The concentration ranges are: [HRP] ~nM, [ABTS] = 1 mM, [H2O2] = 4 mM, Azide varying, from 50 mM to 0.0005 mM to 0 mM (control = 100% activity). It can be seen that at dilute concentrations of azide, even with latency of addition of enzyme, the color formation (ABTS radical cation product) is relatively higher with respect to control, whereas at higher azide concentration, the activity is inhibited. Clearly, these outcomes require interpretations that seek us to go beyond the Fischer's lock& key mechanism and Michaelis-Menten kinetics. Please see the BBRC (2011) communication that originally reported this finding: doi.org/10.1016/j.bbrc.2011.1... and the Biochimie research article that meticulously probes the phenomenon and explains it: doi.org/10.1016/j.biochi.2016...