Purification and characterization of an isoflavones conjugate hydrolyzing β-glucosidase (ICHG) from Cyamopsis tetragonoloba (guar)

Abstract

A β-glucosidase with high specific activity towards isoflavone glycosidic conjugates was purified from seeds of Guar (Cyamopsis tetragonoloba) by ammonium sulphate precipitation followed by size exclusion and ion exchange chromatography. The pH and temperature optima of the purified Isoflavones conjugate hydrolyzing β-glucosidase (ICHG) were found to be pH 4.5 and 37 °C, respectively. The enzyme was relatively stable at higher temperatures. Effect of different divalent metal ions was studied and it was found that Cobalt and Mercury ions completely inhibited the enzyme activity. Km and Vmax of the purified isoflavones conjugates hydrolyzing β-glucosidases (ICHG) was 0.86 mM and 6.6 IU/mg respectively. The enzyme was most likely a trimer (approximate Mr 150 kDa) with potential subunits of 50 kDa. The purified enzyme showed activity against isoflavone conjugate glycosides viz daidzin and genistin but was inactive towards other flavonoid conjugates. The product conversion was confirmed by HPTLC and HRMS analysis. The MALDI-TOF analysis of the ICHG showed a score greater than 78 with 20 matches in MASCOT software. The five resultant peptides obtained had highest similarity in sequence with β-glucosidase from Cicer arietinum. The β-glucosidase from the C. arietinum has also been reported to exhibit the isoflavone conjugate hydrolyzing properties thus confirming the nature of the enzyme purified from the Guar seeds. Keywords: Cyamopsis tetragonoloba, β-glucosidase, Legume, Isoflavonoid Glycosides