Epidemiological studies indicate that a high intake of flavonoids is associated with an improved health status. Tea is one of the most abundant sources of flavonoids in the human diet. The bioavailability and biotransformation of tea flavonoids are, however, not clearly understood. The aim of the present study was to investigate the metabolism of black tea via a nonspecific screening method. (1)H nuclear magnetic resonance (NMR) spectroscopy was used to obtain nonselective profiles of urine samples collected from three human volunteers before and after a single dose of black tea. The complex spectroscopic profiles were interpreted with the use of pattern recognition techniques. Hippuric acid was confirmed as the major urinary black tea metabolite. One previously unknown metabolite was detected and identified as 1,3-dihydroxyphenyl-2-O-sulfate (sulfate conjugate of pyrogallol) using HPLC directly coupled to mass spectrometry and (1)H NMR spectroscopy. This study shows that NMR-pattern recognition studies can be used for the discovery of unknown flavonoid metabolites in humans.

The backbone dynamics of Fusarium solani pisi cutinase has been studied by a variety of nuclear magnetic resonance experiments to probe internal motions on different time scales. The core of cutinase appears to be highly rigid. The binding site, including the oxyanion hole, is mobile on the microsecond to millisecond time scale, in contrast to the well-defined active site and preformed oxyanion hole elucidated by X-ray crystallography [Martinez, C., de Geus, P., Lauwereys, M., Matthyssens, G., and Cambillau, C. (1992) Nature 356, 615-618]. In this crystal structure, cutinase has a rather open conformation, in which the hydrophobic binding site is exposed. The observed mobility in solution most likely represents the interconversion between open and more closed conformations, like in a true lipase. The opening and closing motions are on a time scale which corresponds with the kinetics of the hydrolysis reaction, i.e., the millisecond range, which suggests that these conformational rearrangements form the rate-limiting step in catalysis. We conclude that the crystal structure probably represents one of the multiple conformations present in solution, which fortuitously is the active conformation. The implications of our findings are discussed with particular reference to the explanation of the lack of interfacial activation as found for cutinase.

No abstract

No abstract