TABLE 5

Derived kinetic constants for 4-MU glucuronidation by UGT1A3 and UGT1A4 chimeras and mutants Data shown as parameters ± S.E. of parameter fit.

Enzyme	K_m^a or S₅₀^b	K_si ^a	Hill coefficient (n_H)^b	V_max ^c	CL_int^d or CL_max^e
	μM	μM		pmol/min/mg	μl/min/mg
UGT1A3	1205 ± 37^a	916 ± 30		1273 ± 41	1.06^d
UGT1A3–4	781 ± 10^a	1931 ± 35		767 ± 2	0.98^d
UGT1A3–4-3	702 ± 71^a	1496 ± 193		613 ± 2	0.87^d
UGT1A3(I36T)	994 ± 39^b		1.57 ± 0.06	115 ± 1	0.06^e
UGT1A3(H40P)	1493 ± 93^b		2.12 ± 0.15	15 ± 0.5	0.01^e
UGT1A4	N.A.	N.A.	N.A.	N.A.	N.A.
UGT1A4–3	1012 ± 29^b		2.29 ± 0.14	24 ± 0.2	0.02^e
UGT1A4–3-4	848 ± 102^a	2393 ± 160		87 ± 11	0.10^d
UGT1A4(T36I)	537 ± 6^a	1680 ± 32		98 ± 1	0.18^d
UGT1A4(P40H)	N.A.	N.A.	N.A.	N.A.	N.A.