Relative survival in elderly European cancer patients: evidence for health care inequalities. The EUROCARE Working Group

This paper examines the survival of elderly European cancer patients, on the basis of the EUROCARE II results. Using Hakulinen and Abeywickrama's method, the relative survival rates at 1 and 5 years from diagnosis were computed by sex and quinquennial age group for the elderly (65-99 years old). Age-standardised rates for the whole elderly group were also calculated. The analysis covered: all malignancies combined, stomach, colon, rectum, pancreas, lung, melanoma, bladder, kidney and non-Hodgkin's lymphomas for both sexes; prostate and larynx for men; and breast, ovary, uterine cervix and corpus for women. Data relating to 701521 cancer patients came from 44 population-based cancer registries in 16 European countries. The relative risks of death (RRs) of older patients (65-99) with respect to middle-aged adults (55-64) were computed by sex and country, for all malignancies only. The most prominent finding was the decrease in survival rates with increasing age for almost all cancer sites. The age-curves of survival rates at 1 year from diagnosis usually had a steeper slope than those at 5 years, particularly in women. This suggests that disease stage at presentation plays an important role in determining survival, particularly in the elderly. Thus, all factors which influence timing diagnosis in the elderly and cause a delay in tumour detection, such as psycho-social factors, access to care, co-morbidities and other clinical features affecting performance status, are very important predictors of prognosis. Very large geographic variations in relative survival rates were found among European countries. The ordering of countries was similar for almost all cancer sites. Western and Central Europe generally had the best survival, followed by Northern countries and by Southern ones (the latter with survival around the European average: 39% in men, 47% in women). The UK had survival rates unexpectedly lower than rates of nearest nations, often below the European average. Eastern countries usually had the lowest rates. In the very elderly patients (over 85 years), an apparent rise in the survival rates was noted, particularly at 5 years from diagnosis and in men. This 'too good' survival is unlikely to be due to real better prognosis, but rather to a selection bias. Countries with this unusual rise are also those registering a high proportion of DCO cases (those cases retrieved by death certificate only) (around 10%) or DCO unavailable. Another 'natural' bias has also to be taken into account: in elderly patients with a very bad prognosis, who are often suffering from other serious co-morbid conditions, cancer diagnoses could be under-notified and not reach at all the data sources commonly monitored by cancer registries.

Characterisation of a cDNA encoding gamma-glutamylcysteine synthetase in Medicago truncatula

A gamma-ECS cDNA from Medicago truncatula was isolated using an Arabidopsis thaliana cDNA as probe. The analysis of the amino acid sequence deduced from this cDNA revealed 80% identity with the gamma-ECS from A. thaliana and Brassica juncea and suggested a plastidial localisation for the enzyme. Gamma-ECS activity and high level of GSH were detected in the gamma-ECS-deficient E. coli strain expressing a fusion protein containing the M. truncatula gamma-ECS protein. Southern blot analysis suggests that gamma-ECS is encoded by a small multigenic family in M. truncatula and shows that homologous genes are present in two other leguminous plants, Medicago sativa and Pisum sativum. Gamma-ECS gene expression was analysed by Northern blot in seedlings, plantlets and mature plants.

Characterization of an atypical superoxide dismutase from Sinorhizobium meliloti

Sinorhizobium meliloti Rm5000 is an aerobic bacterium that can live free in the soil or in symbiosis with the roots of leguminous plants. A single detectable superoxide dismutase (SOD) was found in free-living growth conditions. The corresponding gene was isolated from a genomic library by using a sod fragment amplified by PCR from degenerate primers as a probe. The sodA gene was located in the chromosome. It is transcribed monocistronically and encodes a 200-amino-acid protein with a theoretical M(r) of 22,430 and pI of 5. 8. S. meliloti SOD complemented a deficient E. coli mutant, restoring aerobic growth of a sodA sodB recA strain, when the gene was expressed from the synthetic tac promoter but not from its own promoter. Amino acid sequence alignment showed great similarity with Fe-containing SODs (FeSODs), but the enzyme was not inactivated by H(2)O(2). The native enzyme was purified and found to be a dimeric protein, with a specific activity of 4,000 U/mg. Despite its Fe-type sequence, atomic absorption spectroscopy showed manganese to be the cofactor (0.75 mol of manganese and 0.24 mol of iron per mol of monomer). The apoenzyme was prepared from crude extracts of S. meliloti. Activity was restored by dialysis against either MnCl(2) or Fe(NH(4))(2)(SO(4))(2), demonstrating the cambialistic nature of the S. meliloti SOD. The recovered activity with manganese was sevenfold higher than with iron. Both reconstituted enzymes were resistant to H(2)O(2). Sequence comparison with 70 FeSODs and MnSODs indicates that S. meliloti SOD contains several atypical residues at specific sites that might account for the activation by manganese and resistance to H(2)O(2) of this unusual Fe-type SOD.

