Purification of cytosolic β-glucosidase from pig liver and its reactivity towards flavonoid glycosides

• Published in: Biochimica et biophysica acta Vol. 1435; no. 1; pp. 110 - 116
• Main Authors: Lambert, Nigel, Kroon, Paul A, Faulds, Craig B, Plumb, Geoff W, McLauchlan, W.Russell, Day, Andrea J, Williamson, Gary
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 16.11.1999
• Subjects: Animals; beta-Glucosidase - antagonists & inhibitors; beta-Glucosidase - chemistry; beta-Glucosidase - isolation & purification; Cytosol - enzymology; Cytosolic; Flavonoid; Flavonoids - chemistry; Glucoside; Glycosides - chemistry; Hydrolysis; Kinetics; Liver - enzymology; Mammalian; Swine; β-Glucosidase; β-Glucosidase; Cytosolic; Flavonoid; Glucoside; Mammalian
• ISSN: 0167-4838; 0006-3002; 1879-2588
• DOI: 10.1016/S0167-4838(99)00213-7

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 β-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 β-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 μM 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 β-glucosidase can deglycosylate some, but not all, common dietary flavonoid glycosides. This enzyme may, therefore, be important in the metabolism of these compounds.