嗜热拟青霉木糖苷酶的性质及其与木聚糖酶的协同作用

Characterization of a β-Xylosidase from Paecilomyces thermophila and Its Synergistic Action with the Endogenous Xylanase

嗜热拟青霉(Paecilomyces thermophila)J18利用玉米芯能产胞外木糖苷酶,通过(NH_4)_2SO_4沉淀、DEAE-52离子交换层析及Q-琼脂糖凝肢-FF(QSFF)离子交换层析从上清液纯化得到了电泳纯的木糖苷酶,纯化倍数为31.9倍,回收率为2.27%。SDS-PAG E及Superdex-75凝胶过滤层析测定木糖苷酶的分子量分别为53.5 ku和51.8 ku。该酶最适温度及pH分别为55℃和pH 6.5。木糖苷酶能够水解木二糖和低聚木糖但不能水解木聚糖,水解低聚木糖的相对速率随聚合度增加而增加。该酶对木糖的抑制常数Ki值为139 mmol/L,具有很高的木糖耐受性。木糖苷酶与内源木聚糖酶一起水解木聚糖产生更多的还原糖,表现出协同作用。

An extracellular β-xylosidase from the thermophilic fungus Paecilomyces thermophila J18 was purified 31.9-fold to homogeneity with a recovery yield of 2.27% from the cell-free culture supernatant by ammonium sulfate precipitation, DEAE-52 and Q-Sepharose Fast Flow chromatography. It appeared as a single protein band on SDS-PAGE with a molecular mass of approx 53.5 ku. The molecular mass of β-xylosidase was 51.8 ku determined by Superdex 75 gel filtration. The enzyme exhibited an optimal activity at 55℃ and pH 6.5, respectively. The purified enzyme hydrolyzed xylobiose and higher xylooligosaccharides but was inactive against xylan substrates. The rate of xylose released from xylooligosaccharides by the purified enzyme increased with increasing chain length. The enzyme was competitively inhibited by xylose with a Ki value of 139 mmol/L and exhibited a high xylose tolerance. Release of reducing sugars from xylans by a purified xylanase produced by the same strain increased remarkably in the presence of β-xylosidase. These properties are attractive features for potential applications in bioconversion.