Differential regulation of two divergent Sinorhizobium meliloti genes for HPII-like catalases during free-living growth and protective role of both catalases during symbiosis

Two catalases, KatA and KatB, have been detected in Sinorhizobium meliloti growing on rich medium. Here we characterize a new catalase gene encoding a third catalase (KatC). KatC activity was detectable only at the end of the stationary phase in S. meliloti growing in minimum medium, whereas KatA activity was found during the exponential phase. Analysis with a katC-lacZ fusion demonstrated that katC expression is mainly regulated at the transcription level. An increase of catalase activity correlating with KatA induction was detected in bacteroids. A dramatic decrease of nitrogen fixation capacity in a katA katC double mutant was observed, suggesting that these catalases are very important for the protection of the nitrogen fixation process.

Direct detection of radicals in intact soybean nodules: presence of nitric oxide-leghemoglobin complexes

Electron paramagnetic resonance spectroscopy has been employed to examine the nature of the metal ions and radicals present in intact root nodules of soybean plants grown in the absence of nitrate. The spectra obtained from nodules of different ages using this non-invasive technique show dramatic differences, suggesting that there are both qualitative and quantitative changes in the metal ion and radical species present. A major component of the spectra obtained from young nodules is assigned to a complex (Lb-NO) of nitric oxide (NO.) with the heme protein leghemoglobin (Lb). This Lb-NO species, which has not been previously detected in intact root nodules of plants grown in the absence of nitrate, is thought to be formed by reaction of nitric oxide with iron(II) leghemoglobin. The nitric oxide may be generated from arginine via a nitric oxide synthase-like activity present in the nodules of the soybean plants, in a manner analogous to that recently described for Lupinus albus. This Lb-NO complex is present at lower concentrations in older nodules, and is almost completely absent from senescent nodules. Exposure of young and mature nodules to oxidant stress, in the form of hydrogen peroxide, results in changes in the EPR spectra, with the loss of the signals from the Lb-NO complex and appearance of absorptions similar to those from untreated senescent nodules. These results suggest that there are characteristic changes in both the metal ion complexes and radicals present in intact root nodules of different ages, and support the theory that nitric oxide and other radicals play a significant role in determining the nitrogen fixing activity of root nodules; the modulatory activity of NO. may involve regulation of gene activity.

Absence of synproportionation between oxy and ferryl leghemoglobin. off

The synproportionation reaction between ferryl leghemoglobin and oxyleghemoglobin does not occur, at least under conditions where this process could be clearly demonstrated with myoglobin and hemoglobin. In contrast, a cross synproportionation can occur between oxyleghemoglobin and ferryl myoglobin or between ferryl leghemoglobin and oxymyoglobin. The non-exposure, at the surface of the leghemoglobin molecule, of the nearest tyrosine residue to the heme group could explain this behaviour. Thus leghemoglobin per se does not appear to be able to act as an antioxidant in removing H2O2 by synproportionation. However, in the presence of ascorbate and/or glutathione which can reduce ferryl leghemoglobin, this hemoprotein could act as an H2O2-removing antioxidant, in a process similar to that described for myoglobin. This could also explain why, despite the absence of synproportionation, ferryl leghemoglobin is not detected in nodule extracts.

Leghemoglobin-derived radicals. Evidence for multiple protein-derived radicals and the initiation of peribacteroid membrane damage

Reaction of H2O2 with ferric leghemoglobin (metLb, the monomeric, oxygen-carrying, heme protein from root nodules of nitrogen-fixing plants) has been previously shown to generate an iron(IV)-oxo (ferryl) species and at least one protein radical. The latter has been suggested to be a tyrosine-derived phenoxyl radical present at Tyr-133 in the soybean protein and Tyr-138 in the lupin protein. To obtain further information on these protein radicals and their potential interaction with the physiologically important peribacteroid membrane (which surrounds the microsymbiont in vivo), EPR spin trapping studies have been carried out with soybean metLb. Evidence has been obtained for at least two additional protein-derived radicals in addition to the phenoxyl radical; these radicals are transient and reactive in nature. These species are carbon-centered, and at least one is a tertiary species (.CR1R2R3); these radicals may be side chain- or alpha-carbon-derived, their exact sites have not been determined. Some of these radicals are on the protein surface and may be key intermediates in the formation of protein dimers. These radicals have been shown to be capable of reacting with peribacteroid membrane fractions, with the consequent generation of lipid-derived radicals. The formation of such radicals may result in the depletion of membrane antioxidants and the initiation of lipid peroxidation. This transfer of damage from the heme center via the protein surface to neighboring membranes may be of considerable biological significance; the destruction of this membrane is one of the earliest observable events in root nodule senescence and is associated with the loss of nitrogen-fixing activity.

