THERMOSTABLE BETA-GALACTOSIDASE FROM THE ARCHAEBACTERIUM SULFOLOBUS-SOLFATARICUS - PURIFICATION AND PROPERTIES

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. Copyright © 1990, Wiley Blackwell. All rights reserved