Effect of phosphate anion on the activity and stability of endoxylanase from bacillus sp.

Abstract

Endo-type xylanase which was originated from Bacillus sp. was purified and characterized. The molecular weight and pI value of this endoxylanase were 20.4 kDa and 10.6, respectively. The optimum temperature of enzyme reaction was 60℃ and optimum pH was 7. Because of high pI value, the net charge of this enzyme in pH 7 is positive. Therefore it was suspected that endoxylanase structure can be influenced by ions. Various salts were tested for the activity and stability of xylanase. As a result, not only the stability and but also the activity of endoxylanase (E.C 3.2.1.8) was affected by phosphate anion ($HPO_4^{2-}$). The $T_m$ value of xylanase increased up to 74.5℃ in the presence of 1.2 M $K_2HPO_4$. And the affinity toward substrate, xylan, increases along with $K_2HPO_4$ concentration. Xylanase activity was enhanced up to approximately 600 \% in the presence of 0.6 M $K_2HPO_4$. These seem to be resulted from the change of conformation by the binding of $HPO_4^{2-}$ ions at the surface of folded xylanase.