Authors: MÜNİR TUNCER
Abstract: Thermomonospora fuscaBD25 produces relatively high levels of activity of \beta-xylosidase and \alpha-L-arabinofuranosidase. The aim of the work described in this study was to characterize some properties of \beta-xylosidase and \alpha-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 \beta-xylosidase and \alpha-L-arabinofuranosidase with specific activities of 4.01 U mg -1 protein and 0.35 U mg -1 protein, respectively. The \beta-xylosidase remained stable at up to 65 °C, but \alpha-L-arabinofuranosidase lost 10 % of its maximum activity at 55 °C. \beta-xylosidase and \alpha-L-arabinofuranosidase activities remained at 86 % and 83 % of their maximum activities after 9 h of incubation at 50 °C. The maximum relative \beta-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. \alpha-L-arabinofuranosidase 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 K m values for the crude \beta-xylosidase and \alpha-L-arabinofuranosidase preparations were 0.5 mM of p-NPX and 0.18 mM of p-NPA, while the V max values were 0.83 mmol p-nitrophenol ml -1 min -1 and 0.04 mmol p-nitrophenol ml -1 min -1 , respectively. The addition of D-xylose (10 mM) to the reaction mixture caused a 10 % reduction in \beta-xylosidase activity as the end-product inhibitor. However, a 15 % reduction in \alpha-L-arabinofuranosidase activity was detected when L-arabinose (10 mM) was added to the reaction mixture.
Keywords: \beta-xylosidase, \alpha-L-arabinofuranosidase, lignocellulose degradation, Thermomonospora fusca, actinomycete.
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