The utility of Hmp for NO• consumption and tolerance decreases with increased NO• delivery rate.

<p><b>(A)</b> Experimentally measured NO• concentration profiles following addition of 0.5 mM PAPA to a culture of wild-type (solid red line) or Δ<i>hmp</i> (solid blue line) <i>E. coli</i> at an OD₆₀₀ of 0.05. Lines depict the mean of three independent experiments, and error bars (light red and light blue for wild-type and Δ<i>hmp</i>, respectively) represent the standard error of the mean. Also shown are the corresponding model-predicted NO• concentration profiles for wild-type (dark red dashed line) or Δ<i>hmp</i> (dark blue dotted line) cultures. <b>(B)</b>. Predicted cumulative concentration (per unit cellular volume) of [2Fe-2S] and [4Fe-4S] clusters damaged following DPTA (purple) or PAPA (teal) treatment of wild-type (solid lines) and Δ<i>hmp</i> cultures (dashed lines) is plotted as a function of the model parameter governing the rate of [Fe-S] nitrosylation by NO• (<i>k</i>_NO•-[Fe-S]). <b>(C)</b> Predicted durations of cytochrome <i>bd</i> (Cyd) inhibition by NO•, defined as the time required for the percentage of NO•-bound Cyd to drop below 50% of the total Cyd concentration. <b>(D)</b> Experimentally measured growth curves (quantified by OD₆₀₀) for wild-type and Δ<i>hmp</i> cultures following treatment with 0.5 mM of DPTA or PAPA demonstrate more comparable duration of bacteriostasis between wild-type and Δ<i>hmp</i> for treatment with PAPA than DPTA. Due to the faster NO• delivery kinetics associated with PAPA, OD₆₀₀ readings were taken more frequently (20 min intervals) than with DPTA (30 min intervals). After addition of DPTA to Δ<i>hmp</i> cells, growth resumption was not observed within the 10 h timeframe of the experiment.