Abdel-Naby M A
Department of Chemistry of Natural and Microbial Products, National Research Center, Dokki, Cairo, Egypt.
Appl Biochem Biotechnol. 1993 Jan-Feb;38(1-2):69-81. doi: 10.1007/BF02916413.
Aspergillus niger NRC 107 xylanase and beta-xylosidase were immobilized on various carriers by different methods of immobilization, including physical absorption, covalent binding, ionic binding, and entrapment. The immobilized enzymes were prepared by physical adsorption on tannin-chitosan, ionic binding onto Dowex-50W, covalent binding on chitosan beads through glutaraldehyde, and entrapment in polyacrylamide had the highest activities. In most cases, the optimum pH of the immobilized enzymes were shifted to lower than those of free enzymes. The optimum reaction temperature of immobilized xylanase was shifted from 50C to 52.5-65C, whereas that of immobilized beta-xylosidase was shifted from 45C to 50-60C. The Km values of immobilized enzymes were higher than those of native enzymes. The operational stability of the immobilized enzymes was evaluated in continuous operation in packed-bead column-type reactors. The enzymes covalently bounded to chitosan showed the highest operational stability. However, the enzymes immobilized by physical absorption or by ionic binding showed a low operational stability. The enzymes entrapped in polyacrylamide exhibited lower activity, but better operational stability.
黑曲霉NRC 107木聚糖酶和β-木糖苷酶通过不同的固定化方法固定在各种载体上，包括物理吸附、共价结合、离子结合和包埋。通过单宁-壳聚糖物理吸附、Dowex-50W离子结合、戊二醛共价结合在壳聚糖珠上以及聚丙烯酰胺包埋制备的固定化酶具有最高活性。在大多数情况下，固定化酶的最适pH值向低于游离酶的方向移动。固定化木聚糖酶的最适反应温度从50℃移至52.5 - 65℃，而固定化β-木糖苷酶的最适反应温度从45℃移至50 - 60℃。固定化酶的Km值高于天然酶。在填充珠柱式反应器中连续操作评估固定化酶的操作稳定性。与壳聚糖共价结合的酶表现出最高的操作稳定性。然而，通过物理吸附或离子结合固定的酶表现出较低的操作稳定性。聚丙烯酰胺包埋的酶活性较低，但操作稳定性较好。
