The enzyme, characterized from Vitis vinifera (grape), participates in the flavonoid biosynthesis pathway. It catalyses the double reduction of anthocyanidins, producing a mixture of (2S,3S)- and (2S,3R)-flavan-3-ols. The enzyme catalyses sequential hydride transfers to C-2 and C-4, respectively. Epimerization at C-3 is achieved by tautomerization that occurs between the two hydride transfers. cf. EC 1.3.1.77, anthocyanidin reductase [(2R,3R)-flavan-3-ol-forming].
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The enzyme appears in viruses and cellular organisms
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SYSTEMATIC NAME
IUBMB Comments
(2S)-flavan-3-ol:NAD(P)+ oxidoreductase
The enzyme, characterized from Vitis vinifera (grape), participates in the flavonoid biosynthesis pathway. It catalyses the double reduction of anthocyanidins, producing a mixture of (2S,3S)- and (2S,3R)-flavan-3-ols. The enzyme catalyses sequential hydride transfers to C-2 and C-4, respectively. Epimerization at C-3 is achieved by tautomerization that occurs between the two hydride transfers. cf. EC 1.3.1.77, anthocyanidin reductase [(2R,3R)-flavan-3-ol-forming].
ANR is strictly pro-S stereospecific and the reaction mechanism involves two hydride transfers from two distinct NADPH molecules. ANR produces a 50:50 mixture of 2,3-cis and 2,3-trans flavan-3-ols, i.e. 2S,3S- and 2S,3R-flavan-3-ols
hyperbolic and rapid-equilibrium ordered mechanism, with NADPH binding first. The most likely mechanism is sequential ordered Bi Uni Uni Bi, with NADPH binding first and NADP+ released last, and internal conversion of the first ternary complex, i.e. that associated with the first hydride transfer, is rate-limiting
in the presence of excess NADP+, ANR acts as a flavan-3-ol C3-epimerase, but only with 2R-flavan-3-ols, not with 2S-flavan-3-ols produced by the enzyme in the forward reaction. C3-epimerization should be achieved by tautomerization between the two hydride transfers and this produces a quinone methide intermediate which serves as C4 target of the second hydride transfer, avoiding any stereospecific modification of carbon 3. The inversion of C2 stereochemistry required for reverse epimerization suggests that the 2S configuration induces an irreversible product dissociation
hyperbolic binding of NADPH and NADP+ to the free enzyme, with a single binding site each and with dissociation constants of 0.046 mM for NADPH and 0.083 for NADP+
hyperbolic binding of NADPH and NADP+ to the free enzyme, with a single binding site each and with dissociation constants of 0.046 mM for NADPH and 0.083 for NADP+
grape flowers have high levels of proanthocyanidins, and accumulation continues in skin and seeds from fruit set until the onset of ripening. ANR is expressed throughout early flower and berry development, with expression increasing after fertilization. During grape ripening, proanthocyanidin levels decrease in both skin and seeds, and expression of genes encoding ANR and LAR are no longer detected
a high amount of leucoanthocyanidin reductases LAR1 and LAR2 and of ANR is present at the pre-veraison stage, localized on the outer layer of the berry skin, the vascular bundle and the inner layer of the seed coat
grape flowers have high levels of proanthocyanidins, and accumulation continues in skin and seeds from fruit set until the onset of ripening. ANR is expressed throughout early flower and berry development, with expression increasing after fertilization. During grape ripening, proanthocyanidin levels decrease in both skin and seeds, and expression of genes encoding ANR and LAR are no longer detected
mRNA accumulates at the early stage of berry development and decreases toward the ripening stage. Proanthocyanidins accumulate in the berry skins and seeds before veraison, especially during the early stages of development
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CRYSTALLIZATION (Commentary)
ORGANISM
UNIPROT
LITERATURE
to 2.2 A resolution. The active site is wide open with the side chains of the catalytic residues Tyr168 and Lys172 turned away from the nucleotide-binding site
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EXPRESSION
ORGANISM
UNIPROT
LITERATURE
trreatment with abscisic acid affects tannin content and is involved in the tannin biosynthesis pathway in grape skin by decreasing leucoanthocyanidin reductase and ANR activity and repressing the expression of related genes a few days after application
Proanthocyanidin synthesis and expression of genes encoding leucoanthocyanidin reductase and anthocyanidin reductase in developing grape berries and grapevine leaves
Biosynthesis of flavan 3-ols by leucoanthocyanidin 4-reductases and anthocyanidin reductases in leaves of grape (Vitis vinifera L.), apple (Malus x domestica Borkh.) and other crops
Involvement of abscisic acid in controlling the proanthocyanidin biosynthesis pathway in grape skin: new elements regarding the regulation of tannin composition and leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR) activities and expres