Table 1

Substrate reactivity of hST1B2

SubstrateActivity[Substrate]
nmol/min/mg % μm
3,3′,5-T31.1110050
3,3′,5,5′-T40.055200
3,3′,5′-rT30.6761200
3,3′-T218.91628150
3,5-T20.011200
1-Naphthol74.4670510
4-Nitrophenol11.41030100
Diethylstilbestrol0.8274100
E2N.D.1–25
E1N.D.1–25
DHEAN.D.1–25
CortisolN.D.1–25
PregnenoloneN.D.1–25
TestosteroneN.D.1–25
DihydroequileninN.D.1–25

hST1B2 was expressed in E. coli, partially purified by DEAE-Sepharose Cl-6B chromatography (Falany et al., 1994), and used to assay the ability of the enzyme to sulfate a number of possible substrates. Because substrate inhibition is a characteristic of the STs (Falany, 1997), each substrate was assayed using a range of concentrations to determine the concentration generating maximal activity. The steroids were tested as substrates at several concentrations from 1 to 25 μm. The reaction rates for each substrate then were compared using the concentration generating maximal activity. The activity of hST1B2 with 3,3′,5-T3 is chosen as 100%.

• N.D., no detectable activity.