A Beta-glucosidase with Beta-xylosidase Activity from the Digestive Juice of the Land Crab Cardisoma armatum

A bifunctional beta-glucosidase/beta-xylosidase enzyme from land crab Cardisoma armatum was purified to homogeneity by anion-exchange, size-exclusion, cation-exchange and hydrophobic interaction chromatographies and characterized to explore his suitability in biotechnology and to elucidate his role in biodegradation of plant material. The enzyme showed a single protein band and its relative molecular weight was estimated to be 69.81 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and 115.24 kDa by gel filtration, indicating that the enzyme should be monomeric or homo-oligomeric enzyme. The specific activities towards para-nitrophenyl-beta-D-glucopyranoside and para-nitrophenyl-beta-D-xylopyranoside were 74.16 ± 2.10 -4 and 88.60 ± 2.10 -3 U/mg of protein, respectively. This enzyme was optimally active at pH 5.6 and at 60 °C, and was stable at pH range 4.6 to 6.6. The only substrates that were hydrolyzed by the purified enzyme were para-nitrophenyl-beta-D-glucopyranoside, para-nitrophenyl-beta-D-xylopyranoside, xylobiose, cellobiose and cellodextrins. The enzyme was specific for substrates with a beta-(1,4)-glucosidic linkages and was an exo-glycosidase. The catalytic efficiencies values for beta-D-1,4-glucoside and beta-D-1,4-xyloside were respectively 1666.67 and 132.89 mM -1 s -1 . The purified enzyme is a beta-glucosidase with beta-xylosidase activity, which takes effect after actions of endo-enzymes and exo-enzymes and it hydrolyzes cellobiose and xylobiose in glucose and xylose, respectively. However, the beta-glucosidase/beta-xylosidase catalyzed both hydrolysis and transglycosylation.