The EF-hand calcium (Ca^(2+)) sensor protein S100A1 combines inotropic with antiarrhythmic potency in cardiomyocytes (CM). Oxidative posttranslational modification (ox-PTM) of S100A1’s conserved, single cysteine residue (C85) via reactive nitrogen species (i.e. S-nitrosylation or glutathionylation) has been proposed to modulate conformational flexibility of intrinsically disordered sequence fragments and to increase the molecule’s affinity towards Ca^(2+). In light of the unknown …