|Georg G. Gross
The biosynthesis of hydrolyzable tannins (i.e. gallotannins and ellagitannins) was studied with enzyme preparations from Quercus robur, Q. rubra, Rhus typhina and Tellima grandiflora. The primary metabolite -glucogallin (1-O--D-glucose), formed from free gallic acid and UDP-glucose, was also found to serve as the principal acyl donor in the subsequent step-wise conversion of this mono-ester to 1,2,3,4,6-penta-O-galloyl--D-glucose, the common precursor of both gallotannins and ellagitannins.
Gallotannins were formed by the continuation of this reaction principle, while ellagitannins were synthesized by oxidation of pentagalloylglucose in the presence of a novel FMN-dependent enzyme.
In addition, also counter-directed catabolic processes appear to occur in higher plants as indicated by the discovery of a tannase-like hydrolase.
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