 min after the addition of a test compound during catalytic turnover; namely, we read a slope of the dotted line indicated for trace c in Fig. 2.

^c Because the maximum inhibition by this compound was ∼40% (Fig. 4B), the molar concentration that attained 20% inhibition was determined.