Stability and stabilization of hydroxynitrile lyase in organic solvents

The stability of hydroxynitrile lyase from Hevea brasiliensis has been studied in organic solvents. In dry solvents, the enzyme had half-lives in the range 1400-2500 hours. The enzyme half-life was one order of magnitude lower if the medium was water saturated. The substrates, aldehyde and hydrogen cyanide, were found to promote enzyme deactivation. The deactivation increased with substrate concentration, but was reduced in hydrophilic solvent. At high substrate concentration (2 M) in tert-butyl methyl ether, the enzyme half-life was 1.7 h when incubated with hydrogen cyanide while it was 1.0 h with 3-phenylpropionaldehyde. The addition of polyethylenimine, 125 mg per g of enzyme preparation, increased the enzyme half-life to 110 h when incubated with hydrogen cyanide and to 3.2 h with 3-phenylpropanaldehyde in tert-butyl methyl ether. Albumin and poly(ethylene glycol) gave similar stabilization effect.