Derived kinetic parameters for niflumic acid inhibition of recombinant and human liver microsomal UGT1A1, UGT1A9, and UGT2B15 activities

Data are presented as parameter ± S.E. of parameter fit.

Enzyme Source	Substrate	Mechanism of Inhibition	K_i^{^a}	K_i′^{^b}
			μM
UGT1A1	4MU	Noncompetitive	14 ± 0.1	N.A.
UGT1A1	β-E2	Mixed	18 ± 1.3	19 ± 1.1
HLM	β-E2	Mixed	15 ± 1.2	34 ± 3.0
UGT1A9	4MU	Mixed	0.11 ± 0.01	0.30 ± 0.14
UGT1A9	PRO	Mixed	0.10 ± 0.002	0.7 ± 0.11
HLM	PRO	Mixed	0.40 ± 0.05	1.6 ± 0.12
UGT2B15	4MU	Competitive	62 ± 2.6	N.A.

N.A., not applicable.
↵ K_i is the dissociation constant for the EI and ESI complex in noncompetitive and the EI complex in mixed inhibition.
↵ K_i′ is the dissociation constant for the ESI complex in mixed inhibition.