Azure C is the product of sequential enzymatic oxidation of Metlene blue (MB) or Azure B (AB). Azure C serves as the substrate of horseradish peroxidase (HRP)[1][2].
[1]. Ferreira-LeitÃo V S, et al. Metlene blue and azure B oxidation by horseradish peroxidase: a comparative evaluation of class II and class III peroxidases. Applied Catalysis B: Environmental, 2003, 42(2): 213-221.
[2]. Lo Cascio F, et al. Azure C Targets and Modulates Toxic Tau Oligomers. ACS Chem Neurosci. 2018 Jun 20;9(6):1317-1326.