Respiratory O2 reduction

RESPIRATORY O2 REDUCTION CATALYSIS 18.2.1 Basic Aspects of Energy Metabolism... 

Boulatov R. 2004. Understanding the reaction that powers this world Biomimetic studies of respiratory O2 reduction by cytochrome oxidase. Pure Appl Chem 76 303. 

Cyanide is a potent respiratory inhibitor that is much more reactive with Fe + than with Fe +. Thus, this reagent has compensated for CO, which lacks reactivity to Fe +, in studies of the function of the O2 reduction site, since the historical work of Keilin and Hartree (1938b) for identihcation of hemes a and as. However, cyanide is reactive also to ferrous iron although much more weakly than to ferric iron. Among... 

The dual physiological role of HCOs determines the energetics of O2 reduction by these enzymes (reactions 1.8-1.13, Figure 1.8). By clearing the respiratory electron transfer chain from low-potential (weakly reducing) electron CcOs... 

Figure 18.2 Summary of respiratory energy flows. Foods ate converted into the reduced form of nicotinamide adenine dinucleotide (NADH), a strong reductant, which is the most reducing of the respiratory electron carriers (donors). Respiration can he based on a variety of terminal oxidants, such as O2, nitrate, or fumarate. Of those, O2 is the strongest, so that aerobic respiration extracts the largest amount of free energy from a given amount of food. In aerobic respiration, NADH is not oxidized directly by O2 rather, the reaction proceeds through intermediate electron carriers, such as the quinone/quinol couple and cytochrome c. The most efficient respiratory pathway is based on oxidation of ferrocytochrome c (Fe ) with O2 catalyzed by cytochrome c oxidase (CcO). Of the 550 mV difference between the standard potentials of c)Tochrome c and O2, CcO converts 450 mV into proton-motive force (see the text for further details).

The reduction of ground state O2 with organic substances is fairly slow in aqueous or nonaqueous solutions [57] in spite of the high redox potential of O2. The O2 is utilized effectively, however, as the terminal oxidant in the respiratory chain in a biomembrane with redox enzymes composed of membrane proteins such as heme proteins containing cytochrome c oxidase [58-60] or quinol oxidase [61,62]. 

Because electrode measurements of O2 uptake can detect intra- and extracellular oxidase activity, this assay can be used to measure the respiratory burst elicited by soluble and particulate stimuli. What is somewhat surprising is that, during stimulation of neutrophils with agonists such as fMet-Leu-Phe, the activated O2 uptake profile is biphasic (Fig. 5.11c). A rapid burst of O2 uptake (which coincides with measurements of cytochrome c reduction) is followed by a more sustained activity of lower magnitude. 

The demonstration that PMNs formed O2- in the respiratory burst necessitated the consideration of all the species which result when dioxygen is reduced one electron at a time (Fig. 1). Superoxide, the result of the reduction of dioxygen by one electron, appears to act mainly as a mild reductant in aqueous solutions. But when it coexists with H2O2, its spontaneous dismutation product, O can initiate a number of potentially injurious events [reviewed by Fridovich The primary means by which cells deal with superoxide anions appears to be through the catalysis of their dismutation by a family of metalloenzymes collectively designated superoxide dismutases. 

Time until respiratory arrest [min] Inhaled volume of 1,000 victims [m3] in free volumes of the room Reduction of o2 content (30% Reduction of o2 content (20%... 

Respiration, electrochemical aspects — The function of the enzymes in the mitochondrial respiratory chain is to transform the energy from the redox reactions into an electrochemical proton gradient across the hydrophobic barrier of a coupling membrane. Cytochrome oxidase (EC 1.9.3.1, PDB 20CC) is the terminal electron acceptor of the mitochondrial respiratory chain. Its main function is to catalyze the reaction of oxygen reduction to water using electrons from ferrocytochrome c 4H+ + O2 + 4e 2H2O. Cytochrome oxidases can trans-... 

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