SOD activity of immobilized enzyme mimicking complexes

A binuclear, imidazolato-bridged, possible superoxide dismutase-mimicking complex (Cu(II)-diethylenetriamino-μ-imidazolato-Zn(II)-tris-aminoethylamine-triperchlorate) was prepared and immobilized on silica gel or among the layers of montmorillonite. The superoxide dismutase (SOD) activity of the complex before and after immobilization was studied by a SOD assay. It was found that the SOD activity of the host-free complex decreased somewhat when montmorillonite was the host, however, using silica gel as host it increased

Zinc and Copper Levels in Patients with Primary Hypertension and Normotension

One of the causes of primary hypertension is an exposure to free radicals. The formation of free radicals in the body can be prevented by taking antioxidants. Zinc and copper are cofactors of endogenous antioxidant enzyme superoxide dismutase. This study aimed to analyze the differences of zinc and copper levels in primary hypertensive and normotensive patients. This was an analytical observational study with cross sectional design and simple random sampling method. Subjects were patients aged 40-70 years at Haji General Hospital consisting of 15 primary hypertensive patients and 15 normotensive individuals (comparison group). Data was collected through interviews and laboratory test of blood samples. Zinc and Copper serum concentrations were measured by AAS. Data were analyzed by chi-square and independent samples t-test. The results showed that the mean levels of zinc and copper in primary hypertensive patients was lower than normotensive. However, statistically there was no difference in zinc serum levels (p=0.852) in the two groups, and there was a significant difference in copper serum levels (p=0.032). It can be concluded that there were differences in copper serum levels between the two groups but not with the levels of zinc

Paradoxical roles of antioxidant enzymes:Basic mechanisms and health implications

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated from aerobic metabolism, as a result of accidental electron leakage as well as regulated enzymatic processes. Because ROS/RNS can induce oxidative injury and act in redox signaling, enzymes metabolizing them will inherently promote either health or disease, depending on the physiological context. It is thus misleading to consider conventionally called antioxidant enzymes to be largely, if not exclusively, health protective. Because such a notion is nonetheless common, we herein attempt to rationalize why this simplistic view should be avoided. First we give an updated summary of physiological phenotypes triggered in mouse models of overexpression or knockout of major antioxidant enzymes. Subsequently, we focus on a series of striking cases that demonstrate “paradoxical” outcomes, i.e., increased fitness upon deletion of antioxidant enzymes or disease triggered by their overexpression. We elaborate mechanisms by which these phenotypes are mediated via chemical, biological, and metabolic interactions of the antioxidant enzymes with their substrates, downstream events, and cellular context. Furthermore, we propose that novel treatments of antioxidant enzyme-related human diseases may be enabled by deliberate targeting of dual roles of the pertaining enzymes. We also discuss the potential of “antioxidant” nutrients and phytochemicals, via regulating the expression or function of antioxidant enzymes, in preventing, treating, or aggravating chronic diseases. We conclude that “paradoxical” roles of antioxidant enzymes in physiology, health, and disease derive from sophisticated molecular mechanisms of redox biology and metabolic homeostasis. Simply viewing antioxidant enzymes as always being beneficial is not only conceptually misleading but also clinically hazardous if such notions underpin medical treatment protocols based on modulation of redox pathways

Structural Evidence for a Copper-Bound Carbonate Intermediate in the Peroxidase and Dismutase Activities of Superoxide Dismutase

Copper-zinc superoxide dismutase (SOD) is of fundamental importance to our understanding of oxidative damage. Its primary function is catalysing the dismutation of superoxide to O2 and H2O2. SOD also reacts with H2O2, leading to the formation of a strong copper-bound oxidant species that can either inactivate the enzyme or oxidise other substrates. In the presence of bicarbonate (or CO2) and H2O2, this peroxidase activity is enhanced and produces the carbonate radical. This freely diffusible reactive oxygen species is proposed as the agent for oxidation of large substrates that are too bulky to enter the active site. Here, we provide direct structural evidence, from a 2.15 Å resolution crystal structure, of (bi)carbonate captured at the active site of reduced SOD, consistent with the view that a bound carbonate intermediate could be formed, producing a diffusible carbonate radical upon reoxidation of copper. The bound carbonate blocks direct access of substrates to Cu(I), suggesting that an adjunct to the accepted mechanism of SOD catalysed dismutation of superoxide operates, with Cu(I) oxidation by superoxide being driven via a proton-coupled electron transfer mechanism involving the bound carbonate rather than the solvent. Carbonate is captured in a different site when SOD is oxidised, being located in the active site channel adjacent to the catalytically important Arg143. This is the probable route of diffusion from the active site following reoxidation of the copper. In this position, the carbonate is poised for re-entry into the active site and binding to the reduced copper. © 2012 Strange et al

