| Abstract |
Mutational experiments were performed to improve the cellulase productivity of Aspergillus phoenicis KU175, isolated from the southern part of Korea, as a high cellulase producer. By treatment ultra-violet light and 4-NQO(4-Nitroquinoline-N-Oxide), mutation was induced, and treatment ultra-violet light and 4-NQO (4-Nitroquinoline-N-Oxide), mutation was induced, and A.phoenicis KU175-115 was finally selected for its highest avicelase production. Avicelase production of the mutant was increased about 2 times compared with those of the wild strain. However, activities of other hydrolytic enzymes, such as amylase, protease and nuclease, of the mutant strain didn't show a marked difference compared with those of the nuclease, of the mutant strain didn't show a marked difference compared with the wild strain, except slight increase in ribonuclease activity and slight decrease in glucoamylase activity. Avicelases from the mutant strain selected were purified from wheat bran culture by successive salting out, followed by dialysis and column chromatography, and their charcteristics were compared with those of the wild strain. Avicelase was separated into three peaks in the mutant strain as well as in the case of wild strain. Avicelase II activity of the mutant strain was prominently higher than that of the wild strain, while avicelase I and III activities of those were equivalent. The optimal pH ranges and stability of avicelase II from the mutant strain were pH4-5 and pH3.5-6.0, respectively, as well as in the case of the wild strain. The optimal temperature and thermal stability of avicelase II from the mutant strain were 40-50℃ and 20-55℃, respectively. These results were same as those of the wild strain. By the using of Eadie-Hofastee plot, K_m and V_max of avicelase II from the mutant and the wild strain were calculated to be 2.29mg/ml and 4.84㎍ reducing sugar as glucose per min equally, from the line fitted to the data by the least square method. Activity of avicelase II from the mutant strain was slightly activated by Mg^++ but inhibited by Cu^++, Mn^++ and Zn^++, as well as in the case of the wild strain. Therefore, it was concluded that the mutant didn't induce the formation of another avicelase isozyme, or the changes in the properties of avicelase, but induce the changes in the productively of the same avicelase II by the action of regulatory gene. |
