Exo‐glucosidase activity and substrate specificity of the beta‐glycosidase isolated from the extreme thermophile Sulfolobus solfataricus

The enzyme with beta‐galactosidase activity from Sulfolobus solfataricus strain MT‐4, like other enzymes of this type isolated from thermophilic sources, has broad specificity for beta‐D‐gluco‐, fuco‐ and galacto‐sides. The beta‐galactosidase activity was purified by a new procedure that improved yields (44%) and final specific activity (182 units mg‐1 at 75 degrees C using chromogenic beta‐D‐galactoside as substrate). The enzyme hydrolysed a large number of beta‐linked glycoside dimers and oligomers; chromogenic beta‐glucosides and beta‐fucosides are the preferred substrates, and kinetic analysis indicated that they bind to a common catalytic site. The order of catalytic efficiency was beta 1–3 > beta 1–4 > beta 1–6 and cellotetraose > cellotriose > cellobiose for glucose dimers and oliogomers respectively. The cleavage occurred at the non‐reducing end of the oligosaccharide, and the enzyme showed noticeable specificity also for the aglycone part of substrates. From these results the enzyme from S. solfataricus strain MT‐4 is defined as a true glycosyl hydrolase with remarkable exo‐glucosidase activity and it is designated S beta‐gly.