TABLE 3.

Comparison of K_D, IC₅₀, and solubility parameter values for inhibitors of Scabin

Inhibitor	KDa	IC50b	Kic	pIC50d	ΔTme
	μm	μm	μm		°C
PJ34	14 ± 0.5	12 ± 1	3 ± 0.2	4.9	2.4 ± 0.3
P6-C	25 ± 1	89 ± 4	19 ± 1	4.1	2.2 ± 0.6
P6-D	42 ± 5	97 ± 7	18 ± 1	4.0	1.8 ± 0.4
P6-E	50 ± 6	119 ± 2	24 ± 0.3	3.9	2.6 ± 0.7
P6-F	NDf	38 ± 2	7 ± 0.2	4.4	1.5 ± 0.5

^a The binding affinity of inhibitors to Scabin was measured by the quenching of the intrinsic Trp fluorescence caused by the binding of the ligand to the enzyme active site.

^b The IC₅₀ values were determined by fitting each dose-response curve to a Boltzmann sigmoidal function in MicroCal Origin version 8.0.

^c The inhibition constant (K_i) was calculated from the experimentally determined IC₅₀ values according to the relationship, K_i = IC₅₀/(1 + ([S_NAD]/K_m(NAD)) using fixed values for [Scabin] = 10 μm, [ϵ-NAD⁺] = 400 μm, and K_m(ϵ-NAD+) = 276 μm.

^d The pIC₅₀ values were calculated from the IC₅₀ values as follows, pIC₅₀ = −log IC₅₀. The higher the pIC₅₀ value, the lower dose that is required for 50% inhibition of Scabin toxin activity.

^e The ΔT_m value (°C) was determined by the expression, ΔT_{m°C(Scabin-inhibitor)} − ΔT_{m°C (Scabin-apo)}.

^f Not determined.