ASMI

Biochem/physiol Actions

ASMI is a cell-permeable, non-toxic, biocompatible, photostable, positively charged, mitochondria targeting styryl-methylpyridinium based compound that acts as a rapid, cysteine selective, sensitive, and ratiometric (F 518 /F 452 ?nm) fluorescent turn-on probe (0.5 - 40 μM of [Cys]). Under physiological conditions, cysteine thiol reacts with the ASMI acrylate moiety in a time-dependent manner, and induces a facile intramolecular cyclization to release fluorogenic oxystyryl methylpyridinium. ASMI displays high selectivity over other biothiols (Kobs??= 0.75, 0.038, 0.011 & 0.012 min -1 ?for Cys, Hcy, GSH & Na 2 S, respectively) and with no interference from other biologically relevant amino acids, essential metal ions, and anions, including Na2S. Shown to monitor mitochondrial Cys levels in HeLa cells and in deep tissues (150 μm of penetration depth) by two-photon excited fluorescence microscopy.