Studies of alkyl side chains on PQS. Fe reverses inhibition by side chain congeners, but combination of congeners with Fe does not boost metabolism above Fe alone. Target 10AF, all congeners studied at 12.5 μg/mL, DMSO controls are shown. Dilutions of Fe were made from 0.01 to 1000 μM final concentrations (these are the numbers on the x axis). In some experiments there were visible solubility problems with Fe 100–1000 μM, and the study values were the same as the next lower concentration; those bars are omitted. (A) C3-PQS (left bar) inhibits 10AF (p < 0.01) compared to control (right bar). Fe begins to reverse C3-PQS effect at 0.01 μM Fe, and with concentrations of Fe 100 μM with C3-PQS, are all at p < 0.001 compared to C3-PQS alone. No significant boosting across these concentrations above Fe alone, for C3-PQS + Fe. (B) C5-PQS (left bar) inhibits 10AF (p < 0.001) compared to controls (right bar). Fe evidently begins to reverse C5-PQS effect at 0.1 μM Fe, and at concentrations of Fe 1 to 1000 μM with C5-PQS, loss of inhibition is significant (p < 0.001) compared to C5-PQS alone. No significant boosting across these concentrations above Fe alone, for C5-PQS + Fe. (C) C9-PQS (left bar) inhibits 10AF (p < 0.01) compared to controls (right bar). Fe reverses C9-PQS effect at 0.1 to 10 μM Fe, loss of inhibition is significant (p < 0.001) compared to C9-PQS alone. No significant boosting across these concentrations above Fe alone, for C9-PQS + Fe.