Function
Produces the terminal flavan-3-ol monomers required for the formation of proanthocyanidins or condensed tannins in leaves and flowers, as well as in the skin and seeds of developing berries (Ref.1, PubMed:16169968). Behaves as a reductase and as a C-3 epimerase (PubMed:20030585). Catalyzes the double reduction of anthocyanidins, producing a mixture of (2S,3S)- and (2S,3R)-flavan-3-ols (Ref.1). The enzyme catalyzes sequential hydride transfers to C-2 and C-4, respectively and epimerization at C-3 is achieved by tautomerization that occurs between the two hydride transfers (PubMed:20030585). Converts cyanidin, pelargonidin and delphinidin into catechin and epicatechin, afzelechin and epiafzelechin, and gallocatechin and epigallocatechin respectively (PubMed:19690377).
Sequence
MATQHPIGKKTACVVGGTGFVASLLVKLLLQKGYAVNTTVRDPDNQKKVSHLLELQELGDLKIFRADLTDELSFEAPIAGCDFVFHVATPVHFASEDPENDMIKPAIQGVVNVMKACTRAKSVKRVILTSSAAAVTINQLDGTGLVVDEKNWTDIEFLTSAKPPTWGYPASKTLAEKAAWKFAEENNIDLITVIPTLMAGSSLTSDVPSSIGLAMSLITGNEFLINGMKGMQMLSGSVSIAHVEDVCRAHIFVAEKESASGRYICCAANTSVPELAKFLSKRYPQYKVPTDFGDFPPKSKLIISSEKLVKEGFSFKYGIEEIYDESVEYFKAKGLLQN