Characterization of β-Xylosidase and α-L-Arabinofuranosidase Activities From Thermomonospora Fusca BD25

Thermomonospora fusca BD25 produces relatively high levels of activity of β-xylosidase and α-L-arabinofuranosidase. The aim of the work described in this study was to characterize some properties of β-xylosidase and α-L-arabinofuranosidase produced by T. fusca BD25 when growing on oat spelt xylan as the main carbon and energy sources. The substrates p-NPX and p-NPA reacted with β-xylosidase and α-L-arabinofuranosidase with specific activities of 4.01 U mg-1 protein and 0.35 U mg-1 protein, respectively. The β-xylosidase remained stable at up to 65 °C, but α-Larabinofuranosidase lost 10 % of its maximum activity at 55 °C. β-xylosidase and α-Larabinofuranosidase activities remained at 86 % and 83 % of their maximum activities after 9 h of incubation at 50 °C. The maximum relative β-xylosidase activity occurred (0.82 U mg-1 protein) at pH 8.0 with a 50 % decrease of maximum relative activity occurring at pH 4.5 and 10. α-Larabinofuranosidase exhibited maximum relative activity (0.136 U mg-1 protein) at pH 9.0 with 54 % and 55 % activities remaining at pH of 4.5 and 11, respectively. The apparent Km values for the crude β-xylosidase and α-L-arabinofuranosidase preparations were 0.5 mM of p-NPX and 0.18 mM of pNPA, while the Vmax values were 0.83 μmol p-nitrophenol ml-1 min-1 and 0.04 μmol p-nitrophenol ml1 min-1, respectively. The addition of D-xylose (10 mM) to the reaction mixture caused a 10 % reduction in β-xylosidase activity as the end-product inhibitor. However, a 15 % reduction in α-Larabinofuranosidase activity was detected when L-arabinose (10 mM) was added to the reaction mixture.