Kengen S W, Luesink E J, Stams A J, Zehnder A J
Department of Microbiology, Wageningen Agricultural University, The Netherlands.
Eur J Biochem. 1993 Apr 1;213(1):305-12. doi: 10.1111/j.1432-1033.1993.tb17763.x.
Cell-free extracts of cellobiose-grown cells of the hyperthermophile Pyrococcus furiosus contain very high activities (19.8 U/mg) of a beta-glucosidase. The cytoplasmic enzyme was purified 22-fold to apparent homogeneity, indicating that the enzyme comprises nearly 5% of the total cell protein. The native beta-glucosidase has a molecular mass of 230 +/- 20 kDa, composed of 58 +/- 2-kDa subunits. The enzyme has a pI of 4.40. Thiol groups are not essential for activity, nor is the enzyme dependent on divalent cations or a high ionic strength. The enzyme shows optimum activity at pH 5.0 and 102-105 degrees C. From Lineweaver-Burk plots, Vmax values of 470 U/mg and 700 U/mg were found for cellobiose (Km = 20 mM) and p-nitrophenyl-beta-D-glucopyranoside (Km = 0.15 mM), respectively. The purified enzyme also exhibits high beta-galactosidase activity and beta-xylosidase activity, but shows no activity towards alpha-linked disaccharides or beta-linked polymers, like cellulose. The purified beta-glucosidase shows a remarkable thermostability with a half life of 85 h at 100 degrees C and 13 h at 110 degrees C.
嗜热栖热菌（Pyrococcus furiosus）利用纤维二糖生长的细胞的无细胞提取物含有活性非常高（19.8 U/mg）的β-葡萄糖苷酶。这种胞质酶被纯化了22倍，达到了表观均一性，这表明该酶占细胞总蛋白的近5%。天然β-葡萄糖苷酶的分子量为230±20 kDa，由58±2 kDa的亚基组成。该酶的pI为4.40。巯基对活性不是必需的，该酶也不依赖于二价阳离子或高离子强度。该酶在pH 5.0和102 - 105℃时表现出最佳活性。根据Lineweaver - Burk图，纤维二糖（Km = 20 mM）和对硝基苯基 - β - D - 吡喃葡萄糖苷（Km = 0.15 mM）的Vmax值分别为470 U/mg和700 U/mg。纯化后的酶还表现出高β-半乳糖苷酶活性和β-木糖苷酶活性，但对α-连接的二糖或β-连接的聚合物（如纤维素）没有活性。纯化后的β-葡萄糖苷酶具有显著的热稳定性，在100℃下的半衰期为85小时，在110℃下为13小时。
