Thermostability and Physicochemical Properties of Endo- and Exoglucanases of Thermophilic Microscopic Fungi

E. G. Kvesitadze,¹ D. N. Nizharadze,¹ T. Sh. Buachidze,¹ and G. I. Kvesitadze^1,2

¹Durmishidze Institute of Plant Biochemistry, Georgian Academy of Sciences, Alleya Davida Agmashenebeli, 10-i km, Tbilisi, 380059 Georgia; fax: (8-832) 98-94-79.

²To whom correspondence should be addressed.

Submitted August 19, 1996; revision submitted October 11, 1996.

The thermostability of endo- and exoglucanases of thermophilic mycelial fungi was studied. Increasing the cultivation temperature of a thermophilic culture of Allesheria terrestris from 40 to 48-49°C results in the formation of a new endoglucanase; it is inactivated only by 20% at 65°C for 6 h in the absence of the substrate. A method for purification of the enzyme was developed and the properties of the enzyme were studied. The molecular weight of the enzyme is 69 kD; the isoelectric point (pI) is 6.4 and the Michaelis constant (K_m) is 6.6 g/liter. The thermostable endoglucanase of A. terrestris reacts with polyclonal antibodies against the unstable endoglucanase of Trichoderma reesei. Screening of the thermophilic fungi exoglucanases indicates the presence of the trace amounts of cellobiohydrolases in the filtrates of some thermophilic fungal cultures. The beta-glucosidases from thermophilic mycelial fungi are homologous, high-molecular-weight proteins (210-230 kD) consisting of 6 subunits; at relatively high temperature (50-55°C) they dissociate to less active trimers and then to monomers.

KEY WORDS: mycelial fungi, endoglucanase, exoglucanase, thermostability, oligomeric protein.

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