Fig. 2. Development of the PqsH biochemical assay.

A. Fluorescence emission spectra of PQS and HHQ after excitation at 340 nm. Emission at 450 nm was used to quantify PQS after ethyl acetate extraction of enzyme reactions. B. PQS production is linearly dependent to both time and enzyme concentration. MBP-PqsH (● 12.5 nM, ○ 25 nM, ▼ 37.5 nM, △ 50 nM) was mixed with all substrates and production of PQS was monitored over time. The inset shows reaction velocity vs. enzyme concentration, and the slope of this line reveals an enzyme turnover of 2.5 min⁻¹.