TABLE 3

Kinetic constants (±S.E.) for S- and R-propranolol glucuronidation by recombinant human UGTs 1A9, 1A10, 2B4, and 2B7

The initial rate data were fitted to eqs. 1 to 3 and the kinetic constants were derived from the best fit. In case there was no significant difference between the tested equations, the simpler one (Michaelis-Menten) was selected.

	S-Propranolol			R-Propranolol
	V_max	K_m or S₅₀	V_max	K_m or S₅₀
	pmol/mg/min	mM	pmol/mg/min	mM
UGT1A9	35.3 ± 3.7	0.2^a ± 0.04	2.0 ± 0.2	0.1 ± 0.04
UGT1A10	11.4 ± 0.7	0.3 ± 0.06	81.6 ± 4.8	0.5 ± 0.1
UGT2B4^b	25.6 ± 2.4	2.6 ± 0.5	17.9 ± 0.7	1.4^c ± 0.1
UGT2B7	73.4 ± 4.4	0.6 ± 0.1	N.D.

N.D., not determined.
↵ a Substrate inhibition. K_si = 1.2 ± 0.2.
↵ b Saturated concentration not reached; experimental data up to 5 mM were fitted to the equations.
↵ c Hill equation. n = 1.9 ± 0.2.