Heterogeneous properties of individual molecules of beta-galactosidase from the thermophilic bacteria Geobacillus stearothermophilus.

Single enzyme molecule assays were performed on beta-galactosidase from the thermophilic bacteria Geobacillus stearothermophilus using a capillary electrophoresis-based continuous flow assay and the substrate DDAO-beta-D: -galactoside. The enzyme was found to be heterogeneous with respect to catalytic rate, electrophoretic mobility and activation energy of catalysis. Catalytic rate was also found to vary over time for individual molecules at elevated temperature. Comparison with beta-galactosidase from the mesophilic bacteria Escherichia coli showed that the variation in activity over time was less pronounced and the average activation energy of catalysis was lower for the Geobacillus stearothermophilus enzyme. Attempts to measure the properties of individual beta-galactosidase molecules from the thermophilic bacteria Thermus thermophilus and the cold-adapted bacteria Pseudoalteromas haloplanktis using this assay were unsuccessful.