The peroxidase—NADH biochemical oscillator: experimental system, control variables, and oxygen mass transport

The Application of Electrochemical Oscillation Methods for Identification of Traditional Chinese Medicine Materials

Electrochemical oscillation reflects the overall characteristics of the system under test in terms of redox activity. It has proven to be advantageous in analyzing and processing complex components of herbal systems, such as polysaccharides and proteins. Therefore, it is widely used in the quantitative or qualitative tests of traditional Chinese medicines (TCMs) for identification and quality control. Electrochemical oscillation has several advantages such as high sensitivity, stability and micro sample requirement. Compared with other traditional methods, the interaction of multi-component in the TCMs was taken into account, which provides new ideas for the search of TCMs. Here, we presented a brief introduction on the progress on the topic, which promoted the development of electrochemical oscillation and the standardization of TCMs in the last twenty years. Electrochemical oscillation method is cheap, sensitive, fast, stable and convenient for the identification and quality control of TCMs. Reaction systems and the visualization of the fingerprints can be improved in the future.

Effects of tyramine and 4-aminophenol on the oscillating peroxidase-oxidase reaction

The peroxidase-oxidase oscillator, a model of biological oscillations, is usually studied in conjunction with the effector molecule, 2,4-dichlorophenol. In this account, we present evidence of the effects of a naturally occurring phenol, tyramine, on the reaction, and also those of the structurally similar 4-aminophenol. Whereas 2,4-dichlorophenol gives rise to sustained oscillations at 40 μM, it was discovered that tyramine promotes damped oscillations at a concentration of 120 μM. Oxidation of NADH was completely inhibited by 4-aminophenol and ascorbate. In separate experiments, the peroxidase-catalyzed ring coupling of tyramine and 4-aminophenol was observed, which in the case of tyramine, may provide an explanation for the damping of oscillations.

Simulations of temperature sensitivity of the peroxidase-oxidase oscillator

The influence of temperature on the oscillatory kinetics of the peroxidase-oxidase reaction was studied theoretically. Assuming Q(10)=2 for elementary reactions, the effect of multiplying the rate constants of the model by factors between 0.5 and 2 (corresponding to a 10 degrees C decrease and increase, respectively, of temperature) was investigated. First, the individual rate constants were successively multiplied by 0.5 or 2 while all other rate constants were kept unchanged. This resulted in either a longer or a shorter period, depending on the rate constant being changed. Multiplication by 0.5 or by 2 generally resulted in opposite effects on the period length. However, the absolute value of this deviation differed. Also, the dynamics changed when halving the dimerization rate of NAD* as well as when doubling the rate constant for the reduction of ferric peroxidase by NAD*. Next, simulations were performed multiplying all rate constants by one and the same factor, which increased progressively from 0.5 to 2. Intervals were found corresponding to temperature dependency, compensation, and over-compensation, respectively.

Kinetic studies of the oscillatory dynamics in the peroxidase-oxidase reaction catalyzed by four different peroxidases

Oscillatory kinetics in the peroxidase-oxidase reaction catalyzed by structurally different peroxidases were investigated using NADH as a substrate. For horseradish peroxidase, lactoperoxidase, and soybean peroxidase the oscillatory waveforms of their dominating enzyme intermediates, ferric peroxidase and compound III, are similar. Coprinus peroxidase, on the other hand, has ferrous peroxidase and compound III as the dominating intermediates. The oscillatory waveform of its compound III differs from the waveforms of compound III of the three other peroxidases. Also, the phase plot of the signal for compound III versus the oxygen concentration for Coprinus peroxidase differs from the corresponding phase plots obtained using other peroxidases. A detailed model of the reaction mechanism is proposed, which is able to simulate these different kinds of behaviour. Substituting NADH with dihydroxyfumaric acid as a substrate, oscillations in the oxygen concentration were observed for about 1.5 h when a concentrated solution of this substrate was continuously fed to a solution containing horseradish peroxidase. This is the first demonstration of sustained oscillations with this substrate.

Oscillations in the peroxidase-oxidase reaction: a comparison of different peroxidases

The nonlinear behavior of the peroxidase-oxidase reaction was studied using structurally different peroxidases. For the first time sustained oscillations with peroxidases other than horseradish peroxidase in a single-enzyme system were observed. All peroxidases that showed significant oxidase activity were able to generate sustained oscillations. When adjusting the overall reaction rate, either of the two modifiers 2,4-dichlorophenol or Methylene blue could be omitted from the reaction. Due to the observation of different enzyme intermediates when using different peroxidases, we conclude that the mechanisms responsible for oscillatory kinetics may vary from one peroxidase to the other.