Fig. 4
Effect of light exposure and assay reaction time on MP Biomedicals and RR535 IC50 values for DUSP5. DUSP5 PD(WT) initial velocity, monitored utilizing pNPP as the substrate, versus increasing concentrations of (a) MP Biomedicals and B) RR535 (1 to 300 μM) prepared from stock solutions that were either stored in the dark or exposed to room light for 17 days. IC50 values were determined from rate data collected during the first ten minutes of the reaction period. The calculated IC50 ± SE for MP Biomedicals that was stored in the dark was 588 ± 351 μM, compared to 221 ± 11 μM for the same compound when stored exposed to room light (a). RR535 that was stored in the dark did not inhibit DUSP5 PD(WT) activity over the concentration range tested, while the IC50 for light-exposed RR535 was 725 ± 206 μM (b). c MP Biomedicals IC50 values determined as in (a) from rate data collected between 15 and 25 min during the reaction period for compound stored in the dark or exposed to room light were 360 ± 36 μM and 31 ± 1 μM, respectively. d RR535 IC50 values determined as in (b) from rate data collected between 15 and 25 min. Compound stored in the dark did not inhibit DUSP5 PD(WT) activity while light exposed RR535 had an IC50 of 78.8 ± 4.9 μM. Data points represent the mean ± SD of four trials with four wells at each MP Biomedicals and RR535 concentration