Igarashi Kiyohiko, Tani Tomomi, Rie Kawai, Masahiro Samejima
Department ofBiomaterials Sciences, Graduate School ofAgricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
J Biosci Bioeng. 2003;95(6):572-6. doi: 10.1016/s1389-1723(03)80164-0.
The substrate specificity of an extracellular beta-glucosidase (BGL) from cellulose-degrading culture of the white-rot fungus Phanerochaete chrysosporium was investigated, using a variety of compounds with beta-glucosidic linkages. Amino acid sequencing data for the purified BGL showed that the enzyme is identical to the glycoside hydrolase (GH) family 3 BGL of the same fungus previously reported [Li, B. and Renganathan, V, Appl. Environ. Microbiol., 64, 2748-2754 (1998)]. The BGL can hydrolyze both cellobiose and cellobionolactone, but cellobionolactone was hydrolyzed very much more slowly than cellobiose. Moreover, cellobionolactone inhibited cellobiose hydrolysis by the BGL, suggesting that this enzyme cannot cooperate with cellobiose dehydrogenase (CDH) in cellulose degradation by P. chrysosporium. In addition to cellobiose, BGL utilized various glucosyl-beta-glucosides, such as sophorose, laminaribiose and gentiobiose, as substrates. Among the four substrates, laminaribiose (beta-1,3-glucosidic linkage) was hydrolyzed most effectively. Moreover, the hydrolytic rate of laminarioligosaccharides increased proportionally to the degree of polymerization (DP), and the activity of BGL even towards laminarin with an average DP of 25 was similar to that towards laminaripentaose (DP 5). Therefore, we conclude that the extracellular BGL from P. chrysosporium is primarily a glucan 1,3-beta-glucosidase (EC 3.2.1.58), which might play a role on fungal cell wall metabolism, rather than a beta-glucosidase (EC 3.2.1.21), which might be involved in the hydrolysis of beta-1,4-glucosidic compounds during cellulose degradation.
利用多种具有β-糖苷键的化合物，对来自白腐真菌黄孢原毛平革菌纤维素降解培养物的一种胞外β-葡萄糖苷酶（BGL）的底物特异性进行了研究。纯化的BGL的氨基酸测序数据表明，该酶与先前报道的同一真菌的糖苷水解酶（GH）家族3 BGL相同[Li, B.和Renganathan, V, Appl. Environ. Microbiol., 64, 2748 - 2754 (1998)]。该BGL既能水解纤维二糖，也能水解纤维二糖内酯，但纤维二糖内酯的水解速度比纤维二糖慢得多。此外，纤维二糖内酯抑制BGL对纤维二糖的水解，这表明该酶在黄孢原毛平革菌纤维素降解过程中不能与纤维二糖脱氢酶（CDH）协同作用。除纤维二糖外，BGL还利用多种葡萄糖基-β-葡萄糖苷，如槐糖、昆布二糖和龙胆二糖作为底物。在这四种底物中，昆布二糖（β-1,3-糖苷键）的水解效率最高。此外，昆布寡糖的水解速率与聚合度（DP）成正比，BGL对平均DP为25的海带多糖的活性与对昆布戊糖（DP 5）的活性相似。因此，我们得出结论，黄孢原毛平革菌的胞外BGL主要是一种葡聚糖1,3-β-葡萄糖苷酶（EC 3.2.1.58），可能在真菌细胞壁代谢中发挥作用，而不是一种β-葡萄糖苷酶（EC 3.2.1.21），后者可能参与纤维素降解过程中β-1,4-糖苷化合物的水解。
