Degradation of the pterocarpan phytoalexin medicarpin by Ascochyta rabiei

Transformações Enzimáticas De Flavonóides

“…No entanto, essas transformações podem levar à formação de compostos intermediários na seqüência metabólica passíveis de serem modificados posteriormente a outros fragmentos. Alguns exemplos dessas transformações são a desmetilação da 6a-hidroxipterocarpana pisatina por Nectria haematococca (VAN-ETTEN, MATTHEWS e MATTHEWS, 1989), a desmetilação de medicarpina por Ascochyta rabiei (KRAFT et al, 1987), e a desmetilação de biocanina a genisteína por Fusarium solani f. sp. phaseoli, com redução de duas isoflavonas (TURBEK et al, 1990).…”

Partial Characterization of an Enzyme from the Fungus Ascochyta rabiei for the Reductive Cleavage of Pterocarpan Phytoalexins to 2′-Hydroxyisoflavans

“…Mycelium was grown and har vested as described [8,10]. Incubation experiments of mycelium with pterocarpans have also been reported [8,9],…”

“…The isolation of phenolic compounds from incu bation assays and their determ ination by HPLC followed our earlier reports [8,10] A fter 165 ml had been eluted a linear gradient of 0.1 m NaCl in the same phosphate buffer was ap plied. Oxidoreductase activity appeared in the frac tions 14-22 whereas the oxidizing enzyme activity catalyzing the formation of compounds 5 and 6 ( Fig.…”

“…In the course of our studies on the fungal degrada tion of pterocarpan phytoalexins by fungi of the genus Fusarium [6,7] and by the chickpea (Cicer arietinum L.) pathogen A scochyta rabiei [8][9][10] we have dem onstrated the conversion of m edicarpin, 1 and maackiain, 2 ( Fig. 1) to 7,2'-dihydroxy-4'-m ethoxyisoflavan, 3, and 7,2'-dihydroxy-4',5'-m ethylenedioxyisoflavan, 4, respectively.…”

“…1) to 7,2'-dihydroxy-4'-m ethoxyisoflavan, 3, and 7,2'-dihydroxy-4',5'-m ethylenedioxyisoflavan, 4, respectively. The cleavage of a pterocarpan to the corresponding 2'-hydroxyisoflavan has repeatedly been shown as an initial step in the fungal degradation of pterocarpan phytoalexins [1,6,[7][8][9]11]. Alternative routes for pterocarpan catabolism by fungi are the form ation of a la-hydroxy-pterocarp-l,4-diene-3-one such as 5 or 6 [12,13], a 2'-hydroxyisoflavanone [12,13] or an 0-demethylation product [1,4,6],…”