利用重叠延伸PCR技术对嗜热脂肪芽孢杆菌木聚糖酶XynA活性中心附近的H297位点突变为F。将XynA及XynA_H297F在大肠杆菌BL21（DE3）中实施了表达、纯化以及酶学性质研究。比较研究野生型木聚糖酶XynA和突变体XynA_H297P的酶学性质发现，突变前后木聚糖酶的最适反应pH均为5.5，在pH 4-10的缓冲液中处理20 h后残余酶活均在90%以上，均具有较好的pH稳定性。XynA最适反应温度为70 ℃，80 ℃处理20min后只有10%的残余酶活；XynA_H297最适反应温度为75 ℃，且相同处理条件下XynA_H297仍具有30%左右的残余活性，说明突变体的热稳定性有一定程度提高。与XynA相比，XynA_H297F的动力学参数Km、Vmax和Kcat均增大，说明突变后酶对底物的亲和力降低，但催化速率有所提高。

Overlapping extension PCR was used to replace the amino acid residue His 297 (H) by Phe (F), near the activity center of XynA from Geobacillus stearothermophilus. XynA and XynA_H297F were separately expressed in Escherichia coli BL21(DE3). Both xylanases were purified and characterized. The optimum pH of XynA_H297F was 5.5, similar to XynA. After treated in pH4-10 buffers over 20hs, the residual activities of XynA and XynA_H297F were above 90%, which indicated both of them had good pH stability.The optimum temperature of XynA_H297F was increased from 70 °C to 75 °C, relative to XynA. In addition, the XynA and XynA_H297F remained about 10% and 30% residual activities after incubated at 80 °C for 20 min, respectively. It proved that the thermal stability of XynA_H297F was improved at certain degree. Compared with XynA, XynA_H297F displayed increases in Km, Vmax and Kcat. The results showed that the affinity of enzyme to substrate was decreased, but the catalytic rate was increased.