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