Synthesis and characterization of novel astragalin galactosides using β-galactosidase from Bacillus circulans

• Published in: Enzyme and microbial technology 2017-08, Vol.103, p.59-67
• Main Authors: Han, Songhee, Hanh Nguyen, Thi Thanh, Hur, Jaewon, Kim, Nahyun M., Kim, Seong-Bo, Hwang, Kyeong-Hwan, Moon, Young-Hwan, Kang, Choongil, Chung, Byoungsang, Kim, Young-Min, Kim, Tae Sung, Park, Jun-Seong, Kim, Doman
• Format: Article
• Language: English
• Subjects: ACE inhibition; Angiotensin-Converting Enzyme Inhibitors - chemistry; Angiotensin-Converting Enzyme Inhibitors - pharmacology; Antioxidant activity; Astragalin; Astragalin galactoside; Bacillus - enzymology; Bacterial Proteins - metabolism; beta-Galactosidase - metabolism; Cell Survival - drug effects; Free Radical Scavengers - chemistry; Free Radical Scavengers - pharmacology; Galactosides - biosynthesis; Galactosides - chemistry; Galactosides - pharmacology; HEK293 Cells; Humans; Industrial Microbiology; Kaempferols - biosynthesis; Kaempferols - chemistry; Kaempferols - pharmacology; Magnetic Resonance Spectroscopy; Molecular Structure; Solubility; β-Galactosidase
• ISSN: 0141-0229; 1879-0909
• DOI: 10.1016/j.enzmictec.2017.05.003

[Display omitted] •Novel astragalin-galactosides were synthesized using β-galactosidase and lactose.•Response surface method was used to optimize astragalin conversion yields.•Chemical structures of novel Ast-Gals were determined by NMR.•Water solubility of Ast-Gal2 was 1500 fold higher compared to astragalin.•Ast-Gals retained the antioxidant and ACE inhibitory activities of Ast. Astragalin (kaempferol-3-O-β-d-glucopyranoside, Ast) is a kind of flavonoid known to have anti-oxidant, anti-HIV, anti-allergic, and anti-inflammatory effects. It has low solubility in water. In this study, novel astragalin galactosides (Ast-Gals) were synthesized using β-galactosidase from Bacillus circulans and reaction conditions were optimized to increase the conversion yield of astragallin. Purified Ast-Gal1 (11.6% of Ast used, w/w) and Ast-Gal2 (6.7% of Ast used, w/w) were obtained by medium pressure chromatography (MPLC) with silica C18 column and open column packed with Sephadex LH-20. The structures of Ast-Gal1 and Ast-Gal2 were identified by nuclear magnetic resonance (NMR) to be kaempferol-3-O-β-d-glucopyranosyl-(1→6)-β-d-galactopyranoside and kaempferol-3-O-β-d-glucopyranosyl-(1→6)-β-d-galactopyranosyl-(1→4)-β-d-galactopyranoside, respectively. The water solubility of Ast, Ast-Gal1, and Ast-Gal2 were 28.2±1.2mg/L, 38,300±3.5mg/L, and 38,800±2.8mg/L, respectively. The SC50 value (the concentration required to scavenge 50% of the ABTS+) of Ast, Ast-Gal1, and Ast-Gal2 were 5.1±1.6μM, 6.5±0.4μM, and 4.9±1.1μM, respectively. The IC50 values (the half maximal inhibitory concentration) of Ast, Ast-Gal1, and Ast-Gal2 against angiotensin converting enzyme (ACE) were 171.0±1.2μM, 186.0μM, and 139.0±0.2μM, respectively.