Effect of a Nonionic Surfactant on the Adsorption and Kinetic Mechanism for the Hydrolysis of Microcrystalline Cellulose by Endoglucanase ￥° and Exoglucanase ￥±

摘要

Effect of a nonionic surfactant, Tween 20 on the adsorption and kinetic mechanism for the hydrolysis of a microcrystalline cellulose, Avicel PH 101, by endoglucanase グ (Endo グ) and exoglucanase ケ (Exo ケ) isolated from Trichoderma viride were studied. The Langmuir isotherm parameters, amount of maximum adsorption (Amax) and adsorption equilibrium constant (Kad) for the adsorption, were obtained in the presence and the absence of nonionic surfactant. On the addition of Tween 20, the Kad and Amax values of Exo ケ were decreased, while those of Endo グ were not affected. These indicate that the adsorption affinity of Exo ケ on the cellulose is weakened by nonionic surfactant, and the surfactant enhanced desorption of Exo ケ from insoluble substrate. The enzymatic hydrolysis of the cellulose can be described by two parallel pseudo-first order reactions using the percentages of easily (Ca) and hardly (Cb) hydrolyzable cellulose in Avicel PH 101 and associated rate constants (ka and kb). The Ca value was increased by adding Tween 20 for all enzyme samples (Exo ケ , Endo グ and their 1:1 mixture) implying that the low-ordered crystalline fraction in the cellulose may be partly dispersed by surfactant. The ka value was not affect by adding Tween 20 for all enzyme samples (Exo ケ, Endo グ and their 1:1 mixture). The kb value of Exo ケ was increased by adding Tween 20, while that of Endo グ was not affected. This suggests that the surfactant helps the Exo ケ desorb from microcrystalline cellulose, and increase the hydrolysis rate. These results were show that the increase of hydrolysis of cellulose by the nonionic surfactant is due to both the activation of Exo ケ and partial defibrillation of the cellulose.