Characterization of the thermostability of xylanase produced by new isolates of Thermomyces lanuginosus

Characterization of the thermostability of purified enzymes of low and high thermostable xylanase produced by new isolates of T. lanuginosus THKU-9 and THKU-49 were performed. Half-life at 70 degrees C of the purified xylanases from T. lanuginosus THKU-9 and THKU-49, in 50 mM phosphate buffer (pH 6.0) was 178 and 336 min, respectively. These enzymes were unstable at pH 5.0 and completely lost their activity after incubation at 70 degrees C for 30 min. The xylanase produced by THKU-9 retained 87% and 30% activity in 50 mM sodium phosphate buffer (pH 7.0) after 1080 min incubation at 60 degrees C and 70 degrees C, respectively, whereas xylanase produced by THKU-49 retained full activity and 41% activity, respectively. The enzymes were more stable in phosphate buffer than in citrate buffer. When the buffer concentration increased, the half-life of the enzymes decreased significantly. Amino acid sequence analysis of low thermostable T. lanuginosus THKU-9 xylanase and high thermostable T. lanuginosus THKU-49 xylanase showed that high thermostable xylanase had a single substitution (V96G), which is a small hydrophobic amino acid of beta sheet (B5) of the protein located on the outer surface of the enzyme structure.