title: Anthocyanidin reductases from Medicago truncatula and Arabidopsis thaliana.
abstract: Anthocyanidin reductase (ANR), encoded by the BANYULS gene, is a newly discovered enzyme of the flavonoid pathway involved in the biosynthesis of condensed tannins. ANR functions immediately downstream of anthocyanidin synthase to convert anthocyanidins into the corresponding 2,3-cis-flavan-3-ols. We report the biochemical properties of ANRs from the model legume Medicago truncatula (MtANR) and the model crucifer Arabidopsis thaliana (AtANR). Both enzymes have high temperature optima. MtANR uses both NADPH and NADH as reductant with slight preference for NADPH over NADH. In contrast, AtANR only uses NADPH and exhibits positive cooperativity for the co-substrate. MtANR shows preference for potential anthocyanidin substrates in the order cyanidin>pelargonidin>delphinidin, with typical Michaelis-Menten kinetics for each substrate. In contrast, AtANR exhibits the reverse preference, with substrate inhibition at high concentrations of cyanidin and pelargonidin. (+)-Catechin and (+/-)-dihydroquercetin inhibit AtANR but not MtANR, whereas quercetin inhibits both enzymes. Possible catalytic reaction sequences for ANRs are discussed.
authors.affiliation: Plant Biology Division, Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401, USA.
authors.forename: De-Yu
authors.initials: DY
authors.lastname: Xie
authors.forename: Shashi B
authors.initials: SB
authors.lastname: Sharma
authors.forename: Richard A
authors.initials: RA
authors.lastname: Dixon
mesh_terms: D000595:Amino Acid Sequence; D000872:Anthocyanins / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology*; D005419:Flavonoids / Q000096:biosynthesis / Q000737:chemistry / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D029902:Medicago / Q000201:enzymology*; D008969:Molecular Sequence Data; D009243:NAD / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D013634:Tannins / Q000096:biosynthesis; D013696:Temperature
chemical_list: D000872:Anthocyanins; D005419:Flavonoids; D011993:Recombinant Fusion Proteins; D013634:Tannins; D009243:NAD; C404987:flavan-3-ol; D009249:NADP; D009247:NADH, NADPH Oxidoreductases