Purification of cytosolic beta-glucosidase from pig liver and its reactivity towards flavonoid glycosides.
Flavonoid glycosides are common dietary components which may have health-promoting activities. The metabolism of these compounds is thought to influence their bioactivity and uptake from the small intestine. It has been suggested that the enzyme cytosolic beta-glucosidase could deglycosylate certain flavonoid glycosides. To test this hypothesis, the enzyme was purified to homogeneity from pig liver for the first time. It was found to have a molecular weight (55 kDa) and specific activity (with p-nitrophenol glucoside) consistent with other mammalian cytosolic beta-glucosidases. The pure enzyme was indeed found to deglycosylate various flavonoid glycosides. Genistein 7-glucoside, daidzein 7-glucoside, apigenin 7-glucoside and naringenin 7-glucoside all acted as substrates, but we were unable to detect activity with naringenin 7-rhamnoglucoside. Quercetin 4'-glucoside was a substrate, but neither quercetin 3, 4'-diglucoside, quercetin 3-glucoside nor quercetin 3-rhamnoglucoside were deglycosylated. Estimates of K(m) ranged from 25 to 90 microM while those for V(max) were about 10% of that found with the standard artificial substrate p-nitrophenol glucoside. The non-substrate quercetin 3-glucoside was found to partially inhibit deglycosylation of quercetin 4'-glucoside, but it had no effect upon activity with p-nitrophenol glucoside. This study confirms that mammalian cytosolic beta-glucosidase can deglycosylate some, but not all, common dietary flavonoid glycosides. This enzyme may, therefore, be important in the metabolism of these compounds.
Lambert
N
N
Cellular Metabolism Section, Diet, Health and Consumer Sciences Division, Institute of Food Research, Norwich Research Park, Colney, Norwich, UK.
Kroon
P A
PA
Faulds
C B
CB
Plumb
G W
GW
McLauchlan
W R
WR
Day
A J
AJ
Williamson
G
G
D000818:Animals; D003600:Cytosol / Q000201:enzymology; D005419:Flavonoids / Q000737:chemistry; D006027:Glycosides / Q000737:chemistry; D006868:Hydrolysis; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D013552:Swine; D001617:beta-Glucosidase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000302:isolation & purification*
D005419:Flavonoids; D006027:Glycosides; D001617:beta-Glucosidase