Table 2.

Comparison of kinetic constants for CYP3A4, CYP21A2, and CYP17A1 expressed with either bacterial endogenous FePPIX biosynthesis or the addition of exogenous FePPIX and heme uptake genes

CYP17A1 and CYP21A2 were evaluated using a progesterone C17- and C21-hydroxylation assay, respectively, whereas CYP3A4 was evaluated using a luciferin–isopropyl alcohol substrate. Values are reported for protein expressed in the absence or presence of the stabilizing substrate progesterone for the two steroidogenic enzymes.

	kcata	Km	kcat /Km
	min−1	mm	min−1 mm−1
CYP3A4 expressed with:
Endogenous FePPIX	0.0064 ± 0.0002	5.2 ± 0.6	0.0012
Exogenous FePPIX	0.0074 ± 0.0004#	4.7 ± 0.7	0.0015
CYP21A2 expressed with:
Endogenous FePPIX	20 ± 1	3.2 ± 0.7	6.2
Exogenous FePPIX	19 ± 1	2.8 ± 0.6	6.9
Endogenous FePPIX/progesterone	20 ± 1	2.8 ± 0.7	7.2
Exogenous FePPIX/progesterone	20 ± 1	2.9 ± 0.7	6.7
CYP17A1 expressed with:
Endogenous FePPIX	2.9 ± 0.7	2.5 ± 0.3	1.1
Exogenous FePPIX	1.3 ± 0.4##	2.5 ± 0.3	0.50
Endogenous FePPIX/progesterone	3.1 ± 0.1	2.2 ± 0.4	1.4
Exogenous FePPIX/progesterone	1.8 ± 0.1##	2.9 ± 0.6	0.63

^a #, p < 0.05; ##, p < 0.01 compared with the K_m and k_cat of the same enzyme expressed with endogenous FePPIX biosynthesis.