NADH, oscillating oxidation

A number of autoxidation reactions exhibit exotic kinetic phenomena under specific experimental conditions. One of the most widely studied systems is the peroxidase-oxidase (PO) oscillator which is the only enzyme reaction showing oscillation in vitro in homogeneous stirred solution. The net reaction is the oxidation of nicotinamide adenine dinucleotide (NADH), a biologically vital coenzyme, by dioxygen in a horseradish peroxidase enzyme (HRP) catalyzed process ... 

These studies demonstrate the general mechanism of synchronization of biochemical systems, which I expect to be operative in even more complex systems, such as the mitochondrial respiration or the periodic activity of the slime mold Dictyostelium discoideum. As shown in a number of laboratories under suitable conditions mitochondrial respiration can break into self-sustained oscillations of ATP and ADP, NADH, cytochromes, and oxygen uptake as well as various ion transport and proton transport functions. It is important to note that mitochondrial respiration and oxidative phosphorylation under conditions of oscillations is open for the source, namely, oxygen, as well as with respect to a number of sink reactions producing water, carbon dioxide, and heat. 

Fig. 3.4 The glycolytic pathway produces NADH which under regular conditions is oxidized to NAD+ while reducing acetaldehyde (ACA) to ethanol (EtOH), thereby in turn reducing NAD+ in order to keep hexose catabolism running. The actual cytosolic NADH concentration is determined by the respective conversion rates of the enzymes involved in the oxidation and regeneration of the compound. If these enzymes convert additional non-natural substrates (xenobiotics, i.e. drugs), the conversion rate changes. As a consequence, the cytosolic NADH concentration differs from the natural condition. Furthermore, if a xenobiotic acts as an enzyme inhibitor, e.g. for ADH, then NAD+ regeneration is substantially affected, which eventually results in altered cytosolic NADH concentration. Therefore the presence of a xenobiotic in the cell is conceivably a perturbation factor. Under the conditions where glycolytic oscillations...

In this section we discuss the model predictions for the ketone ethyl acetoacetate (1). With the ketone absent ([Ket]x = 0 mM), the extended model reproduces all previous results with oscillations of all system variables above [Glc]xo > 18.5 mM [53]. Figure 3.6 shows the system s response to a fixed glucose concentration [Glc]xo at 30 mM and an increase of [Ket]x to 1 mM. The oscillations vanish at [Ket]x = 0.23 mM in a supercritical Hopf bifurcation and the steady state is stable for [Ket]x > 0.23 mM. Figure 3.6a shows the minimum and maximum concentrations of NADH as two thick curves, while in all other panels the time averages of the plotted variables are shown, not the minimum and maximum values. Since the addition of ketone provides an alternative mode of oxidation of NADH, the concentration of NADH is decreasing in Fig. 3.6a whereas the fluxes of carbinol production are increasing in Fig. 3.6b. 

Yamazaki and collaborators studied the horseradish peroxidase catalyzed oxidation of NADH by oxygen, 02, in an open system, and observed oscillations in concentrations of oxygen (1965) and of NADH (1967). Degn (1968, 1969) also observed oscillations in a similar peroxidase catalyzed reaction. Degn and Mayer (1969) investigated the theoretical considerations of these reactions and more recently Olsen and Degn (1977) observed chaotic oscillations in the peroxidase catalyzed oxidation of NADH by 02 in an open system, Fig. III.31. 

Fig. III.3I. Chaotic oscillations in horesradish peroxidase catalyzed oxidation of NADH by 02. Cases a), b) and c) are for decreasing concentrations of peroxidase. (From Olsen and Degn (1977))...

In analyzing oscillations in peroxidase catalyzed aerobic oxidation of NADH, Fedkina et al. (1981) experimentally obtained oscillatory results in concentrations of peroxidase compound Co(III) and 02 and NADH. They studied the influence of temperature change on the oscillations. 

Hung and Ross [6] carried out experiments in which some of the proposed tests are applied to assign roles to four of the detectable species in the HRP system oxygen, NADH, the native enzyme (Per +), and an oxidized form of the native enzyme called compound III (coIII). These tests include comparing the relative amplitude and phase shifts of the oscillations of these compounds, concentration shift regulation and destabilization experiments, qualitative pulsed species response, and quench experiments. 

Oscillatory reactions are a typical class of phenomena, which display unusual features. After the discovery of Belousov-Zhabotinskii (B-Z) reaction, there has been a tremendous flurry of activity [1] and a large number of such reactions have been discovered during recent years. Biochemical reactions [2-10] such as glycolytic oscillations and peroxidase catalysed oxidation of nicotinamide adenosine deoxyhydrogenase (NADH) have also generated considerable interest. The interest in such reactions is stiU sustained in view of their importance in understanding cardiac and neuronal oscillations. In the case of many oscillatory chemical reactions [1], detailed reaction mechanisms have been postulated and verified with the help of numerical computation. This has also been particularly so for B-Z reaction where Field-Koros-Noyes (FKN) mechanism [11] has been invoked. 

Among the many systems Racker used, one is a particulate system prepared by exposing beef mitochondria to sonic oscillation. The system can oxidize succinate and NADH but cannot couple the oxidation of the substrate to the phosphorylation of ADP. Coupling can be achieved by adding to the system two soluble proteins referred to by Racker as factor 1 (FJ and factor 4 (F4). F is a protein with ATPase activity obtained by sonic disintegration of mitochondria. F4 is prepared by alkaline extraction of the mitochondria. Fi, which has been extensively purified, is a decamer with a molecular weight of 284,000, each monomer weighing 26,000. 

Oscillating chemiluminescence has been observed in the H2O2/KSCN/ CuS04/NaOH/luminol system there are two types of oscillation, and the low-intensity mode may involve the reaction of superoxide with luminol. A simplified mechanism for the methylene-blue/HS /02 oscillation in a CSTR has been proposed. Experimental and modeling structures of oscillation in the C102/l2/malonic acid system show that the oscillations are not due to autocatalysis but to self-inhibition in the ClOf/I reaction. A study of the oxidation of hexacyanoferrate(II) by bromine is concluded to involve the formation of Brf as an intermediate, formed in the first step. The aerobic oxidation of NADH catalyzed by horse radish peroxidase... 

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