KINETIC-STUDIES ON THE REDUCTION OF ACETOHEXAMIDE CATALYZED BY CARBONYL REDUCTASE FROM RABBIT KIDNEY

The kinetic mechanism for the reduction of acetohexamide catalyzed by carbonyl reductase from rabbit kidney was investigated. The initial ve locity and product inhibition studies indicated that the enzymatic rea ction follows an ordered Bi Bi mechanism, in which NADPH binds to the enzyme first and NADP leaves last. This kinetic mechanism was confirme d on the basis of the dead-end inhibition by Cibacron Blue and the bin ding of NADPH and NADP to the free enzyme. However, whether or not coe nzyme-induced isomerization is involved in the enzymatic reaction rema ins to be clarified. In kinetic studies of inhibition of the enzyme by therapeutically active drugs, indomethacin and befunolol were found t o be noncompetitive and competitive inhibitors, respectively, with res pect to acetohexamide.