Cloning and characterization of the katA gene of Rhizobium meliloti encoding a hydrogen peroxide-inducible catalase

To investigate the involvement of bacterial catalases of the symbiotic gram-negative bacterium Rhizobium meliloti in the development of Medicago-Rhizobium functional nodules, we cloned a putative kat gene by screening a cosmid library with a catalase-specific DNA probe amplified by PCR from the R. meliloti genome. Nucleotide sequence analysis of a 1.8-kb DNA fragment revealed an open reading frame, called katA, encoding a peptide of 562 amino acid residues with a calculated molecular mass of 62.9 kDa. The predicted amino acid sequence showed a high homology with the primary structure of monofunctional catalases from eucaryotes and procaryotes. The katA gene was localized on the chromosome, and the katA gene product was essentially found in the periplasmic space. A katA::Tn5 mutant was obtained and showed a drastic sensitivity to hydrogen peroxide, indicating an essential protective role of KatA. However, neither Nod nor Fix phenotypes were impaired in the mutant, suggesting that KatA is not essential for nodulation and establishment of nitrogen fixation. Exposure to a sublethal concentration of H2O2 enhanced KatA activity (100-fold) and also increased survival to subsequent H2O2 exposure at higher concentrations. No protection is observed in katA::Tn5, indicating that KatA is the major component of an adaptive response.

Immunity status to polioviruses among non-European union immigrants in Veneto Region (North-East Italy)

Widespread use of poliovirus vaccines has lead to a dramatic decline on the incidence of paralytic poliomyelitis in the Western Hemisphere. In Italy, the use of live attenuated vaccine (OPV) has lead to virtual eradication of poliomyelitis. However, wild poliovirus is still endemic in some less developed countries, and there is still a risk of importation of wild-virus poliomyelitis as result of immigration from these areas. Therefore, a serologic study of the immunologic status to poliovirus was carried out in 242 immigrants from less developed countries in the Veneto Region (North-East Italy). The overall prevalence of serum neutralizing antibodies was 98.3 percent for poliovirus type 1, 99.6 percent for type 2, and 95.9 percent for type 3. The modal titres were 1:128 (21.1 percent), 1:512 (26.4 percent), and 1:32 (22.3 percent) for poliovirus type 1, type 2, and type 3, respectively. No subject was simultaneously lacking neutralizing antibodies to all three polioviruses. The mean duration of stay in Italy before testing was 1.53 years (range 1 month to 7 years). These results show a good level of the immunity status, similar to those found in the Veneto general population. Although the risk of paralytic poliomyelitis in our population is very low, seronegative immigrants originating from areas of high endemicity could reintroduce wild poliovirus. It is therefore important to maintain a careful surveillance system on the importation of wild poliovirus and to plan vaccination programs for unprotected immigrants.

Reaction of ferric leghemoglobin with H2O2: formation of heme-protein cross-links and dimeric species

Ferric leghemoglobin in the presence of H2O2 is known to give rise to protein radicals, at least one of which is centred on a tyrosine residue. These radicals are quenched by at least two processes. The first one involves an intramolecular heme-protein cross-link probably involving the tyrosine radical; this leads to the formation of a green compound with spectral characteristics differing markedly from those of ferryl and ferric leghemoglobin. This green compound cannot be reduced by dithionite or ascorbate, precluding any role for this species as an oxygen carrier. It exhibits modified EPR and pyridine haemochromogen spectra, indicating that alterations occur at the porphyrin macrocycle level. The additional compound previously described [Puppo, A., Monny, C. and Davies, M.J. (1993) Biochem. J. 289, 435-438] appears to be a mixture of ferry Lb and this green compound. The second quenching route results in the formation of intermolecular cross-links and hence dimeric forms of the protein. Ascorbate and glutathione inhibit both this intermolecular dimer formation and the formation of the intramolecular haem-protein cross-links and are likely to play a protective role in vivo.

