Superoxide types

In conclusion, it is noted that, as an empirical rule, first row transition metal elements generally form superoxide-type dioxygen complexes, whereas elements of the second and third transition series form peroxide-type dioxygen complexes. 

Finally, a series of complexes in which dioxygen is weakly bound to the metal have been used as models for biological oxygen transport.166 a,b The mode of bonding of the 02 group in compound VII is bent, with a Co—O—O bond angle of 153°. The complex may be formulated as a low-spin octahedral Co(III) complex of the superoxide ion, 02 Electron spin resonance studies of other Schiff base and porphyrin complexes also support superoxide-type structures.166b... 

Here A is the starting compound, B is the product, X is the superoxide type molecules or radicals, and Y means the aldehyde type molecules or radicals. One can see that the scheme postulates an autocatalysis with the two intermediates. Let s assume the reagent concentration does not depend on time (A = const), i.e. its consumption rate is compensated by its insertion into the reactor. That will give us the following equation set ... 

They are typical of metals with the d - (Ir Co" and d - (Pt , Pd , Ni ) configurations with electron-donor, e.g., phosphorus, ligands and ligands of the superoxide type... 

Figure 14.4 The four main types of O2-M geometry. The bridging modes Ib and lib appear superficially similar but differ markedly in dihedral angles and other bonding properties. See also footnote to Table 14.5 for the recently established unique /Lt.rj -superoxide bridging mode.

Shimomura, O., Wu, C., Murai, A., and Nakamura, H. (1998). Evaluation of five imidazopyrazinone-type chemiluminescent superoxide probes and their application to the measurement of superoxide anion generated by Listeria monocytogenes. Anal. Biochem. 258 230-235. 

On the other hand. Type II process competes efficiently with the electron-transfer pathway in aerobic environments where the concentration of ground triplet state molecular oxygen is relatively high ( 0.27 mM), and singlet molecular oxygen (1O2) is the most abimdant ROS generated under these conditions, with a quantum yield 0.48 (Valle et al., 2011), eqn. 8. It is also possible an electron-transfer reaction from 3RF to 02 to form anion superoxide, but this reaction occurs with very low efficiency <0.1% (Lu et al., 2000). 

Superoxide is formed (reaction 1) in the red blood cell by the auto-oxidation of hemoglobin to methemo-globin (approximately 3% of hemoglobin in human red blood cells has been calculated to auto-oxidize per day) in other tissues, it is formed by the action of enzymes such as cytochrome P450 reductase and xanthine oxidase. When stimulated by contact with bacteria, neutrophils exhibit a respiratory burst (see below) and produce superoxide in a reaction catalyzed by NADPH oxidase (reaction 2). Superoxide spontaneously dismu-tates to form H2O2 and O2 however, the rate of this same reaction is speeded up tremendously by the action of the enzyme superoxide dismutase (reaction 3). Hydrogen peroxide is subject to a number of fates. The enzyme catalase, present in many types of cells, converts... 

Interest in superoxide dismutase has increased in recent years with the discovery that a mutation in the gene coding for SOD is linked to certain types of the neurodegenerative disease amyotrophic lateral sclerosis (ALS), commonly known as Lou Gehrig s disease. Exactly how mutant forms of SOD are involved in ALS is a subject of intense research. 

Type 11 are 02-sensitive two-electron reductases that catalyze the reduction to ArN02 radicals that react with O2 to produce superoxide (Bryant and DeLuca 1991 Bryant et al. 1991). 

Wuerges J, J-W Lee, Y-I Yim, H-S Yrm, S-O Kang, KD Carugo (2004) Crystal structure of nickel-containing superoxide dismutase reveals another type of active site. Proc Natl Acad Sci USA 101 8569-8574. 

Superoxide dismutases (SODs) are a family of cytosolic metalloenzymes that specifically remove (reviewed by Omar etal., 1992). SOD distribution within the body is ubiquitous, being found in erythrocytes as well as most organs and cell types. Three distinct mammalian SOD forms exist CuZnSOD, MnSOD and extracellular SOD (EC-SOD). Their amino-acid sequences differ as well as the transition metals at their active sites. Rheumatoid synovial fluid contains low levels of SOD activity and hence little protection from ROM generated by infiltrating PMNs (Blake etcU., 1981). Furthermore, leucocytes from patients with RA are deficient in MnSOD, which might promote the extracellular leakage of O2 (Pasquier et al., 1984). 

Collier et al. (1990) extended their studies relating to oxidative stress and diabetes by demonstrating that the levels of several free-radical scavengers (red cell superoxide dismutase, plasma thiols) were significantly reduced in 22 type 2 diabetic patients (mean age 53 years) in comparison with 15 control subjects (mean age 51 years). No significant diflFerences in red cell lysate thiols or... 

Figure 12.2 Copper chaperone function, (a) Copper homeostasis in Enterococcus hirae is affected by the proteins encoded by the cop operon. CopA, Cu1+-import ATPase CopB, Cu1+-export ATPase CopY, Cu1+-responsive repressor copZ, chaperone for Cu1+ delivery to CopY. (b) The CTR family of proteins transports copper into yeast cells. Atxlp delivers copper to the CPx-type ATPases located in the post Golgi apparatus for the maturation of Fet3p. (c) Coxl7p delivers copper to the mitochondrial intermembrane space for incorporation into cytochrome c oxidase (CCO). (d) hCTR, a human homologue of CTR, mediates copper-ion uptake into human cells. CCS delivers copper to cytoplasmic Cu/Zn superoxide dismutase (SOD1). Abbreviations IMM, inner mitochondrial membrane OMM, outer mitochondrial membrane PM, plasma membrane PGV, post Golgi vessel. Reprinted from Harrison et al., 2000. Copyright (2000), with permission from Elsevier Science.

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