Newly Induced β-Galactosidase Molecules Have a Higher Activity Than the Basally Expressed Enzyme

Abstract

Objective: The objective of this study was to compare the activities of individual molecules of induced and basally expressed Escherichia coli β-galactosidase. Background Data: Single-molecule assays of enzymes have determined that individual molecules are not identical. They differ with respect to catalytic rate. The structural cause and cellular role of this microheterogeneity is as yet unknown. Methods: E. coli were grown and induced to produce β-galactosidase by treatment with isopropyl-β-D-thiogalactopyranoside. Cells were lysed and the β-galactosidase assayed with capillary electrophoresis instrumentation utilizing post-column, laser-induced fluorescence detection. The enzyme obtained from treated cells were compared to that from untreated cells. Results: The activity of newly induced β-galactosidase was found to be approximately 20% greater than that of the basally expressed enzyme. This measured difference is statistically significant. Conclusions: Production of β-galactosidase in E. coli under differing conditions results in differences in the activities of the individual enzyme molecules.