The reactivity of ascorbate with different redox states of leghaemoglobin

Ascorbate has been previously shown to reduce the short-lived and reactive ferryl [Fe(IV) = O] states of myoglobin and haemoglobin. In this study it is shown that ascorbate is also able to reduce the otherwise long-lived and stable ferryl species [Lb(IV)] formed by the reaction of ferric or ferrous soybean leghaemoglobin with H2O2. The conversion of the ferryl species to ferric Lb, which appears to be moderately fast, is followed by a slow conversion of ferric Lb to oxyLb, by way of dexoy ferrous Lb. No reaction between ascorbate and oxyLb has been observed, in contrast to the previously reported pro-oxidant effect of ascorbate on oxymyoglobin. The addition of ascorbate prior to H2O2 to ferric Lb also prevents the formation of an additional species (which is not observed with myoglobin or haemoglobin); the optical spectra and migration on isoelectric focusing gels of this compound differ markedly from that of Lb(IV). When added after H2O2, ascorbate is able to reduce slowly this additional compound to oxyLb. These reactions are likely to occur in vivo as high ascorbate concentrations have been detected in soybean nodules. The reduction of Lb(IV) to ferric Lb is accompanied by oxidation of ascorbate, which has been detected by loss of the parent molecule in optical experiments and by the direct detection of ascorbate radicals by electron paramagnetic resonance (EPR) spectroscopy.(ABSTRACT TRUNCATED AT 250 WORDS)

Uptake of iron by symbiosomes and bacteroids from soybean nodules

Symbiosomes and bacteroids isolated from soybean nodules are able to take up the iron-citrate complex. The kinetics are characterized by initial high rates of iron internalization, and ATPase inhibitors significantly lower the uptake. This is consistent with an energy-dependent process on both membranes, although the involvement of a simultaneous facilitated diffusion can not be completely ruled out. Citrate alone is poorly absorbed by symbiosomes; this uptake is greatly enhanced by addition of iron. Iron-citrate was found both in the nodule cytosol and in the bacteroids. These results provide the first experimental evidence for the existence, at least in young nodules, of an important iron trafficking system from the plant host cell to the microsymbiont, through the peribacteroid membrane.

The reactivity of thiol compounds with different redox states of leghaemoglobin: evidence for competing reduction and addition pathways

Reaction of the ferric form of leghaemoglobin with hydrogen peroxide has been previously shown to give rise to an iron(IV)-oxo (ferryl) species, and a protein radical. Inclusion of a variety of thiol compounds in this system is shown to lead to rapid loss of the iron(IV)-oxo species and the regeneration of the ferric form and/or the formation of novel sulf species formed by nucleophilic attack of the thiol group on the tetrapyrrole ring. The reduction process also results in the generation of thiyl radicals which have been detected by EPR spin trapping. The relative yields of the products produced by these two competing pathways is shown to be highly dependent on the steric and electronic characteristics of the thiol compound. Evidence has also been obtained, in the absence of hydrogen peroxide, for both the reduction of the ferric form of the protein to the oxy-ferrous form, via a process believed to involve the deoxy-ferrous species, and the formation of sulf-leghaemoglobin species. Both of these pathways are again highly dependent on the structure of the thiol, and the former also results in the generation of thiyl radicals. Inclusion of the sulfide anion in place of the organic thiols results in somewhat different behaviour, in that this species appears to both reduce the iron centre and form a complex with the iron atom. This ligation process is reversible, and the sulfide complex is shown to react readily with both strong oxidizing and reducing agents. The behaviour of this protein, which is structurally related to myoglobin, is dramatically different to that demonstrated by myoglobin; this is rationalized in terms of the much more open heme site of leghaemoglobins, and the presence of an electronic gate which hinders access by negatively charged molecules. The contribution of these processes to the maintenance of the leghaemoglobin proteins in the oxy-ferrous form in vivo and the binding of oxygen is discussed.

