黑胸散白蚁纤维素酶的体外酶学特性

采用DNS法研究了我国广泛分布的一种低等木食性白蚁——黑胸散白蚁纤维素酶的体外酶活特性以了解其纤维素降解机制.结果表明,内切β-1,4-葡聚糖酶(EG)、纤维二糖水解酶(CBH)和β-葡萄糖苷酶(BG)这3种酶的最佳反应时间均为15 min,最佳底物浓度为1%,最适反应pH为5.6,最适反应温度为35℃.在最适反应条件下,EG、CBH和BG的活性分别达到71.3(±13.9)U/mg、5.8(±0.8)U/mg和4.1(±0.7)U/mg.EG在体外的热稳定性较差,在50℃及更高温度酶活很低或完全失活,但该酶对pH稳定性较好,在pH 3.2～8.0范围内酶活力变化不大.Native-PAGE电泳检测到该白蚁体内至少有8种不同的EG活性条带,肠道不同部位纤维素酶活性条带种类不同.这些研究表明,木食性白蚁降解纤维素是一个复杂的过程,需要多种纤维素酶的共同作用.

In vitro Characteristics of the Cellulases from Reticulitermes chinensis Snyder

Reticulitermes chinensis Snyder(Isoptera: Rhinotermitidae) is a wood-feeding lower termite widely distributed in China.For understanding the mechanisms of cellulose degradation in this termite,the in vitro enzyme activities of endo-β-1,4-glucanase(EG),exo-β-1,4-glucanase(namely cellobiohydrolase,CBH),and β-1,4-glucosidase(BG) from the worker termites of R.chinensis were studied with DNS method.The results showed that for the three enzymes,the optimum reaction time,substrate concentration,pH and temperature were 15 min,1%,5.6 and 35 ℃,respectively.Under the above conditions,the activities of EG,CBH,and BG was 71.3(±13.9) U/mg,5.8(±0.8) U/mg and 4.1(±0.7) U/mg,respectively.Endo-β-1,4-glucanase was not stable under high temperature in vitro.The incubation of crude enzyme at above 50 ℃ would result in low activity or inactivation of the enzyme.However,this enzyme was relatively stable in the pH range from 3.2 to 8.0.Native-PAGE electrophoreses showed that there were at least eight different enzyme activity bands corresponding to endo-β-1,4-glucanase distributing in different gut segments in R.chinensis,which indicated the complexity of cellulose degradation process in wood-feeding lower termites.