TABLE 3

Kinetic constants for menadione metabolism by His₆-tagged and untagged recombinant human CBR3 wild-type enzyme

Values correspond to the mean ± S.D. obtained from three experiments performed with three independent enzyme preparations (n = 9). Also presented are the kinetic constants for the His₆-tagged CBR1 wild-type human enzyme, which serves as a positive control for enzyme activity with menadione. In addition, the kinetic constants are shown from the studies by Lakhman et al. (2005) and Miura et al. (2008).

Kinetic Parameters	CBR3 Wild Type (Tagged)	CBR3 Wild Type (Untagged)	CBR1 Wild Type (Tagged)	Lakhman et al.	Miura et al.
V_max, nmol/min·mg protein	170 ± 29	149 ± 31	582 ± 43	19,600 ± 2000	126^b
K_m, μM	76 ± 23	60 ± 15	20 ± 6	25 ± 3	54 ± 10
k_cat, s⁻¹ ^a	0.096 ± 0.014	0.084 ± 0.016	0.33 ± 0.02	9.9	0.071
k_cat/K_m, s⁻¹ M⁻¹	1320 ± 290	1410 ± 400	17,400 ± 2800	402,000	1300

↵a k_cat calculated for His₆-tagged CBRs and untagged CBR3 from molecular mass of 34 and 30.9 kDa, respectively.
↵b Calculated V_max.