An Extremely Thermostable β-Glucosidase from the Hyperthermophilic ArchaeonPyrococcus Furiosus; A Comparison with Other Glycosidases

Pyrococcus furiosus 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 β-glucosidase activity, apparently involved in hydrolysis of cellobiose. The cytoplasmic enzyme was purified to homogeneity and its properties were compared with those of other glycosidases. This comparison can be summarized as follows: i) the β-glucosidase activity in cell-free extracts is at least 100-fold higher than the P. furiosus α-glucosidase activity; ii) the β-glucosidase comprises 5% of total cell protein as to only 0.3% for the α-glucosidase; iii) with respect to substrate specifity, Km, pI, and pH-optimum the P. furiosus β-glucosidase resembles other β-glucosidases from microorganisms from lower temperature ranges; iv) compared to these β-glucosidases the P. furiosus enzyme exhibits an enhanced general stability; v) a high similarity is observed with a β-galacto/glucosidase from the hyperthermophile Sulfolobus solfataricus. vi) besides intrinsic features of the enzyme, extrinsic organic compounds appear to determine thermostability of the β-glucosidase.