Catabolism of (R)-Amygdalin and (R)-Vicianin by Partially Purified ß-Glycosidases from Prunus serotina Ehrh. and Davallia trichomanoides
| Autor: | Pauline A. Lizotte, Jonathan E. Poulton, Gary W. Kuroki |
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| Rok vydání: | 1984 |
| Předmět: | |
| Zdroj: | Zeitschrift für Naturforschung C. 39:232-239 |
| ISSN: | 1865-7125 0939-5075 |
| DOI: | 10.1515/znc-1984-3-405 |
| Popis: | Mature black cherry (Prunus serotina Ehrh.) seeds accum ulate high levels of the cyanogenic disaccharide (R)-amygdalin. Extracts from these seeds contain two β-glycosidases which have been identified and completely resolved by DEAE-cellulose ion-exchange chromatography. Amygdalin hydrolase hydrolyzed (R)-am ygdalin at an optimum pH of 5.5, releasing (R)-prunasin and D-glucose. This enzyme showed highest activity towards (R)-am ygdalin and failed to hydrolyze (R)-prunasin. linamarin, β-gentiobiose and cellobiose. A distinct β-glycosidase, prunasin hydrolase, displayed a pronounced preference for (R)-prunasin, hydrolyzing this cyanogenic monosaccharide at an optimum pH of 6.5 to mandelonitrile and D-glucose. Prunasin hydrolase was inactive towards (R)-am ygdalin, linamarin, and β-gentiobiose. Both enzymes showed significant activity towards the artificial substrates β-ONPGlu and β-PNPGlu but did not hydrolyze α-PNPGlu. In view of the pronounced specificity of these enzymes towards endogenous cyanogens, it is concluded that upon disruption of black cherry seeds (R)- amygdalin is catabolized to mandelonitrile in a stepwise manner (the sequential mechanism) by amygdalin hydrolase and prunasin hydrolase with (R)-prunasin serving as intermediate. Young fronds of Davallia trichomanoides are rich sources of (R)-vicianin (the β-vicianoside of (R)-mandelonitrile). A β-glycosidase, vicianin hydrolase, has been partially purified from frond extracts by ion-exchange chromatography. At the optimum pH of 6.0, this enzyme showed highest hydrolytic activity with (R)-vicianin, although both (R)-am ygdalin and (R)-prunasin could be hydrolyzed at approximately 15% of the rate observed with (R)-vicianin. It failed to hydrolyze β-gentiobiose, cellobiose, linamarin and α-PNPGlu. Closer exam ination revealed that (R)-vicianin and (R)-amygdalin were hydrolyzed at the aglycone-disaccharide bond (the simultaneous mechanism) yielding mandelonitrile and the respective disaccharides vicianose and β-gentiobiose |
| Databáze: | OpenAIRE |
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