Fungal beta-glucosidases (BGs) from glucoside hydrolase family 3 (GH3) are industrially important enzymes, which convert cellooligosaccharides into glucose; the end product of the cellulolytic process. They are highly active against the β-1,4 glycosidic bond in soluble substrates but typically reported to be inactive against insoluble cellulose. We studied the activity of four fungal GH3 BGs on cellulose and found significant activity. At low temperatures (10 ℃), we derived the approximate kinetic parameters kcat = 0.3 ± 0.1 s−1 and KM = 80 ± 30 g/l for a BG from Aspergillus fumigatus (AfBG) acting on Avicel. Interestingly, this maximal turnover is higher than reported values for typical cellobiohydrolases (CBH) at this temperature and comparable to those of endoglucanases (EG). The specificity constant of AfGB on Avicel was only moderately lowered compared to values for EGs and CBHs. Overall these observations suggest a significant promiscuous side activity of the investigated GH3 BGs on insoluble cellulose. This challenges the traditional definition of a BG and supports suggestions that functional classes of cellulolytic enzymes may represent a continuum of overlapping modes of action.

中文翻译：

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真菌β-葡萄糖苷酶对纤维素的活性。

来自葡糖苷水解酶家族 3 (GH3) 的真菌 β-葡糖苷酶 (BG) 是工业上重要的酶，可将纤维寡糖转化为葡萄糖；纤维素分解过程的最终产物。它们对可溶性底物中的 β-1,4 糖苷键具有高度活性，但通常据报道对不溶性纤维素无活性。我们研究了四种真菌 GH3 BG 对纤维素的活性，并发现了显着的活性。在低温 (10 ℃) 下，我们推导出烟曲霉 (AfBG) 作用于 Avicel 的 BG 的近似动力学参数 kcat = 0.3 ± 0.1 s-1 和 KM = 80 ± 30 g/l。有趣的是，该最大周转率高于该温度下典型纤维二糖水解酶 (CBH) 的报告值，并且与内切葡聚糖酶 (EG) 的值相当。与 EGs 和 CBHs 的值相比，AfGB 在 Avicel 上的特异性常数仅适度降低。总体而言，这些观察结果表明所研究的 GH3 BG 对不溶性纤维素具有显着的混杂副活性。这挑战了 BG 的传统定义，并支持纤维素分解酶的功能类别可能代表重叠作用模式的连续体的建议。