Electron-transfer reactions oxidase

Bilirubin oxidase, 603-606, 621-626 Biomimetic catalysts, 679-686 Bond-breaking electron transfer reactions, 43-44... 

L. Jiang, C.J. McNeil, and J.M. Cooper, Direct electron transfer reaction of glucose oxidase immobilized at a self-assembled monolayer. J. Chem. Soc. Chem. Commun. 1293-1295 (1995). 

Cytochrome c is responsible for accepting an electron from cytochrome Ci and transferring it to cytochrome c oxidase. The electron transfer reaction may occur via the exposed portion of the ring or by tunnelling through the protein (and involving an outer-sphere mechanism). The details of this process have not been fully elucidated and have remained the focus of much research. 

If XO is an undoubted historical pioneer among free radical-producing enzymes, whose capacity to catalyze one-electron transfer reactions opened a new era in biological free radical studies, NADPH oxidase is undoubtedly the most important superoxide producer. This enzyme possesses numerous functions from the initiation of phagocytosis to cell signaling, and it is not surprising that its properties have been considered in many reviews during last 20 years [56-58]. 

Parr, S. R., Barber, D., Greenwood, C., and Brunori, M. (1977). The electron-transfer reaction between azurin and the cytochrome c oxidase from Pseudomonas aeruginosa. Biochem. J. 167, 447-455. 

The heme groups of the cytochromes as well as many other transition metal centers act as carriers of electrons. For example, cytochrome c may accept an electron from reduced cytochrome Cj and pass it to cytochrome oxidase or cytochrome c peroxidase. The electron moves from one heme group to another over distances as great as 2 nm. Similar electron-transfer reactions between defined redox sites are met in photosynthetic reaction centers (Fig. 23-31), in metalloflavo-proteins (Fig. 15-9), and in mitochondrial membranes. 

Redox potentials of the molybdenum centers in several of the enzymes have been obtained by potentiometric titration (Table 3a). Although the substrate reaction chemistry requires the metal center to participate in net two-electron redox reactions, the simple electron-transfer reactions of the active sites occur in one-electron steps involving the MoVI/Mov and Mov/MoIV couples. Several of the molybdenum enzymes studied have MoVI/Mov and Mov/MoIV couples that differ by less than 40 mV. However, in sulfite oxidase the Movl/Mov (38 mV) and Mov/Molv (-239 mV) couples are separated by roughly 275 mV [88], In formate dehydrogenase (D. desulfuricans) the MoVI/Mov (-160 mV) and Mov/MoIV (-330 mV) couples are separated by 170 mV [89], Both the MoVI/Mov and... 

Galactose oxidase is an extracellular enzyme secreted by the fungus Dactylium den-droides. It is monomeric (M = 68000), contains a single copper site and catalyses the oxidation of a wide range of primary alcohols to the corresponding aldehydes. The two-electron transfer reaction RCH2OH - RCHO + 2H+ + 2e does not utilise a Cu(III)/Cu(I) couple, but a second redox site, involving a tyrosine radical which mediates the transfer of the second electron. 

At first, a two-electron transfer reaction took place between gold and the glucose oxidase. However, as time (in terms of minutes) went on, the electrodic response (Fig. 

Cytochrome c, a small heme protein (mol wt 12,400) is an important member of the mitochondrial respiratory chain. In this chain it assists in the transport of electrons from organic substrates to oxygen. In the course of this electron transport the iron atom of the cytochrome is alternately oxidized and reduced. Oxidation-reduction reactions are thus intimately related to the function of cytochrome c, and its electron transfer reactions have therefore been extensively studied. The reagents used to probe its redox activity range from hydrated electrons (I, 2, 3) and hydrogen atoms (4) to the complicated oxidase (5, 6, 7, 8) and reductase (9, 10, 11) systems. This chapter is concerned with the reactions of cytochrome c with transition metal complexes and metalloproteins and with the electron transfer mechanisms implicated by these studies. 

The substrate half-reactions are displayed in Tables I and II. In each case, a two-electron process seems to be involved. Only in nitro-genase are greater numbers of electrons transferred, and the discussion earlier in this paper summarizes the evidence that these processes occur in two-electron steps. The two-electron reaction of the molybdenum site never appears to be simply an electron transfer reaction. In the case of nitrogenase, each substrate takes up an equal (or greater) number of protons to form the product. In the other molybdenum enzymes, proton transfer and addition or removal of H20 are also required. In each case, however, there is at least one proton transferred in the same direction as the pair of electrons. These data, taken in conjunction with the EPR evidence for proton transfer from the substrate to the active site in xanthine oxidase, suggest that the molybdenum site in all the enzymes... 

Hill, B. C., 1994, Modeling the sequence of electron transfer reactions in the single turnover of reduced, mammalian cytochrome c oxidase with oxygen, J. Biol. Chem. 269 2419n2425. 

Copper Hemocyanrn/Tyrosinase Models Copper Proteins with Dinuclear Active Sites Copper Proteins with Type 1 Sites Copper Proteins with Type 2 Sites Cytochrome Oxidase Electron Transfer Reactions Theory Long-range Electron Transfer in Biology Metal Ion Toxicity Metal-related Diseases of Genetic Origin Metallochaperones Metal Ion Homeostasis Nutritional Aspects of Metals Trace Elements. 

Copper Proteins with Type 1 Sites Cytochrome Oxidase Electron Transfer in Coordination Compounds Electron Transfer Reactions Theory Iron Heme Proteins Electron Transport Iron Heme Proteins, Peroxidases, Catalases Catalase-peroxidases Photosynthesis. 

Despite all these structural studies the physiological function of amavadine in mushrooms is still elusive. A suggestion has been made (106) that it may act as a cofactor with a protective oxidase or peroxidase function. On the other hand, the electrochemistry (111) of amavadine is such that it may have a role in electron-transfer reactions involving the vanadium(V)/(IV) redox couple. 

Electron-transfer reactions of amines are of significant importance in biochemical systems. Enzymes known to catalyze the oxidative dealkylation of amines include monoamine oxidase [16, 17], cytochrome-P450 [18, 184-186], horseradish peroxidase [187], hemoproteins [188, 189], and chloroperoxidase [187, 188]. N-dealkylation of amines by peroxidases are generally accepted to occur via one-electron transfer, whereas the role of electron transfer in reactions catalyzed by enzymes such as monoamine oxidase [16, 17] and cytochrome P-450 [18, 184, 185] is currently a topic of debate. 

---