Oxidase/peroxidase reaction

The existence of chaotic oscillations has been documented in a variety of chemical systems. Some of tire earliest observations of chemical chaos have been on biochemical systems like tire peroxidase-oxidase reaction [12] and on tire well known Belousov-Zhabotinskii (BZ) [13] reaction. The BZ reaction is tire Ce-ion-catalyzed oxidation of citric or malonic acid by bromate ion. Early investigations of the BZ reaction used tire teclmiques of dynamical systems tlieory outlined above to document tire existence of chaos in tliis reaction. Apparent chaos in tire BZ reaction was found by Hudson et a] [14] aiid tire data were analysed by Tomita and Tsuda [15] using a return-map metliod. Chaos was confinned in tire BZ reaction carried out in a CSTR by Roux et a] [16, E7] and by Hudson and... 

C.G.Steinmetz, T.Geest and R.Larter, Universality in the Peroxidase-Oxidase Reaction Period Doubling, Chaos, Period Three, and Unstable Limit Cycles, The Journal of Physical Chemistry, 97, 5649-5653(1993). 

C.G.Steimnetz and R.Larter, The Quasiperiodic Route to Chaos in a Model of the Peroxidase-Oxidase Reaction, Journal of Chemical Physics, 94, 1388-1396(1991). 

No cofactors have been reported in the tryptophan peroxidase-oxidase reaction, but the marked reduction in the conversion of tryptophan to nicotinic acid in thiamine deficiency has been found in all probability to be due to interference with the reaction at the tryptophan peroxidase-oxidase stage (173 c/. diagram 19). The evidence is still inadequate to show how enzyme function and vitamin are related. Biotin may also be concerned in the reaction (800 but see 175a). 

Besides the ordinary HoO -consuming oxidation, peroxidase also catalyzes Oo-consuming oxidation (the peroxidase-oxidase reaction). In recent years considerable attention has been directed to elucidating the peroxidase-oxidase mechanism. Controversy was centered about the participation of ferrous enzyme in O2 activation. Is peroxidase reduced to the ferrous state during the reaction 3,13,19, 21, 23) Does peroxidase compound III, which appears in the reaction, correspond to oxygenated ferroperoxidase (3, 5, 15) If so, is O2 in Compound III activated (15) As discussed here, these problems seem to be almost solved, and it is very likely that the peroxidase-oxidase reaction is a good model for analyzing the mechanism of other oxidases. 

We have never succeeded in detecting by ESR the free radicals of important biological molcules such as lAA (indoleacetic acid) and NADH which are substrates for the peroxidase-oxidase reaction. When an electron acceptor such as ferric ion with o-phenanthroline is added to the peroxidase system, one can observe the stoichiometric reduction of iron (Figure 2) described in the following reactions (28). 

Figure 5. Chain mechanism in the peroxidase-oxidase reaction. The mechanism can explain the majority of O. -coiisuming oxidations of various electron donors catalyzed hy peroxida.ses...

O2 Activation by the Ferrous Enzyme. Reduction of Peroxidase. The great controversy over the peroxidase-oxidase reaction has centered about the participation of the ferrous enzyme. We pointed out the possibility of a partial contribution of the ferrous enzyme, especially when lAA or NADH was used as a hydrogen donor (32). Although it is still impossible to detect the semiquinones of these molecules by ESR, it may be concluded from the stoichiometric results of Reactions 11 and 12 that H2O2 produces two semiquinone molecules of lAA and NADH. When excess peroxidase rather than the added acceptors is present, peroxidase itself will be reduced by the semiquinones. Ferroperoxidase can be ob-seiwed easily even in the absence of CO when NADH is used as donor (33). The semioxidized lAA molecule seems to have unusual reactivity... 

Figure 7. Tentative scheme for the relationship between peroxidase compounds which appear during the peroxidase-oxidase reactions...

Figure 11 shows the mechanism of 0. activation caused by introducing a single electron into the system. The sources of such an electron may be a key point in certain Oj-activating enzymes. For the peroxidase system, they are free radicals of electron donors, as shown by a series of ESR experiments (29, 30). A strong single-equivalent oxidant produces a powerful reductant in the two-equivalent system. In the peroxidase-oxidase reaction the reductant is used for direct reduction of O2 or formation of ferrous enzyme. The peroxidase-oxidase reaction has mixed... 

