TABLE 1

Enzyme kinetic parameters of RA isomers, 4-oxo-atRA, CRABP-bound atRA, and CRABP-bound 4-oxo-atRA as substrates with CYP26C1

Data are shown as mean ± S.D. All means are average values of three replicate experiments with each experimental datapoint determined in triplicate in each experiment. Differences in the kinetic parameters (k_cat, K_m, and Cl_int) were analyzed by one-way ANOVAs (separate ANOVA for each parameter) followed by Tukey’s multiple comparison test. Owing to the multiple ANOVA analyses, a P value of 0.01 was considered significant on the basis of a Bonferroni adjustment for multiple comparisons.

	k_cat	K_m	Cl_int
	min⁻¹	nM	μl/min per picomolar P450
atRA	5.9 ± 1.9	50.4 ± 6.2	120 ± 49
13-cis-RA	7.7 ± 2.9	38.2 ± 4.9	208 ± 101
9-cis-RA	4.7 ± 1.2	9.7 ± 2.6^{^c},^{^d}	504 ± 140^{^f}
4-oxo-atRA^{^a}		15.7 ± 4.3^{^c},^{^d}	153 ± 20
4-oxo-atRA^{^b}		10.2 ± 2.2^{^c},^{^d}
CRABPI-atRA	2.1 ± 0.2	50.8 ± 8.0^{^e}	41 ± 2
CRABPII-atRA	2.1 ± 0.8	34.1 ± 7.1^{^e}	66 ± 37
CRABPI-4oxo- atRA		3.5 ± 0.5^{^c},^{^d}
CRABPII-4oxo- atRA		5.4 ± 1.5^{^c},^{^d}

↵^a Kinetic parameters were obtained by measuring substrate depletion.
↵^b K_m value was obtained by measuring product formation.
↵^c P < 0.01, significantly different from the K_m value of atRA.
↵^d P < 0.01, significantly different from the K_m value of 13-cis-RA.
↵^e P < 0.01, significantly different from the K_m value of 9-cis-RA.
↵^f P < 0.01, the Cl_int value of 9-cis-RA is significantly different from the other Cl_int values.