Orthophosphate anion enhances the stability and activity of endoxylanase from Bacillus sp.

Endoxylanase, for which the optimum temperature is 60 degreesC (optimum pH 7), is labile to heat. Because the isoelectric point (pl) value of this xyl anase is 10.6, the net charge of this enzyme is positive at pH 7. Thus, ion s are likely to influence its enzyme structure and the thermal stability of endoxylanase may improve. Among the various ions tested, orthophosphate an ion (HPO42-) was found to significantly improve not only the stability but the activity of xylanase. When K2HPO4 concentration was increased from 50 m M to 1.2 M, the T-m value of xylanase was increased from 60.0 degreesC to 7 4.5 degreesC. The affinity of xylanase on xylan also increased along with K 2HPO4 concentration. Thus, the xylanase activity at 0.6 M K2HPO4 was 2.3-fo ld higher than that at 50 mM K2HPO4, and 120.2-fold higher than that in 40 mM MOPS buffer. This enhanced activity in the presence of K2HPO4 probably t akes place because the orthophosphate anion affects the binding and catalyt ic residues of endoxylanase. (C) 2001 John Wiley & Sons, Inc.