Table 1

Apparent kinetic parameters for the N-glucuronidation of (R)- and (S)-ketotifen and amitriptyline in homogenates or membranes of cells expressing UGT1A4 or UGT1A3 and in human liver microsomes

Substrate	Expressed UGT1A4		Expressed UGT1A3		Liver Microsomes
	K_M	V_max	K_M	V_max	K_M1	K_M2	V_max1	V_max2
(R)-Ketotifen	59 ± 5	130 ± 20	180; 270	5.4; 6.5	2.4 ± 1.2	22 ± 16	85 ± 21	113 ± 54
					15 ± 2^1-a		470 ± 90^1-a
(S)-Ketotifen	86 ± 26	140 ± 20	96; 150	9.5; 14	1.0	160	37	165
					1.3 ± 0.3^1-a	92 ± 47^1-a	60 ± 20^1-a	440 ± 100^1-a
Amitriptyline	100 ± 10	340 ± 30			0.4; 2.1	520; 470	27; 25	650; 550
					1.4 ± 0.2^1-a	310 ± 20^1-a	8.4 ± 5.4^1-a	250 ± 190^1-a

K_M values are given in micromolars,V_max in picomoles per minute per milligram of protein. When mean ± S.D. is given, N = 3 or 4. Kinetic data for (R)- and (S)-ketotifen in liver microsomes are taken from Mey et al. (1999), those for amitriptyline in the presence of Triton from Breyer-Pfaff et al. (1997).

↵1-a Triton X-100 0.02% as detergent