title: Purification and Characterization of a Novel (R)-Mandelonitrile Lyase from the Fern Phlebodium aureum.
abstract: 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.
authors.affiliation: 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.
authors.forename: H.
authors.initials: H
authors.lastname: Wajant
authors.forename: S.
authors.initials: S
authors.lastname: Forster
authors.forename: D.
authors.initials: D
authors.lastname: Selmar
authors.forename: F.
authors.initials: F
authors.lastname: Effenberger
authors.forename: K.
authors.initials: K
authors.lastname: Pfizenmaier