The Use of Lewis Cell to Investigate the Enzyme Kinetics of an (S)-Hydroxynitrile Lyase in Two-Phase Systems
Michael Bauer1, Roland Geyer1, Herfried Griengl2 and Walter Steiner1*
1Institute of Biotechnology, Enzyme-Technology Group, SFB Biocatalysis Graz University of Technology, Petersgasse 12, A-8010 Graz, Austria
2Institute of Organic Chemistry, SFB Biocatalysis Graz University of Technology, Stremayrgasse 16, A-8010 Graz, Austria
Article history:
Received June 29, 2001
Accepted November 8, 2001
Key words:
Lewis cell, two-phase system, mass transfer, enzyme kinetics, hydroxynitrile lyase, Hevea brasiliensis
Summary:
(S)-Hydroxynitrile lyase from Hevea brasiliensis (HbHnl) (EC 4.1.2.39) catalyzes the reversible synthesis of chiral cyanohydrins from aldehydes or ketones and HCN. The enzymatic formation of (S)-mandelonitrile (MN) from benzaldehyde (BA) and HCN was studied in two-phase systems of buffer and organic solvents (diisopropyl ether, methyl-t-butyl ether) using a Lewis cell to investigate the interaction between mass transfer and the biocatalytic reaction. The enzymatic reaction rate in the aqueous phase saturated with organic solvents is drastically reduced in comparison to pure buffer due to the increase of the Michaelis- Menten constants of the substrates. Mass transfer of the substrates from the organic to the aqueous phase and mass transfer of the product in the opposite direction could be described by the two-film theory. The formation of (S)-mandelonitrile in the Lewis cell follows an aqueous phase distributed reaction model, which means that the enzymatic reaction takes place in the bulk of the aqueous phase and in the thin film close to the interface and/or directly at the interface. Using the Hatta number it could be shown that the mass transfer of benzaldehyde from the organic to the aqueous phase is enhanced by the biocatalytic reaction of the (S)-hydroxynitrile lyase from Hevea brasiliensis.
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