Table 1.

Progesterone 17α-hydroxylation activities of P450 17A Arg/Cys mutant proteins

All rates were measured in the presence of an equimolar concentration of b₅ relative to P450 (human b₅ was used with human P450 17A1, and zebrafish b₅ was used with zebrafish P450s), with a 2-fold molar excess of NADPH-P450 reductase and equimolar concentration of b₅ when indicated.

	Human P450 17A1		Zebrafish P450 17A1		Zebrafish P450 17A2
	WTa	R358C	WTb	R369C	WTb	C358R
kcat, min−1	10.2 ± 0.6	8.3 ± 0.3	0.8 ± 0.1	0.37 ± 0.01	42 ± 1	23 ± 2
Km, μm	4.3 ± 0.4	3.6 ± 0.5	0.64 ± 0.06	0.90 ± 0.15	4.4 ± 0.6	7.7 ± 1.3
kcat/Km, μm−1 min−1	2.4 ± 0.2	2.3 ± 0.3	1.2 ± 0.2	0.41 ± 0.07	9.4 ± 1.3	3.0 ± 0.6

^a From Ref. 36.

^b From the study presented in Table S1.