Oxidation state monooxygenase

The conversion of hydroperoxide/peroxide to superoxide is a one-electron redox reaction and requires the presence of transition metals having accessible multiple oxidation states as in biological iron or manganese clusters (e.g., Fe(II, III, IV) clusters of monooxygenase or the Mn(II, HI, IV) clusters of photosystems). Ti is usually not reduced at ambient temperatures. The various possibilities that could facilitate the transformation of hydroperoxo/peroxo to superoxo species are as follows ... 

Other than for the monooxygenases, a two-electron acceptor such as hydrogen peroxide is required as the terminal oxidant for peroxidases. In the so-called resting state the Fe ion is situated in the oxidation state +3. Reaction with hydrogen peroxide proceeds with loss of water and yields a ferryl(IV) radical cation called Compound I,... 

Rosenzweig, A. C., Nordlund, P., Takahara, P. M., Frederick, C. A., and Lippard, S. J., 1995, Geometry of the soluble methane monooxygenase catalytic diiron center in two oxidation states, Chem. Biol. 2 4099418. 

The cytochrome P-450 monooxygenase system. P-4503+ Cytochrome P-450 with heme iron in oxidized state (Fe3+) P-45021 cytochrome P-450 with iron in reduced state S substrate e electron. (Adapted from J. A. Trimbell, 1982. Principles of Biochemical Toxicology. Taylor Francis, London.)... 

Vanadium is an element, and as such, is not metabolized. However, in the body, there is an interconversion of two oxidation states of vanadium, the tetravalent form, vanadyl (V+4), and the pentavalent form, vanadate (V+5). Vanadium can reversibly bind to transferrin protein in the blood and then be taken up into erythrocytes. These two factors may affect the biphasic clearance of vanadium that occurs in the blood. Vanadate is considered more toxic than vanadyl, because vanadate is reactive with a number of enzymes and is a potent inhibitor of the Na+K+-ATPase of plasma membranes (Harris et al. 1984 Patterson et al. 1986). There is a slower uptake of vanadyl into erythrocytes compared to the vanadate form. Five minutes after an intravenous administration of radiolabeled vanadate or vandadyl in dogs, 30% of the vanadate dose and 12% of the vanadyl dose is found in erythrocytes (Harris et al. 1984). It is suggested that this difference in uptake is due to the time required for the vanadyl form to be oxidized to vanadate. When V+4 or V+5 is administered intravenously, a balance is reached in which vanadium moves in and out of the cells at a rate that is comparable to the rate of vanadium removal from the blood (Harris et al. 1984). Initially, vanadyl leaves the blood more rapidly than vandate, possibly due to the slower uptake of vanadyl into cells (Harris et al. 1984). Five hours after administration, blood clearance is essentially identical for the two forms. A decrease in glutathione, NADPH, and NADH occurs within an hour after intraperitoneal injection of sodium vanadate in mice (Bruech et al. 1984). It is believed that vanadate requires these cytochrome P-450 components for oxidation to the vanadyl form. A consequence of this action is the diversion of electrons from the monooxygenase system resulting in the inhibition of drug dealkylation (Bruech et al. 1984). 

The two-electron reduction of the diferric forms of hemerythrin (51), ribonucleotide reductase (27, 50), and methane monooxygenase (31) yields dioxygen-sensitive diferrous forms of the proteins. All three can be generated by dithionite treatment of the corresponding diferric forms, although the RRB2 reduction requires methyl viologen as mediator. The Fe(II) oxidation state is more difficult to probe spectroscopically, and only recently have methods been developed that allow this state to be characterized further. 

Biomimetic studies are currently focused on generating diiron complexes that can serve as structural and/or electronic models for oxidation states higher than Fe " that are proposed to partake in the catalytic cycles of diiron proteins such as methane monooxygenase and ribonucleotide reductase. Mossbauer spectroscopy has played a leading role in the eharacterization... 

Figure 4 Active site structures and corresponding oxidation states for iron-oxo dimer proteins methane monooxygenase (MMOH) ribonucleotide reductase (RNR) and hemerythrin (Hr).

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