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.

Individual molecules of thermostable alkaline phosphatase support different catalytic rates at room temperature.

Thermus thermophilus cells were grown at 70 degrees C, lysed and the lysate subjected to single molecule alkaline phosphatase assays, using a capillary electrophoresis laser-induced fluorescence detection-based method. The enzyme was found to be heterogeneous with respect to catalytic rate when assayed at room temperature. Turnover numbers ranged 12-fold, with an average of 400 +/- 200 reactions/min for the 80 molecules assayed.