Differences in the average single molecule activities of E. coli beta-galactosidase: effect of source, enzyme molecule age and temperature of induction.

Using a capillary electrophoresis-based method, single enzyme molecule assays were performed on E. coli beta-galactosidase from three different sets of samples. The first set consisted of lysates of induced cells from five different strains of the bacteria, as well as two different commercial preparations of the enzyme.