Mechanisms of Protein Sequence Divergence and Incompatibility
Figure 2
Growth rates and PGK cell lysate activities.
Plotted are growth rates (open symbols, right Y axis) and levels of PGK enzymatic activity in crude cell lysates (closed symbols, left Y axis) as a function of the expression inducer (AHT) concentration. Shown are the parental E. coli strain (squares) and its pgk knockout (Δpgk). The latter was supplemented with the pZA plasmid encoding wild-type hPGK (lysine 219; triangles), or its K219S mutant (diamonds). Cells were grown in glycerol-succinate media supplemented with 5 mM glucose and increasing AHT concentrations. Cell suspensions were normalized to the same cell density, lysed, and PGK activity levels in the lysates were determined. The lysate activities were normalized to the activity of the parental E. coli strain MG1655 (3±0.34×105 µmole product/min/mg dry cells). Growth rates are presented as the inverse of the shortest doubling time among time intervals [46] (the shortest doubling time was observed with E. coli MG1655, and was 63±2.8 mins). Error bars represent the standard deviation of ≥3 independent measurements (growth, lysis, and assays).