A correlation was observed between the values of specificity constant (kcat/Km) of carbonyl reductase from rabbit liver for acetohexamide analogs and their partition coefficients. This result indicates that the hydrophobicity in straight-chain alkyl groups of acetohexamide analogs plays an important role in the catalytic activity and substrate-binding capacity of the enzyme. Furthermore, the double logarithmic plots of kcat/Km values of the enzyme for 4-acetylpyridine analogs with a straight-chain alkyl group up to five carbon atoms against their partition coefficients gave a straight line. On the other hand, the plots for 4-acetylpyridine analogs with a straight-chain alkyl group over five carbon atoms and with a branched-chain alkyl group were away from the straight line. It is reasonable to postulate that a hydrophobic pocket is located in the substrate-binding domain of the enzyme.
