Hypocrates sensitivity and reaction rates.Changes in the fluorescence excitation spectra of Hypocrates (0.5 µM) obtained by additions of a NaOCl or b N-chlorotaurine (NCT) aliquots. c Titration curves of Hypocrates (0.5 µM) in sodium phosphate buffer obtained by additions of NaOCl, NaOBr, HOSCN, or NCT aliquots. The data are presented as a mean ± SEM (for n > 2), n ≥ 2. The maximum amplitudes of response are 2.0-, 1.8-, 1.8- and 1.7-fold for NaOBr, HOSCN, NaOCl, and NCT, respectively. In the presence of NaOBr, NaOCl, and NCT, the probe is saturated at ~5 µM, and for HOSCN at ~1 µM. d The same data as in c, Hypocrates sensitivity towards NaOCl, NaOBr, NCT, and HOSCN is shown. The data are presented as a mean ± SEM (for n > 2), n ≥ 2. e–g Hypocrates reaction rates. Changes in cpYFP fluorescence at > 515 nm cut-off (λex = 485 nm) were measured as a function of time (insert). The curves were fitted to a double exponential to obtain the observed rate constants (kobs/fast), which were plotted as a function of different e NaOCl, f NCT, or g NaOBr concentrations. The second-order rate constants for NaOCl (1.4 ± 0.056) × 106 M−1s−1, NCT (6.1 ± 0.3) × 104 M−1s−1, and NaOBr (4.5 ± 0.25) × 106 M−1s−1 were determined from the slope of the straight line [kfast = kon⋅[oxidant] + koff]. The data are presented as a mean ± SD (for n > 2), n ≥ 2. Source data are provided as a Source Data file.