On the role of methylene blue in the oscillating peroxidase–oxidase reaction

Melatonin Activates the Peroxidase–Oxidase Reaction and Promotes Oscillations

“…Immediately following this decrease the reaction starts to oscillate. The concentration of per 2ϩ remains low throughout the experiment, due to the presence of MB, since even small amounts of MB inhibit reduction of per 3ϩ to per 2ϩ (16). We observed similar stimulation of the PO reaction catalyzed by other peroxidases such as LPO and SBP.…”

“…The molar extinction coefficients used in the calculations of c for NADH and the three enzyme intermediates of horseradish peroxidase (16,17) are listed in Table 1, while those obtained for lactoperoxidase (17) are listed in Table 2.…”

“…The rate of oxygen diffusion V O2 into the liquid is given by the equation [2] where We recorded the time series of the absorbencies in the range 350 -600 nm (1 nm resolution) and the O 2 concentration in the liquid every 2 s and stored the data on a computer for later analysis. Specifically the absorbencies at wavelengths corresponding to NADH, ferric peroxidase (per 3ϩ ), compound III and ferrous peroxidase (per 2ϩ ) were used for spectral deconvolution of the absorbance measurements to concentrations of these four species (16). Their concentrations were determined by solving the system of linear equations…”

Oxidase–peroxidase reaction: kinetics of peroxidase-catalysed oxidation of 2-aminophenol

“…Literature data referring to HRP inactivation during the oxidation of specific reducing substrates (NADH, fumaric acid, indole-3 acetic acid) with di-oxygen/hydrogen peroxide [18,[21][22][23]42] report the formation of low-reactive species Compound III, which does not participate in the normal peroxidase cycle, but it was found reactive enough to oxidize phenols [10,17,25,30]. There are several possible pathways of Compound III formation [34][35][36]42], whose occurrences in the present experiment will be further investigated (Scheme 5).…”

“…Peroxidase is unable to react directly with oxygen, but its reduced form, ferrous peroxidase reacts with oxygen to form Compound III [22]. NADH and indole-3-acetic acid are some of the few substrates that activate both oxidase and peroxidase cycles [23][24][25]. Due to the possibility to follow two catalytic cycles, peroxidases can react with reactive oxygen species (ROS) [26,27].…”