Catabolism of (R)-Amygdalin and (R)-Vicianin by Partially Purified ß-Glycosidases from Prunus serotina Ehrh. and Davallia trichomanoides

Abstract

Mature black cherry(Prunus serotina Ehrh.)seeds accum ulate high levels of the cyanogenic disaccharide (R)-amygdalin. Extracts from these seeds contain two R-glycosidases which been identified and completely resolved by DEAE-cellulose ion-exchange chromatography.Amygdalin hydrolase hydrolyzed (ß)-am ygdalin atanoptimum pH of 5.5, releasing (ß)-prunasin and D-glucose.This enzyme showed highest activity towards (R)-am ygdalin and failed hydrolyze(R)-prunasin.linamarin, R-gentiobiose and cellobiose.A distinct R-prunasin hydrolase, displayed a pronounced preference for(R)-prunasin, hydrolyzing cyanogenic monosaccharide atan optimum pH of6.5 to mandelonitrile and D-glucose. hydrolase was inactive towards(R)-am ygdalin, linamarin, and R-gentiobiose.Both showed significant activity towards the artificial substrates R-ONPGlu and R-PNPGlu but not hydrolyzex-PNPGlu.In view of the pronounced specificity of these enzymestowards endogenous cyanogens, it is concluded that upon disruption of black cherry amygdalin is catabolized to mandelonitrile in a stepwise manner (the sequentialmechanism)amygdalin hydrolase and prunasin hydrolase with (Ä)-prunasinserving as intermediate.Youngfronds of Davallia trichomanoides are rich sources of (R)-vicianin (the R-vicianoside of (R)-mandelonitrile).AR-glycosidase, vicianin hydrolase, has been partially purified from extracts by ion-exchangechromatography.At the optim um pH of 6.0, this enzyme highest hydrolytic activity with(R)-vicianin, although both(R)-amygdalinand (R)-could be hydrolyzed at approximately 15% of the rate observed with(R)-vicianin.It failed hydrolyze/i-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 mandelonitrileand the respective disaccharides vicianose and R-gentiobiose. © 1984, Walter de Gruyter. All rights reserved.