摘要：The carbonyl reductase activity exhibited by pig testicular 20β-hydroxysteroid dehydrogenase (20β-HSD) was examined using a recombinant enzyme. Kinetic parameters were obtained for 48 carbonyl group-containing substrates, including aromatic aldehydes, aromatic ketones, cycloketones, quinones, aliphatic aldehydes and aliphatic ketones. 20β-HSD showed a high affinity towards quinones, such as 9, 10-phenanthrenequinone, α-naphthoquinone and menadione (Km values of 4, 2 and 5 μM, respectively), and the substrate utilization efficiency (Vmax/Km) of the enzyme against these quinones was very high. Cyclohexanone and 2-methylcyclohexanone were also reduced with a high Vmax/Km value, but not cyclopentanone or 2-methylcyclopentanone. Various aromatic aldehydes and ketones including benzaldehyde- and acetophenone-derivatives were reduced by 20β-HSD. Especially, 4-nitrobenzaldehyde and 4-nitroacetophenone were reduced with high Vmax/Km values in related compounds. The enzyme also reduced the pyridine-derivatives, 2-, 3-, and 4-benzoylpyridine, with the Vmax/Km value for 2-benzoylpyridine being the highest. 20β-HSD reduced aliphatic aldehydes and aliphatic ketones, but was more effective on the former. The correlation between the structure of carbonyl compounds and their substrate Vmax/Km is discussed.
