Biosynthesis of flavan-3-ols by leaf extracts of Onobrychis viciifolia
1997
Singh, S. | McCallum, J. | Gruber, M.Y. | Towers, G.H.N. | Muir, A.D. | Bohm, B.A. | Koupai-Abyazani, M.R. | Glass, A.D.M.
A subcellular enzyme fraction (Mr > 20 X 10(6) from immature sainfoin leaves catalysed the two-step NADPH-dependent reduction of (+)-dihydromyricetin to (+)-gallocatechin. No enzyme-mediated (-)-epigallocatechin was formed under the conditions employed, and only traces of 2R,3S-trans-3S,4S-cis-leucodelphinidin were observed. The two-step reductase activity mirrored proanthocyanidin content, rising to a maximum before leaflet unfolding, then declining during leaf expansion. When [14C](+)-dihydromyricetin and [C4-3H]2R,3S-trans-3S,4S-cis-leucodelphinidin were supplied to the same fraction, preferential utilization of (+)-dihydromyricetin was observed. Enzymic formation of proanthocyanidin dimers could not be detected using these preparations under a variety of conditions. However, a small portion of radioactivity was bound to the subcellular fraction after addition of labelled (+)-catechin. In addition, in vivo incorporation of (+)-dihydromyricetin into proanthocyanidins was observed.
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