Purification and characterization of acetone cyanohydrin lyase from Linum usitatissimum

The hydroxynitrile lyase (EC 4.1.2.--) which catalyzes the dissociation of the cyanohydrins of acetone and 2-butanone has been isolated and purified from young seedlings of flax (Linum usitatissimum L.). The purification procedure involved precipitation with (NH4)2SO4, chromatofocusing, and chromatography on DEAE-cellulose, hydroxylapatite, Sephacryl 200, and Matrex Red A gel columns with a final recovery of 21%. Purification of 136-fold yielded an apparently homogeneous preparation that, in contrast to the lyases isolated from Prunus species, is not a flavoprotein. The subunit molecular weight of 42,000 was estimated by gel electrophoresis in the presence of sodium dodecyl sulfate. The native molecular weight of the enzyme was estimated by gel filtration (HPLC) to be 82,000. The enzyme has a narrow pH optimum around 5.5 and is highly stable at 4 degrees C.