. Author manuscript; available in PMC: 2009 Jul 1.

Published in final edited form as: J Steroid Biochem Mol Biol. 2008 May 3;111(1-2):66–73. doi: 10.1016/j.jsbmb.2008.04.007

Table 1.

Comparison of inhibition constants of trilostane and 4α,5α-epoxy-testosterone for purified human 3β-HSD1, 3β-HSD2, M187T and S124T.

	Inhibitor steroid K_i (µM)¹
Enzyme	trilostane	4α,5α-epoxy-testosterone
3β-HSD1	0.10 ± 0.01 (C)	4.08 ± 0.26
3β-HSD2	1.60 ± 0.10	3.75 ± 0.31 (C)
M187T	0.83 ± 0.06	2.80 ± 0.19 (C)
S124T	0.41 ± 0.03	4.34 ± 0.32 (C)

For 3β-HSD1, the incubations at 27 °C contained sub-saturating concentrations of DHEA (4.0 µM or 8.0 µM), NAD⁺ (0.2 mM), purified human type 1 enzyme (0.03–0.04 mg) and trilostane (0–0.75 µM) or 4α,5α-epoxy-testosterone (0–10.0 µM) in 0.02 M potassium phosphate buffer, pH 7.4. For 3β-HSD2, DHEA (15.0 µM or 40.0 µM) and trilostane (0–7.5 µM) or 4α,5α-epoxy-testosterone (0–10.0 µM). For S124T, DHEA (15.0 µM or 40.0 µM) and trilostane (0–1.0 µM) or 4α,5α-epoxy-testosterone (0–17.5 µM). For M187T, DHEA (8.0 µM or 20.0 µM) and trilostane (0–5.0 µM) or 4α,5α-epoxy-testosterone (0–12.5 µM). Dixon analysis (I versus 1/V) was used to determine the type of inhibition and calculate the K_i values. K_i values are means of triplicate determinations ± standard deviations. (C) denotes a competitive mode of inhibition, and no notation indicates a non-competitive mode.