TABLE 2.

Substrate specificity of purified 20β-HSDH from B. desmolans

Steroids	Co-substrate	Activity (μmol/min)	Relative Activity (%)
4-pregnen-11β,17,21-triol-20,3-dione	NADH	21 ± 1.4	100
4-pregnen-17,21-diol-3,20-dione	NADH	10.5 ± 1.3	49.8
5β-pregnan-3α,11β,17,21-tetrol-20-one	NADH	10.4 ± 1.7	49.2
4-pregnen-11β,21-diol-3,20-dione	NADH	8.4 ± 1.3	39.8
4-pregnen-11β,17,20β,21-tetrol-3-one	NAD+	0.80 ± 0.02	4.1
4-pregnen-17,20β-diol-3-one	NAD+	0.43 ± 0.03	2.1
4-pregnen-11β,20β,21-triol-3-one	NAD+	NA	NA
4-pregnen-11β,17,20α,21-tetrol-3-one	NAD+	NA	NA
4-pregnen-17,20α-diol-3-one	NAD+	NA	NA

The reactions were initiated by addition of 50 nM purified enzyme to 0.5 ml of 0.05 M sodium phosphate buffer (pH 7) containing 0.15 M NaCl, 20% glycerol, 0.01 M 2-mercaptoethanol, 50 μM steroid, and 150 μM NAD(H) at 37°C. All values are the means of four replicates. NA, no activity.