CARBONYL REDUCTASE-ACTIVITY EXHIBITED BY PIG TESTICULAR 20-BETA-HYDROXYSTEROID DEHYDROGENASE

The carbonyl reductase activity exhibited by pig testicular 20 beta-hy droxysteroid dehydrogenase (20 beta-HSD) was examined using a recombin ant enzyme. Kinetic parameters mere obtained for 48 carbonyl group-con taining substrates, including aromatic aldehydes, aromatic ketones, cy cloketones, quinones, aliphatic aldehydes and aliphatic ketones. 20 be ta-HSD showed a high affinity towards quinones, such as 9,10-phenanthr enequinone, alpha-naphthoquinone and menadione (K-m values of 4, 2 and 5 mu M, respectively), and the substrate utilization efficiency (V-ma x/K-m) of the enzyme against these quinones was very high. Cyclohexano ne and 2-methylcyclohexanone were also reduced with a high V-max/K-m v alue, but not cyclopentanone or 2-methylcyclopentanone. Various aromat ic aldehydes and ketones including benzaldehyde-and acetophenone-deriv atives were reduced by 20 beta-HSD. Especially, 4-nitrobenzaldehyde an d 4-nitroacetophenone were reduced with high V-max/K-m values in the r elated compounds. The enzyme also reduced the pyridine-derivatives, 2- , 3-, and 4-benzoylpyridine, with the V-max/K-m value for 2-benzoylpyr idine being the highest. 20 beta-HSD reduced aliphatic aldehydes and a liphatic ketones, but was more effective on the former. The correlatio n between the structure of carbonyl compounds and their substrate V-ma x/K-m is discussed.