AN EXTREMELY THERMOSTABLE BETA-GLUCOSIDASE FROM THE HYPERTHERMOPHILIC ARCHAEON PYROCOCCUS-FURIOSUS - A COMPARISON WITH OTHER GLYCOSIDASES

Pyrococcus furious harbours several hydrolytic enzyme activities that enable growth on a variety of polymeric substrates like proteins and polysaccharides. Recently, the organism was shown to exhibit an extremely high beta-glucosidase activity, apparently involved in hydrolysis of cellobiose. The cytoplasmic enzyme was purified to homogeneity and its properties were compared with those bf other glycosidases. This comparison can be summarized as follows: i) the beta-glucosidase activity in cell-free extracts is at least 100-fold higher than the P. furiosus alpha-glucosidase activity; ii) the beta-glucosidase comprises 5% of total cell protein as to only 0.3% for the alpha-glucosidase; iii) with respect to substrate specifity, K-m, pI, and pH-optimum the P. furiosus beta-glucosidase resembles other beta-glucosidases from microorganisms from lower temperature ranges; iv) compared to these beta-glucosidases the P. furiosus enzyme exhibits an enhanced general stability; v) a high similarity is observed with a beta-galacto/glucosidase from the hyperthermophile Sulfolobus solfataricus. vi) besides intrinsic features of the enzyme, extrinsic organic compounds appear to determine thermostability of the beta-glucosidase.