Aguda, B.D., L.L. Hofmann-Frisch L.F. Olsen. 1990. Experimental evidence for the coexistence of oscillatory and steady states in the peroxidase-oxidase reaction. J. Am. Chem. Soc. 112 6652-6. 

Olsen, L.F. 1978. The oscillating peroxidase-oxidase reaction in an open system Analysis of the reaction mechanism. Biochim. Biophys. Acta 527 212-20. 

Olsen, L.F. 1979. Studies of the chaotic behaviour in the peroxidase-oxidase reaction. Z. Naturforsch. 34a 1544-6. 

Let us illustrate this technique with the results of simulated measurements of the peroxidase-oxidase reaction based on a skeleton model proposed by Degn et al. [51] (the DOP model). There are four species involved in the model Si = O2, S2 = NADH, S3 and S4 are intermediates associated according to Olsen et al. [52] with free radical... 

Table 11.3 Sign-symbolic phase shift matrix obtained from the DOP model of the peroxidase-oxidase reaction...

Hung, Y.-F. Ross, J. New experimental methods toward the dednction of the mechanism of the oscillatory peroxidase oxidase reaction. J. Phys. Chem. 1995, 99, 1974—1979. 

Steinmetz, C. G Geest, T. Barter, R. Universality in the peroxidase oxidase reaction— period doublings, chaos, period 3, and unstable limit cycles. J. Phys. Chem. 1993, 97, 5649-5653. 

Aguda, B. Clarke, B. L. Bistability in chemical reaction networks—theory and application to the peroxidase-oxidase reaction. J. Chem. Phys. 1987, 87, 3461-3470. 

Rgnre 29 A circle map derived from simulations with the DOP model of die peroxidase-oxidase reaction. (From Ref. 73 used with permission.)... 

A studyof a fairly simple model of an enzyme reaaion that exhibits chaotic behavior, the peroxidase-oxidase reaction, provides a good illustration of the role of circle map dynamics and mixed-mode oscillations in the transition to chaos. In the peroxidase-oxidase reaction, the peroxidase enzyme from horseradish (which, as its name implies, normally utilizes hydrogen peroxide as the electron acceptor) catalyzes an aerobic oxidation... 

Figure 33 Evolution of a torus attractor found in simulations with the DOP model of the peroxidase-oxidase reaction, equations [115]. Parameter values used are k2 = 1250, fea = 0.046875, = 1. 104, = 0.001,...

This example shows that mixed-mode oscillations, while arising from a torus attractor that bifurcates to a fractal torus, give rise to chaos via the familiar period-doubling cascade in which the period becomes infinite and the chaotic orbit consists of an infinite number of unstable periodic orbits. Mixedmode oscillations have been found experimentally in the Belousov-Zhabotin-skii (BZ) reaction 2.84 and other chemical oscillators and in electrochemical systems, as well. Studies of a three-variable autocatalator model have also provided insights into the relationship between period-doubling and mixedmode sequences. Whereas experiments on the peroxidase-oxidase reaction have not been carried out to determine whether the route to chaos exemplified by the DOP model occurs experimentally, the DOP simulations exhibit a route to chaos that is probably widespread in the realm of nonlinear systems and is, therefore, quite possible in the peroxidase reaction, as well. 

An example of a calculation of the Lyapunov exponents and dimension, for a simple four-variable model of the peroxidase-oxidase reaction will help to clarify these general definitions. The following material is adapted from the presentation in Ref. 94. As described earlier, the Lyapunov dimension and the correlation dimension, D, serve as upper and lower bounds, respectively, to the fractal dimension of the strange attractor. The simple four-variable model is similar to the Degn—Olsen-Ferram (DOP) model discussed in a previous section but was suggested by L. F. Olsen a few years after the DOP model was introduced. It remains the simplest model the peroxidase-oxidase reaction which is consistent with the most experimental observations about this reaction. The rate equations for this model are ... 

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