N6-(Δ2-Isopentenyl) adenine inhibits the alcohol dehydrogenase activity in cell-free extracts of Zymomonas mobilis

The plant growth substance N⁶-(²-isopentenyl) adenine (i⁶Ade) significantly inhibits the rates of ethanol oxidation and acetaldehyde reduction in vitro by cell-free extracts of Zymomonas mobilis and of an Escherichia coli recombinant strain, containing the Z. mobilis adhB gene. The two-substrate kinetics of ethanol oxidation (forward) is affected by increasing values of dissociation constants for coenzyme and coenzyme —enzyme complexes in the presence of i⁶Ade, whereas the reaction maximum velocity (V _m) remains unchanged and reflects the competitive type of inhibition. Changes of the kinetic constants of acetaldehyde reduction (back) are similar, except the increasing value of V _m and correspond to the CIS (competitive inhibition and stimulation) type of inhibition. The estimated values of inhibition constants of the forward and back reactions are 0.39 ± 0.05 mM and 0.19 ± 0.06 mM, respectively.