. Author manuscript; available in PMC: 2010 Mar 25.

Published in final edited form as: Mol Cell Endocrinol. 2008 Oct 8;301(1-2):174–182. doi: 10.1016/j.mce.2008.09.029

Table 3.

Substrate kinetics for the 3β-HSD and isomerase activities for purified human P195R-2, 3β-HSD1 and 3β-HSD2.

	3β-HSD¹			Isomerase²
Purified Enzyme	K_m μM	k_cat min⁻¹	k_cat/K_m min⁻¹ μM⁻¹	K_m μM	k_cat min⁻¹	k_cat/K_m min⁻¹ uM⁻¹
P195R-2	13.3 ± 2.5	9.5 ± 0.7	0.71 ± 0.05	119 ± 5.0	131 ± 9.8	1.10 ± 0.09
3β-HSD1	3.7 ± 0.2	3.3 ± 0.2	0.89 ± 0.04	27.9 ± 1.1	50.2 ± 2.0	1.80 ± 0.08
3β-HSD2	47.3 ± 2.9	6.9 ± 0.5	0.15 ± 0.01	88.4 ± 5.7	81.4 ± 6.0	0.92 ± 0.06

Kinetic constants for the 3β-HSD substrate were determined in incubations containing DHEA, NAD⁺ and purified enzyme in 0.02 M potassium phosphate, pH 7.4, as described in Experimental Procedures.

Kinetic constants for the isomerase substrate were determined in incubations of 5-androstene-3,17-dione, NADH and purified enzyme in 0.02 M potassium phosphate buffer, pH 7.4, as described in Experimental Procedures. All values are the means of triplicate determinations ± standard deviations.