L name

PCL-1 probe was synthesized as described below. D-Luciferin (potassium salt) was purchased from Gold Biotechnology. H₂O₂ and HOCl were from Sigma-Aldrich. ONOO⁻ was synthesized as described elsewhere [12 (link)] and stored at −80 °C. L-NAME and DPI were from Cayman. All other chemicals were from Sigma-Aldrich and were of highest purity available. The stock solutions of ONOO⁻, HOCl and H₂O₂ were prepared freshly each day and the concentration was determined by spectrophotometry, using the extinction coefficients values of 1.7×10³ M⁻¹cm⁻¹ (at 302 nm, in 0.1 M NaOH), 350 M⁻¹cm⁻¹ (at 292 nm, in 0.1 M NaOH) and 39.4 M⁻¹cm⁻¹ (at 240 nm, in water), respectively. PCL-1 stock solution (1 mM) was typically prepared using ethanol (EtOH) as a solvent to minimize scavenging of HOCl by DMSO, a solvent typically used for boronate probes. Of the four organic solvent (EtOH, acetonitrile, DMSO and DMF) tested for interference with HOCl-induced oxidation of coumarin boronic acid (CBA) to hydroxycoumarin (COH), EtOH exhibited the smallest inhibitory effect (Suppl. Fig. 1). For the spin trapping of phenyl radical, DMSO was used to prepare the stock solution of PCL-1 to avoid scavenging of phenyl radical by EtOH. 5-Diisopropoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DIPPMPO) was synthesized according to the published procedure [20 ].

2'(3')-O-(4-Benzoylbenzoyl)adenosine 5'-triphosphate triethylammonium salt (BzATP), Adenosine 5'-diphosphate monopotassium salt dihydrate (ADP), Adenosine 5'-[β-thio]diphosphate trilithium salt] (ADPβS), N-ethylmaleimide (NEM) and tris(2-carboxyethyl)phosphine hydrochloride (TCEP) were purchased from Sigma-Aldrich (St. Louis, MO) and MRS2365 from Tocris Bioscience (Bristol, UK). 1400W, PTIO, L-NAME and Propylamine Propylamine NONOate (PAPA NONOate) were purchased from Cayman Chemical (Ann Arbor, MI). The Cx43 hemichannel mimetic peptide 43Gap26 and panx1 mimetic peptide ¹⁰panx were purchased from Anaspec (Fremont, CA).