Showing papers by "Shin-ichi Ayabe published in 1999"

Cloning and Functional Expression of a Cytochrome P450 cDNA Encoding 2-Hydroxyisoflavanone Synthase Involved in Biosynthesis of the Isoflavonoid Skeleton in Licorice

Abstract: Isoflavonoids are distributed predominantly in leguminous plants and play critical roles in plant physiology. A cytochrome P450 (P450), 2-hydroxyisoflavanone synthase, is the key enzyme in their biosynthesis. In cultured licorice (Glycyrrhiza echinata L., Fabaceae) cells, the production of both an isoflavonoid-derived phytoalexin (medicarpin) and a retrochalcone (echinatin) is rapidly induced upon elicitation. In this study, we obtained a full-length P450 cDNA, CYP Ge-8 (CYP93C2), from the cDNA library of elicited G. echinata cells. When the flavanones liquiritigenin and naringenin were incubated with the recombinant yeast microsome expressing CYP93C2, major products emerged and were readily converted to the isoflavones daidzein and genistein by acid treatment. The chemical structures of the products from liquiritigenin (2-hydroxyisoflavanone and isoflavone) were confirmed by mass spectrometry. CYP93C2 was thus shown to encode 2-hydroxyisoflavanone synthase, which catalyzes the hydroxylation associated with 1,2-aryl migration of flavanones. Northern-blot analysis revealed that transcripts of CYP93C2, in addition to those of other P450s involved in phenylpropanoid/flavonoid pathways, transiently accumulate upon elicitation.

Molecular cloning and biochemical characterization of a novel cytochrome P450, flavone synthase II, that catalyzes direct conversion of flavanones to flavones.

Abstract: Cytochrome P450 cDNAs, AFNS2 and TFNS5, were isolated from snapdragon and torenia petal cDNA libraries, respectively, based on the sequence homology with licorice CYP93B1 cDNA encoding (2S)-flavanone 2-hydroxylase. They were expressed in yeast and identified to encode flavone synthase II catalyzing direct conversion of flavanones to flavones probably via 2-hydroxyflavanones.

Induction of Isoflavonoid and Retrochalcone Branches of the Flavonoid Pathway in Cultured Glycyrrhiza echinata Cells Treated with Yeast Extract

Abstract: Yeast extract-treated suspension cultures of a new cell line, AK-1, of Glycyrrhiza echinata were induced to produce an isoflavonoid phytoalexin (medicarpin) and metabolites of retrochalcone/flavone pathway (echinatin, licodione, and 7,4'-dihydroxyflavone). From these cells, putative full-length cDNAs encoding cytochrome P450s, (2S)-flavanone 2-hydroxylase and isoflavone 2'-hydroxylase, were cloned.