Identification of the site of the globin-derived radical in leghaemoglobins

Reaction of the Fe3+ form of the oxygen-carrying protein leghaemoglobin (MetLb), derived from the root nodules of lupins, with H2O2 is shown to generate, in addition to an iron (IV)-oxo (ferryl) species, a globin radical. This radical has been detected by EPR spectroscopy and is analogous to the species previously observed with the soybean protein. Analysis of the hyperfine coupling constants and g value of the EPR signal, together with computer simulations and the similarity of the observed spectra of that detected with the soybean form suggest that this species is also a tyrosine-derived phenoxyl radical; this species is believed to arise via an electron-transfer process within the protein with an electron being transferred from the tyrosine residue to an initially-generated Compound-1-type species. Comparison of the protein sequences and structures of the two proteins show that there is only one conserved tyrosine residue (at position 133 in the soybean and 138 in the lupin); this is believed to be the site of the phenoxyl radical. The lupin phenoxyl radical reacts with added water-soluble antioxidants and reducing agents which result in repair of the radical; this may be an important protective mechanism in vivo. Analysis of molecular models of the protein structures is in accord with both the assignment of the radical to this conserved tyrosine residue and the observed radical reactivity.

How is leghemoglobin involved in peribacteroid membrane degradation during nodule senescence?

An increase in the rate of succinate and glutamate uptake by isolated symbiosomes from French bean nodules was observed in the presence of iron plus H2O2. The lipid bilayer, and not proteins involved in transport, seems to be the major target of radical attack. Leghemoglobin in the presence of a 6-fold excess of H2O2 (where heme breakdown and iron release occurred) provoked also an increase in peribacteroid membrane permeability. In contrast, this hemoprotein in the presence of a 2-fold excess of H2O2 (where a protein radical was generated) was without effect. We suggest that in vivo the release of heme iron may constitute the major process concerning the involvement of leghemoglobin in the degradation of the peribacteroid membrane during nodule senescence.

Glutathione-dependent conversion of ferryl leghaemoglobin into the ferric form: a potential protective process in soybean (Glycine max) root nodules

GSH is able to reduce soybean (Glycine max) ferryl-leghaemoglobin [Lb(IV)] formed by the reaction of ferric or ferrous Lb with H2O2; in both cases, ferric Lb is obtained and GSH is incapable of reducing ferric Lb to ferrous Lb. Furthermore, the addition of GSH before H2O2 to ferric Lb prevents side reactions which lead to a species whose spectrum differs markedly from that of Lb(IV). These reactions are likely to occur in vivo, as high GSH concentrations have been detected in soybean nodules. The GSH-dependent reduction of Lb(IV) is associated with the oxidation of GSH to GSSG. E.s.r. experiments show that the glutathione thiyl radical (GS.) is formed during this reaction. In the case of ferric Lb, both ferryl Lb and a globin-derived radical previously described appear to be involved in the formation of GS.. Both of these processes may be protective and can help account for the exclusive presence of ferrous (oxygenated or not) Lb in functioning nodules.

[Acute myocardial infarct and coronary artery aneurysm during pregnancy]

We present the first published case in Spain on a gestant woman with acute myocardial infarction. She was angiographically studied showing a coronary artery aneurysm with inner thrombus. This is also the first time that such a lesion is described in vivo in a gestant woman.

delta-Aminolevulinate uptake by Rhizobium bacteroids and its limitation by the peribacteroid membrane in Legume nodules

Heme is overproduced during Rhizobium-Legume symbiosis and delta-aminolevulinate (ALA) is a common precursor in both bacterial and plant synthesis pathways of this molecule. ALA uptake by bacteroids from French bean and soybean nodules was characterized. The action of several metabolic inhibitors and the competition effect of malate on this uptake were studied. ALA transport appeared to be mediated by the dicarboxylate carrier system. Purified symbiosomes--bacteroids surrounded by the peribacteroid membrane--failed to accumulate significant amount of ALA. These experiments rule out the possibility for the plant cytosol to provide the bacteroid with ALA and strengthen the restrictive role of the peribacteroid membrane for exchanges between the two symbiotic partners.

Direct detection of a globin-derived radical in leghaemoglobin treated with peroxides

The root nodules of leguminous plants contain an oxygen-carrying protein which is somewhat similar to myoglobin. Reaction of the Fe3+ form of this protein (metleghaemoglobin; MetLb) with H2O2 is known to generate a ferryl [iron(IV)-oxo] species. This intermediate, which is analogous to Compound II of peroxidases and ferryl myoglobin, is one oxidizing equivalent above the initial level. In the present study it is shown that the second oxidizing equivalent from the peroxide is rapidly transferred into the surrounding protein, generating a protein radical which has been detected by e.p.r. spectroscopy; this reaction is analogous to that observed with metmyoglobin. An identical protein-derived species is observed with all three forms of MetLb tested (a, c1, c3) and with a number of other hydroperoxides and two-electron oxidants. This latter result, the observation that the concentration of this species is not affected by certain hydroxyl-radical scavengers, and the loss of the radical when the oxy or deoxy forms are used, demonstrate that this species is formed by electron transfer within the protein rather than by the generation and subsequent reaction of hydroxyl radicals (and related species from the other hydroperoxides). The e.p.r. signal of this species, which decays rapidly with a half-life of approx. 40 s, is consistent with the formation of a sterically constrained tyrosine-derived phenoxyl radical; protein-iodination experiments lend support to this assignment. Reaction between the radical and a number of other compounds has been observed, demonstrating that it is at least partially exposed on the surface of the protein. Analysis of the protein structure suggest that the radical may be centred on a tyrosine residue present at position 132 in the protein; this residue is close to the haem prosthetic group, which would facilitate rapid electron transfer.

