Evidence that β-Galactosidase of Sulfolobus solfataricus Is Only One of Several Activities of a Thermostable β- d -Glycosidase

Abstract

A survey of Sulfolobus isolates showed all to contain thermostable enzyme activities hydrolyzing various glycosidic compounds. Of those not previously reported, the β-glucosidase activity of Sulfolobus solfataricus isolate P2 was chosen for further study and found to have the same kinetics of inactivation, apparent molecular weight, and many (though not all) other biochemical properties of the β-galactosidase also present in this strain. The two activities copurified approximately 850-fold to apparent homogeneity. The enzyme, whose subunit M r was estimated to be 60,000 to 65,000 by gel permeation chromatography of the active enzyme and 70,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the denatured form, hydrolyzed a variety of low-molecular-weight, β-linked glycosides and could account for most of the corresponding activities found in crude extract. Kinetic analyses indicated that chromogenic β- d -galactosides and β- d -glucosides are hydrolyzed at a common active site and that β-glucosides and β-fucosides represent the preferred substrates. The liberation of aglycone from aryl β- d -glucosides was stimulated by alcohols in a manner suggesting specific interaction between alcohol and enzyme.