AN EXTREMELY THERMOSTABLE BETA-GLUCOSIDASE FROM THE HYPERTHERMOPHILICARCHAEON 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 p olysaccharides. Recently, the organism was shown to exhibit an extreme ly high beta-glucosidase activity, apparently involved in hydrolysis o f cellobiose. The cytoplasmic enzyme was purified to homogeneity and i ts properties were compared with those bf other glycosidases. This com parison can be summarized as follows: i) the beta-glucosidase activity in cell-free extracts is at least 100-fold higher than the P. furiosu s alpha-glucosidase activity; ii) the beta-glucosidase comprises 5% of total cell protein as to only 0.3% for the alpha-glucosidase; iii) wi th respect to substrate specifity, K-m, pI, and pH-optimum the P. furi osus beta-glucosidase resembles other beta-glucosidases from microorga nisms from lower temperature ranges; iv) compared to these beta-glucos idases 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 fe atures of the enzyme, extrinsic organic compounds appear to determine thermostability of the beta-glucosidase.