Broad substrate specificity glycosidase. Releases glucose from soluble glucooligomers, with a preference for longer oligomers; acts more readily on cellotetraose than on cellobiose. Displays similar activities towards the disaccharides lactose and cellobiose. Is also able to hydrolyze various aryl-beta-glycosides in vitro. Hydrolysis of (1->4)-linkages in (1->4)-beta-D-glucans, to remove successive glucose units. Hydrolysis of terminal, non-reducing beta-D-glucosyl residues with release of beta-D-glucose. Activated by glucose up to 200 mM when p-nitrophenyl-beta-glucoside is used as the substrate. This activation by end product concentrations may be due to a transglycosylation activity of the enzyme. kcat is 285.0, 345.7 and 333.7 sec(-1) for the hydrolysis of cellobiose, cellotriose and cellotetraose, respectively. Optimum pH is 6.5. Optimum temperature is 95 degrees Celsius. Is highly thermostable, retaining 85% activity after incubation for 9 hours at 90 degrees Celsius and 88% activity after 1 hour at 95 degrees Celsius. Glycan metabolism; cellulose degradation. Glycan metabolism; beta-D-glucan degradation. Monomer. Belongs to the glycosyl hydrolase 1 family. Extended N-terminus.