Functional and structural mimics of superoxide dismutase enzymes

Superoxide dismutase (SOD) enzymes form important defence line in living organisms. Through a dismutation reaction they transform the highly reactive superoxide radical ion to oxygen and hydrogen peroxide. The latter compound is further transformed by catalase or peroxidase enzymes to water and oxygen. The overall structure of the enzymes and those of the active sites are largely known, thus, it has been revealed that in eukaryotes Cu(II) and Zn(II) ions act as cofactors and they are connected with an imidazolate bridge and this structural unit is coordinated with amino acids. In prokaryotes the SOD enzymes contain Mn(II) or Fe(II) or Ni(II) in their active centres. In order to learn about the working mechanism of SOD enzymes at the molecular level various structural mimics were prepared and their structural transformations during the dismutation reaction was followed. Gathering adequate amount of information allowed the preparation of functional mimics that are not necessarily copies of the active sites of the enzymes, nevertheless, display considerable SOD activity. Both functional and structural mimics are comprehensively dealt with in this review. Although enzymes may seem to be attractive catalysts for promoting real-life reactions effectively with high selectivity, they can seldom if ever be used under industrial conditions, i.e. at high temperatures and pressures. The SOD enzymes for promoting oxygen transfer reactions are not durable enough under these conditions either. The complexes mimicking SOD activities perform better in this respect, however, their reusabilities are limited, because of separation problems. A solution can be the immobilisation of these SOD mimicking complexes on solid or semi-solid supports. Even if the activity is not better then the support-free complexes, the catalyst can be filtered at the end of the reaction and can easily be recycled. Attempts for immobilisation are also comprehensively reviewed and immobilised complexes with surprisingly high SOD activities are reported as well. Full characterisation of these materials is given and rationalisation of their exceptionally high activities is offered

Amperometric enzyme sensor to check the total antioxidant capacity of several mixed berries. comparison with two other spectrophotometric and fluorimetric methods

The aim of this research was to test the correctness of response of a superoxide dismutase amperometric biosensor used for the purpose of measuring and ranking the total antioxidant capacity of several systematically analysed mixed berries. Several methods are described in the literature for determining antioxidant capacity, each culminating in the construction of an antioxidant capacity scale and each using its own unit of measurement. It was therefore endeavoured to correlate and compare the results obtained using the present amperometric biosensor method with those resulting from two other different methods for determining the total antioxidant capacity selected from among those more frequently cited in the literature. The purpose was to establish a methodological approach consisting in the simultaneous application of different methods that it would be possible to use to obtain an accurate estimation of the total antioxidant capacity of different mixed berries and the food product

The effect of vitamin C on the erythrocyte antioxidant enzymes in intoxicated-lead rat offsprings

Objective: Lead exposure or lead poisoning is known to cause a large spectrum of physiological, biochemical, and behavioural disorders in animals. This study was aimed at assessing the effect of vitamin C on the erythrocyte superoxide dismutase, glutathione peroxidase and the glutathione reductase activities in intoxicated- lead rat offsprings. Methods: This study was performed on the pups from female Wistar albino rats. The rats were divided into 4 groups and the treatments were administered through drinking water. Group1 (control group) consumed distilled water. Group 2 (lead group) consumed a solution of lead acetate (300mg/L). Group3 (lead + vitamin C) consumed a solution of lead (300mg/L) which was supplemented with vitamin C (2g/L). Group4 (vitamin group) consumed a solution of vitamin C (2g/L). The enzyme activities were determined in all the 4 groups. Results: The administration of lead showed a decrease in the enzyme activities. The superoxide dismutase activity was increased after the administration of lead in combination with vitamin C. The lead treated rats showed significantly lower body weights at birth and at weaning. The vitamin C treatment showed a significant increase in the body weight. The haemoglobin levels were significantly decreased in the lead-treated rats. The addition of vitamin C to the lead treatment and vitamin C alone could elevate the haemoglobin levels significantly. Conclusion: The results of this study showed that lead alterates the erythrocyte antioxidant enzyme activities. There was an increase in the superoxide dismutase activity following the treatment with vitamin C. This study suggests that the treatment with vitamin C during lactation has a therapeutic effect in the treatment of lead intoxication. The administration of vitamin C prevents haemoglobin reduction in the erythrocytes

Tetramerization reinforces the dimer interface of MnSOD.

Two yeast manganese superoxide dismutases (MnSOD), one from Saccharomyces cerevisiae mitochondria (ScMnSOD) and the other from Candida albicans cytosol (CaMnSODc), have most biochemical and biophysical properties in common, yet ScMnSOD is a tetramer and CaMnSODc is a dimer or "loose tetramer" in solution. Although CaMnSODc was found to crystallize as a tetramer, there is no indication from the solution properties that the functionality of CaMnSODc in vivo depends upon the formation of the tetrameric structure. To elucidate further the functional significance of MnSOD quaternary structure, wild-type and mutant forms of ScMnSOD (K182R, A183P mutant) and CaMnSODc (K184R, L185P mutant) with the substitutions at dimer interfaces were analyzed with respect to their oligomeric states and resistance to pH, heat, and denaturant. Dimeric CaMnSODc was found to be significantly more subject to thermal or denaturant-induced unfolding than tetrameric ScMnSOD. The residue substitutions at dimer interfaces caused dimeric CaMnSODc but not tetrameric ScMnSOD to dissociate into monomers. We conclude that the tetrameric assembly strongly reinforces the dimer interface, which is critical for MnSOD activity