Thermostable β‐galactosidase from the archaebacteriumSulfolobus solfataricusPurification and properties

Abstract

A thermophilic and thermostable β-galactosidase activity was purified to homogeneity from crude extracts of the archaebacterium Sulfolobus solfataricus, by a procedure including ion-exchange and affinity chromatography. The homogeneous enzyme had a specific activity of 116.4 units/mg at 75°C with o-nitrophenyl β-galactopyranoside as substrate. Molecular mass studies demonstrated that the S. solfataricusβ-galactosidase was a tetramer of 240 ± 8 kDa composed of similar or identical subunits. Comparison of the amino acid composition of β-galactosidase from S. solfataricus with that from Escherichia coli revealed a lower cysteine content and a lower Arg/Lys ratio in the thermophilic enzyme. A rabbit serum, raised against the homogeneous enzyme did not crossreact with β-galactosidase from E. coli. The enzyme, characterized for its reaction requirements and kinetic properties, showed a thermostability and thermophilicity notably greater than those reported for β-galactosidases from other mesophilic and thermophilic sources.