8-Glucosidases thermostability

Table IV. Biochemical Characteristics of Thermostable a-Glucosidase from Clostridium thermohydrosulfuricum 39E...

Another method which may become a useful technique for selective inactivation of cellulases in enzyme mixtures is the use of selective heat inactivation. While establishing the thermostability properties of crude xylanases from a fungal strain Y-94, Mitsuishi et al. (80) observed differential heat labilities of the cellulase and xylanase activities in the culture filtrate. After an incubation period of 20 minutes at 65°C, the xylanase activity was reduced by 5-10% whereas the Avicelase and /3-glucosidase activities were reduced by 100% and 60%, respectively. We have observed a similar temperature dependency of xylanase and cellulase activities in T. auranti-acus. As indicated in Figure 2, treatment of the culture filtrate at 70°C for 20 minutes resulted in less than a 5% loss in xylanase activity whereas cellulase activities were reduced by 40-50%. A similar effect has also been observed for the xylanases and cellulase enzymes produced in culture filtrates from T. harzianum (93). Further work in the area of heat treatments may improve the effectiveness of cellulase inactivation. Since the cellulase activities of some enzyme preparations can be more rapidly inactivated on... 

T. Nagayama, A strong correlation between the increase in number of proline residues and the rise in thermostability of five Bacillus oligo-l,6-glucosidases, Appl. Microbiol. Biotechnd. 1987, 26, 546—551. 

Of potential interest are also the cellulolytic, xylanolytic and pollulan-hydrolyzing activities detected in Thermophilum strains and in AN 1, a member of the Thermococcales [59]. An additional candidate for biotechnical application is also represented by the a-glucosidase from P. furiosus, which exhibits the highest thermostability (to.5(98°C) = 46-48 h) and temperature optimum for activity (105-115 C) compared to all enzymes investigated so far [60] (Table 1). 

Y. Suzuki, Proline residues responsible for thermostability occur with high frequency in the loop regions of an extremely thermostable oligo-l,6-glucosidase from Bacillus thermoglucosidasius KP1006,J. Biol. Chem. 1991, 266(36), 24287-24294. 

Keywords P-glucosidase Immobilization Silica gel Kaolin Thermostability ... 

Another essential factor is the change of thermostability of the enzyme as a consequence of chemical modification and immobilization. We have determined the thermostability of free and immobilized forms of native and acetylated P-glucosidase. The results of these measurements are presented in Figs. 2 and 3. 

As the results presented in Figs. 2 and 3 indicate, thermostability of free, native P-glucosidase is quite high, and after the immobilization on kaolin, it decreases slightly. Acetylation of the enzyme causes substantial decrease of thermostability. Thus, if the native enzyme preserves approximately 45% of its initial activity at 70 °C during 10 min, the acetylated enzyme at the same conditions preserves only 18% of its initial activity. Although acetylation of P-glucosidase decreased the thermostability of the enzyme... 

Fig. 2 Thermostability of P-glucosidase fixtm Novozym 188 preparation in free and immobilized forms. 1 Free enzyme,...

Chemical modification of the enzyme and its immobilization may cause either increase or decrease of thermostability [12-14] depending on the enz)mie, nature of the carrier, and the method of immobilization. As the data Irom Nagamoto et al. [15] indicates, thermostability of 3-glucosidase immobilized on chitosan increases, and the enzyme works successfully at 70 °C during 12 h. Such considerable increase of thermostability that we observed is due to the covalent binding of the enzyme and the carrier. 

K. Goyal, P. Selvakumar, and K. Hayashi. 2001. Molecnlar cloning, purification and characterization of thermostable P-glucosidase from hyperthermophilic strain Thermotoga maritima activity in the presence of alcohols. J. Mol. Catal. B-Enzym. 15 45-53. 

Oswald, P.R. et al., lYoperties of a thermostable beta-glucosidase immobilized using tris(hydroxymethyl) phosphine as a highly effective coupling agent, Enzyme Microb. Technol., 23, 14,1998. 

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