Kinetic studies of the asymmetric Henry reaction catalyzed by hydroxynitrile lyase from Hevea brasiliensis

The asymmetric Henry reaction catalyzed by hydroxynitrile lyase from Hevea brasiliensis is an example of enzymatic catalytic promiscuity. It could be an attractive method to produce optically active beta-nitroalcohols, but unfortunately the enzyme has very low activity in this unnatural reaction. To get an insight into the reaction mechanism, the enzyme kinetics of this promiscuous biotransformation were studied using the cleavage and synthesis of 2-nitro-1-phenylethanol as a model system. The results indicate that the kinetic behavior of the enzyme in the Henry reaction fits the classical Rapid Equilibrium Random Bi Uni/Uni Bi mechanistic model with independent substrate binding. The measured kinetic parameters imply that the bottleneck for this biotransformation is the very low turnover number of the enzyme, not the binding of the substrates.