Table 1.

Reported k_cat and apparent K_m values for human cytochrome P450 reactions in steroid and sterol metabolism.

Enzyme	Substrate →Product	kcat	Km	ref
CYP3A4	testosterone →6β-testosterone	1.3 s−1	23 μM	[43]
CYP7A1	cholesterol →7α-hydroxycholesterol	3.1 s−1	1.3 μM	[44]
CYP11A1a	cholesterol →pregnenolone	0.021 s−1	14 μM	[45]
CYP11A1	20R,22R-dihydroxycholesterol →pregnenolone	4.1 s−1	10 μM	[46]
CYP11B1	11-deoxycorticosterone →corticosterone	1.35 s−1	--	[47]
CYP11B1	11-deoxycortisol →cortisol	1.61 s−1	--	[47]
CYP11B1	corticosterone →18-hydroxycorticosterone	0.008 s−1	--	[47]
CYP11B2	11-deoxycorticosterone →corticosterone	0.63 s−1	--	[47]
CYP11B2	corticosterone →aldosterone	0.011 s−1	--	[47]
CYP17A1b	pregnenolone →17-hydroxypregnenolone	0.037 s−1	0.65 μM	[48]
CYP17A1c (+b5)	pregnenolone →17-hydroxypregnenolone	0.065 s−1	0.65 μM	[48]
CYP17A1b	progesterone →17-hydroxyprogesterone	0.056 s−1	1.0 μM	[48]
CYP17A1c (+b5)	progesterone →17-hydroxyprogesterone	0.078 s−1	1.0 μM	[48]
CYP17A1c,d (+b5)	17-hydroxypregnenolone →DHEA	0.041 s−1	1.2 μM	[48]
CYP17A1c,d (+b5)	17-hydroxyprogesterone →androstenedione	0.030 s−1	5.0 μM	[48]
CYP19A1	androstenedione →estrone	0.060 s−1	44 nM	[22]
CYP19A1	19-oxoandrostenedione →estrone	0.42 s−1	18 μM	[22]
CYP21A2	progesterone →11-deoxycorticosterone	2.8 s−1	0.21 μM	[28]
CYP21A2	17-hydroxyprogesterone →11-deoxycortisol	4.0 s−1	1.5 μM	[28]
CYP24A1	1,25-dihydroxyvitamin D3 →1,24,25-trihydroxyvitamin D3	0.44 s−1	--	[49]

Only the separate k_cat and K_m values are considered and not the ratio k_cat/K_m [50, 51]; DHEA, dehydroepiandrosterone

^arate of a 3-step reaction

^bwithout cytochrome b₅

^cwith cytochrome b₅