Cross-linked crystals of hydroxynitrile lyase as catalyst for the synthesis of optically active cyanohydrins

Purified hydroxynitrile lyase (HNL) from Manihot esculenta was crystallized by the sitting-drop vapour-diffusion method. The bipyramidal crystals formed (10-20 mum) were cross-linked with different amounts of glutaraldehyde and used as biocatalyst for the synthesis of optically active cyanohydrins. The cross-linked crystals were more stable than Celite-immobilized enzymes when incubated in organic solvents, especially in polar solvents. After six consecutive batch reactions in dibutylether, the remaining activity of the cross-linked crystals was more than 70 times higher than for the immobilized enzymes. Nevertheless, the specific activity of the cross-linked crystals (per milligram protein) was reduced compared to the activity of immobilized enzymes. The product enantiopurity was independent of the type of enzyme preparation used. (C) 2001 Elsevier Science B.V. All rights reserved.