Release Of Iron Ions Research Articles

Generation of hydroxyl radicals by soybean nodule leghaemoglobin

Leghaemoglobin, a protein present in root nodules of soybean (Glycine max (L.) Merr.), generates the highly reactive hydroxyl radical (·OH) upon incubation with hydrogen peroxide (H2O2). The H2O2 appears to cause breakdown of the haem, releasing iron ions that convert H2O2 into ·OH outside the protein. Oxyleghaemoglobin (oxygenated ferrous protein) is more sensitive to attack by H2O2 than is metleghaemoglobin (ferric protein). The possibility of oxyleghaemoglobin breakdown by H2O2 and formation of damaging ·OH may explain why the root nodule is equipped with iron-storage proteins and enzymes that can remove H2O2.

Formation of hydroxyl radicals in biological systems. Does myoglobin stimulate hydroxyl radical formation from hydrogen peroxide?

Incubation of horse-heart oxymyoglobin or metmyoglobin with excess H2O2 causes formation of myoglobin(IV), followed by haem degradation. At the time when haem degradation is observed, hydroxyl radicals (.OH) can be detected in the reaction mixture by their ability to degrade the sugar deoxyribose. Detection of hydroxyl radicals can be decreased by transferrin or by .OH scavengers (mannitol, arginine, phenylalanine) but not by urea. Neither transferrin nor any of these scavengers inhibit the haem degradation. It is concluded that intact oxymyoglobin or metmyoglobin molecules do not react with H2O2 to form .OH detectable by deoxyribose, but that H2O2 eventually leads to release of iron ions from the proteins. These released iron ions can react to form .OH outside the protein or close to its surface. Salicylate and the iron chelator desferrioxamine stabilize myoglobin and prevent haem degradation. The biological importance of .OH generated using iron ions released from myoglobin by H2O2 is discussed in relation to myocardial reoxygenation injury.

Formation of hydroxyl radicals from hydrogen peroxide in the presence of iron. Is haemoglobin a biological Fenton reagent?

The ability of oxyhaemoglobin and methaemoglobin to generate hydroxyl radicals (OH.) from H2O2 has been investigated using deoxyribose and phenylalanine as 'detector molecules' for OH.. An excess of H2O2 degrades methaemoglobin, releasing iron ions that react with H2O2 to form a species that appears to be OH.. Oxyhaemoglobin reacts with low concentrations of H2O2 to form a 'reactive species' that degrades deoxyribose but does not hydroxylate phenylalanine. This 'reactive species' is less amenable to scavenging by certain scavengers (salicylate, phenylalanine, arginine) than is OH., but it appears more reactive than OH. is to others (Hepes, urea). The ability of haemoglobin to generate not only this 'reactive species', but also OH. in the presence of H2O2 may account for the damaging effects of free haemoglobin in the brain, the eye, and at sites of inflammation.

The stimulatory effects of asbestos on NADPH-dependent lipid peroxidation in rat liver microsomes.

Lipid peroxidation in rat liver microsomes induced by asbestos fibres, crocidolite and chrysotile, is greatly increased in the presence of NADPH, leading to malondialdehyde levels comparable with those induced by CCl4, a very strong inducer of lipid peroxidation. This synergic effect only occurs during the first minutes and could be explained by an increase or a regeneration of the ferrous active sites of asbestos by NADPH, which in turn could rapidly be prevented by the adsorption of microsomal proteins on the surface of the fibres. It is not inhibited by superoxide dismutase, catalase and mannitol, indicating that oxygen radicals are not involved in the reaction. It is also not inhibited by desferrioxamine, indicating that it is not due to a release of free iron ions in solution from the fibres. Lipid peroxidation in NADPH-supplemented microsomes is also greatly increased upon addition of magnetite. This could be linked to the presence of ferrous ions in this solid iron oxide, since the ferric oxides haematite and goethite are completely inactive.

Unfolding of iron and copper complexes of human lactoferrin and transferrin

1. 1. Human lactoferrin and transferrin are capable of binding two iron or copper ions into specific binding sites in the presence of bicarbonate. 2. 2. Urea and several alkyl ureas have been effective in unfolding these metal-protein complexes. 3. 3. Biphasic transitions are observed for the unfolding of each of the metal complexes of these proteins as determined by direct visible spectroscopy suggesting the release of iron(III) and Cu(II) ions from both of these metal-binding proteins during the unfolding process. 4. 4. Greater stabilization and increased resistance to protein unfolding is observed for all iron(III) complexes compared to Cu(II) complexes of lactoferrin and transferrin as determined by isothermal unfolding and thermal denaturation. 5. 5. Relative stabilization of the different metal-protein complexes investigated within this study were determined to be as follows: Lf-Fe(III)⪢Lf-Cu(II); Tf-Fe(III)⪢Tf-Cu(II), and Lf-Fe(III)⪢Tf-Fe(III); Lf-Cu(II)⪢Tf-Cu(II).

Effects of alloyed molybdenum on the kinetics of repassivation on austenitic stainless steels

The kinetics of repassivation of Type 316L austenitic stainless steel in aqueous solutions after in situ generation of the metal surface have been obtained. The results are compared with those obtained previously from similar experiments on Type 304L stainless steel. In alkaline and slightly acidic solutions both alloys repassivate at a rate controlled by ion migration through the growing oxide film under high electric field. The presence of alloyed molybdenum accelerates the rate in the early stages of film growth but in the later stages the kinetics for the two materials are identical. In strongly acidic solutions dissolution of the iron component of the oxide film accompanies film growth. This constructive dissolution process occurs at a rate controlled by the diffusion of iron ions through the oxide matrix. While the presence of molybdenum does not affect the diffusion coefficient significantly, it does allow the release of iron ions to the solution to commence at a far earlier stage of film growth, thereby hastening the onset of passivity. The associated kinetic parameters are presented and the implications of the proposed mechanisms discussed.