Table 1.

Rate constants determined from transient single turnover experiments.

Parametersa	A1/Atotal (s−1)	kobs1 (s−1)	kobs2 (s−1)	kcat (s−1)d
Fast substrates – biphasic progress curves
aldosterone	0.47	1.27 ± 0.02	0.128 ± 0.002	0.15 ± 0.01
cortisoneb	0.32	0.78 ± 0.01	0.0943 ± 0.0004	0.195 ± 0.002
testosterone	0.27	0.32 ± 0.01	0.0704 ± 0.0009	0.14 ± 0.03
corticosterone	0.30	0.119 ± 0.003	0.0176 ± 0.0002	0.032 ± 0.002
Slow substrates – monophasic progress curves
7α-hydroxycholestenonec	NA	0.00523 ± 0.00001	NA	0.033 ± 0.002
cholestenone	NA	0.00133 ± 0.00001	NA	0.0100 ± 0.0007

^aSingle turnover experiments were performed at 37 °C in 100 mM potassium phosphate buffer (pH 7.0), containing 4% acetonitrile as cosolvent.

^bFor cortisone reduction at pH 6, k_obs1 = 1.69 s⁻¹, k_obs2 = 0.21 s⁻¹[9].

^cFor 7α-hydroxycholestenone reduction at pH 6, k_obs1 = 0.021 s⁻¹ [9].

^dk_cat was determined at 100 mM potassium phosphate buffer (pH 6.0) [8].