Plant Physiol.
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PLANT PHYSIOLOGY , Vol 109, Issue 4 1231-1238, Copyright © 1995 by American Society of Plant Biologists

BIOCHEMISTRY AND ENZYMOLOGY

Purification and Characterization of a Novel (R)-Mandelonitrile Lyase from the Fern Phlebodium aureum

H. Wajant, S. Forster, D. Selmar, F. Effenberger and K. Pfizenmaier
Institut fur Zellbiologie und Immunologie der Universitat Stuttgart, Allmandring 31 (H.W., K.P.), and Institut fur Organische Chemie der Universitat Stuttgart, Pfaffenwaldring 55 (S.F., F.E.), 70569 Stuttgart, Germany

Using high-performance liquid chromatography and nuclear magnetic resonance we identified vicianin as the cyanogenic compound of Phlebodium aureum. The (R)-hydroxynitrile lyase involved during cyanogenesis in the catabolism of the aglycon ([R]-mandelonitrile) was purified to apparent homogeneity. The purified holoenzyme is a homomultimer with subunits of Mr = 20,000. At least three isoforms of the enzyme exist. In contrast to other hydroxynitrile lyases, mandelonitrile lyase (MDL) from P. aureum was not inhibited by sulfhydryl- or hydroxyl-modifying reagents, suggesting a different catalytic mechanism. The enzyme is active over a broad temperature range, with maximum activity between 35 and 50[deg]C, and a pH optimum at 6.5. In contrast to (R)-MDLs isolated from several species of the Rosaceae family, (R)-MDL from P. aureum is not a flavoprotein. The substrate specificity was investigated using immobilized enzyme and diisopropyl ether as solvent. The addition of cyanide to aromatic and heterocyclic carbonyls is catalyzed by this (R)-MDL, whereas aliphatic carbonyls are poorly converted.




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Copyright © 1995 by the American Society of Plant Biologists