Degradation of quercetin and luteolin by Eubacterium ramulus

The degradation of the flavonol quercetin and the flavone lutcolin by Eubac terium ramulus, a strict anaerobe of the human intestinal tract, was studie d. Resting cells converted these flavonoids to 3,4-dihydroxyphenylacetic ac id and 3-(3,4-dihydroxphenyl)propionic acid, respectively. The conversion o f quercetin was accompanied by the transient formation of two intermediates , one of which was identified as taxifolin based on its specific retention time and UV and mass spectra. The structure of the second intermediate, alp hitonin, was additionally elucidated by H-1 and C-13 nuclear magnetic reson ance analysis. In resting-cell experiments, taxifolin in turn was converted via alphitonin to 3,4-dihydroxylihenylacetic acid. Alphitonin, which was p repared by enzymatic conversion of taxifolin and subsequent purification, w as also transformed to 3,4-dihydroxyphenylacetic acid. The coenzyme-indepen dent isomerization of taxifolin to alphitonin was catalyzed by cell extract or a partially purified enzyme preparation of E. ramulus. The degradation of lutcolin by resting cells of E. ramulus resulted in the formation of the intermediate eriodictyol, which was identified by high-performance liquid chromatography and mass spectrometry analysis. The observed intermediates o f quercetin and luteolin conversion suggest that the degradation pathways i n E. ramulus start with an analogous reduction step followed by different e nzymatic reactions depending on the additional 3-hydroxyl group present in the flavonol structure.