Kinetic properties of 7α-hydroxysteroid dehydrogenase from Escherichia coli 080

Abstract

Results on the kinetics of 7α-hydroxysteroid dehydrogenase 7α-HSDH showed that this enzyme could oxidize all bile acids having an –OH group at the C-7 position. Lineweaver-Burk plots showed Michaelis constant (Km) values of 0.83 and 0.12 mM for cholic acid and chenodeoxycholic acid, respectively. The effect of enzyme concentration on the reaction velocity showed a constant increase in the enzyme activity with increase in enzyme-protein concentration. 7α-HSDH was activated by Na+, K+, Ca2+, and Mn2+ ions and by reducing agents having a thiol group (dithiothreitol, 2-mercaptoethanol). Co2+, Hg2+, Fe3+, Mg2+, Zn2+, Ba2+, and Cu2+ ions, chelating agents (potassium oxalate, heparin, EDTA), oxidizing agents (sodium perchlorate, sodium periodate, sodium persulphate), and detergents (Tween 20, Tween 40, Tween 80, Triton X-100, sodium lauryl sulphate) were inhibitory to 7α-HSDH activity.Key words: 7α-hydroxysteroid dehydrogenase, bile acids, NAD+, Escherichia coli 080, enzyme kinetics.