Lipid peroxidation in peribacteroid membranes from French-bean nodules

Enriched peribacteroid membranes were prepared from Phaseolus vulgaris nodules and, in the presence of metleghemoglobin and H(2)O(2), membranal lipid peroxidation was observed. The initial rate of the reaction was low and increased with time. Ferrous leghemoglobin was unable to induce this peroxidation with H(2)O(2). Thus, it appears that leghemoglobin (IV) is not the activated species involved in this process. Heme plays a role in this peroxidation and the hydroxyl radical is not an intermediate of the reaction. Lipid peroxidation in peribacteroid membranes was also observed in the presence of iron ions. A mixture of iron (III) and iron (II) produced a maximal peroxidation. Senescing nodule extracts were able to provoke membranal lipid peroxidation; they contained nonprotein-bound iron. Peribacteroid membranes were more sensitive than microsomes to peroxidation, as measured by malonaldehyde formation.

Scavenging of hypochlorous acid and of myoglobin-derived oxidants by the cardioprotective agent mercaptopropionylglycine

Mercaptopropionylglycine (MPG) has a marked cardioprotective action in several model systems of ischaemia-reoxygenation injury. Suggested mechanisms of action include scavenging of hydroxyl radical and of hypochlorous acid and reacting with an oxidant formed by reaction of myoglobin with H2O2, thereby slowing lipid peroxidation stimulated by myoglobin-H2O2 mixtures. This oxidant seems not to be singlet O2 or hydroxyl radical. Studies in vitro show that scavenging of hypochlorous acid is a feasible mechanism of cardioprotective action for MPG in vivo in ischaemia/reperfusion systems to which neutrophil-mediated injury contributes. However, the poor ability of MPG to inhibit lipid peroxidation stimulated by myoglobin/H2O2 mixtures and its ability to increase iron ion release from myoglobin in the presence of a large excess of H2O2 suggests that MPG is unlikely to protect the myocardium by interfering with oxidants produced by the myoglobin-H2O2 system.

Oxidation of dimethylsulphoxide to formaldehyde by oxyhaemoglobin and oxyleghaemoglobin in the presence of hydrogen peroxide is not mediated by "free" hydroxyl radicals

In the presence of excess hydrogen peroxide, human oxyhaemoglobin and oxyleghaemoglobin from soybean root nodules cause oxidation of dimethylsulphoxide to formaldehyde. This reaction is inhibited by thiourea but not by phenylalanine, HEPES, mannitol or arginine. It is concluded that dimethylsulphoxide oxidation is not mediated by "free" hydroxyl radicals, consistent with previous conclusions that intact haemoglobin, leghaemoglobin or myoglobin molecules do not react with H2O2 to form hydroxyl radicals detectable outside the protein.

Aromatic hydroxylation of phenylalanine as an assay for hydroxyl radicals: application to activated human neutrophils and to the heme protein leghemoglobin

Attack of hydroxyl radical (.OH), generated by a Fenton system at physiological pH, upon L-phenylalanine produces three isomeric tyrosines, o-tyrosine (2-hydroxyphenylalanine), m-tyrosine (3-hydroxyphenylalanine), and p-tyrosine (4-hydroxyphenylalanine). These may be separated by high-performance liquid chromatography and measured using an electrochemical detector. Since L-phenylalanine is relatively nontoxic, it is proposed that generation of these three tyrosines from phenylalanine can be used as an assay for .OH in biological systems. The use of the assay to measure .OH production by leghemoglobin (plus H2O2) and by activated human neutrophils is described. No .OH production by activated human neutrophils was observed unless a source of iron ions was added to the reaction mixture, which suggests that these cells do not release an iron "promoter" of .OH generation from superoxide and hydrogen peroxide.

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 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.