Free radicals and inflammation. Protection of phagocytosine leukocytes by superoxide dismutase

Isolated human polymorphonuclear leukocytes engaged in phagocytosis liberate superoxide radical and hydrogen peroxide into the surrounding medium. These two chemical species react to produce the hydroxyl radical, which attacks the leukocyte and leads to premature death of the cell. The hydroxyl radical may be scavenged by mannitol, or its formation can be prevented by the addition of superoxide dismutase or catalase to the medium, thereby eliminating the premature death of the cells. This phenomenon may partially explain the observed anti-inflammatory activity of superoxide dismutase.

Superoxide dismutases in polymorphonuclear leukocytes

Isolated human polymorphonuclear leukocytes were found to contain two distinct superoxide dismutases, electrophoretically identical to the superoxide dismutases found in other human tissues. One is inhibited by cyanide and is located in the cytosol. The other is not inhibited by cyanide and is mitochondrial. These findings disagree with reports by other laboratories, which did not find the cyanide-sensitive cytoplasmic enzyme. The superoxide dismutase-containing preparation of leukocytes released large amounts of superoxide into the medium when the cells were phagocytizing, suggesting that, if the cell population is homogeneous, superoxide production probably takes place on the outer surface of the cell membrane, in addition to inside the phagocytic vacuole.

Distribution of iron-containing superoxide dismutase in vascular plants

Superoxide dismutases (EC 1.15.1.1) in vascular plants representing different evolutionary levels were characterized using polyacrylamide gel electrophoresis. The three forms of the enzyme were distinguished from each other based on the following criteria: a) the Cu-Zn enzyme is sensitive to cyanide wherease the Fe and Mn enzymes are not; and b) the Cu-Zn and Fe enzymes are inhibited by H(2)O(2) whereas the Mn enzyme is H(2)O(2)-resistant. Of the 43 plant families investigated, the Fe-containing superoxide dismutase was found in three families: Gingkoaceae, Nymphaceae, and Cruciferae.

Determinants of linear growth and predictors of severe stunting during infancy in rural Malawi

Stunting is common among children under 5 y of age in sub-Saharan Africa. Several risk factors have been associated with poor growth but few studies have prospectively addressed the development of linear growth faltering and stunting during the first year of life. The present study was designed to analyse typical growth among rural Malawian infants, focusing particularly on the impact of birth size, adherence to feeding guidelines and morbidity in the development of severe stunting during infancy. A community-based cohort of 613 singleton newborns was prospectively followed by monthly home visits. Data were collected on the children's socioeconomic background, maternal size and weight gain during pregnancy, birth events, morbidity, breastfeeding and complementary feeding, growth and mortality. Univariate and multivariate analyses were used to determine associations between predictor variables and poor linear growth. The proportions of stunted infants (Height-for-age Z-score < -2) at 3, 6 and 9 mo of age were 27%, 51%, and 63%, respectively. At I y of age, over two-thirds (71%) of the infants were at least moderately (HAZ < -2) and 31% severely stunted (HAZ < -3).

CONCLUSION

The strongest predictor of severe stunting at 12 mo of age was small birth size. Other variables independently associated with this outcome included inappropriate complementary feeding, high morbidity, maternal short stature, male gender, and home delivery. Faltering of linear growth started soon after birth and continued throughout infancy. Interventions increasing birth size could have a significant role in the prevention of early childhood stunting. The ideal strategy should also emphasize the importance of appropriate infant feeding and decreasing the number of illness episodes amongst the infants.

Oxygen toxicity in Streptococcus mutans: manganese, iron, and superoxide dismutase

When cultured anaerobically in a chemically defined medium that was treated with Chelex-100 to lower its trace metal content, Streptococcus mutans OMZ176 had no apparent requirement for manganese or iron. Manganese or iron was necessary for aerobic cultivation in deep static cultures. During continuous aerobic cultivation in a stirred chemostat, iron did not support the growth rate achieved with manganese. Since the dissolved oxygen level in the chemostat cultures was higher than the final level in the static cultures, manganese may be required for growth at elevated oxygen levels. In medium supplemented with manganese, cells grown anaerobically contained a low level of superoxide dismutase (SOD) activity; aerobic cultivation increased SOD activity at least threefold. In iron-supplemented medium, cells grown anaerobically also had low SOD activity; aerobic incubation resulted in little increase in SOD activity. Polyacrylamide gel electrophoresis of the cell extracts revealed a major band and a minor band of SOD activity in the cells grown with manganese; however, cells grown with iron contained a single band of SOD activity with an Rf value similar to that of the major band found in cells grown with manganese. None of the SOD activity bands were abolished by the inclusion of 2 mM hydrogen peroxide in the SOD activity strain. S. mutans may not produce a separate iron-containing SOD but may insert either iron or manganese into an apo-SOD protein. Alternatively, iron may function in another activity (not SOD) that augments the defense against oxygen toxicity at low SOD levels.

Purification and characterization of an iron-containing superoxide dismutase from a eucaryote, Ginkgo biloba

A cyanide-insensitive superoxide dismutase was purified to electrophoretic homogeneity from leaves of the eucaryote, Ginkgo biloba L. A molecular mass of 47,000 was determined for the enzyme, which consisted of two subunits of equal size. The enzyme preparation contained two isoenzymes with isoelectric points of 5.25 and 5.15. Metal analysis after dialysis against EDTA revealed the presence of 1.4 gram atoms of iron per molecule. Approximately 2 gram atoms each of copper and zinc per enzyme molecule were also detected, although removal of copper by other chelators had no effect on enzymatic activity. The purified Ginkgo enzyme exhibited a sensitivity to hydrogen peroxide and insensitivity to cyanide, which is typical of iron-containing superoxide dismutases. Ginkgo iron superoxide dismutase was localized in the stroma of chloroplasts, but was absent from mitochondria. The enzyme from Ginkgo was most similar to iron superoxide dismutases of Nuphar, Brassica, and Escherichia coli when compared on the basis of S delta Q analysis of amino acid composition. Peptide fragments formed by proteolytic digestion of these four enzymes were compared qualitatively; similar-sized fragments which denote possible areas of homology were observed.

The importance of preterm births for peri- and neonatal mortality in rural Malawi

Peri- and neonatal mortality remain high in developing countries, especially in sub-Saharan Africa. In the present study, we quantified and identified the most important predictors of early mortality in rural Malawi. Data were obtained from a community-based cohort of 795 pregnant women and their 813 fetuses, followed prospectively from mid-pregnancy. In this group, peri- and neonatal mortality rates were 65.3 deaths per 1000 births and 37.0 deaths per 1000 live births respectively. When controlled for month of birth, maternal age and selected socio-economic variables, preterm birth was the strongest independent predictor of both peri- and neonatal mortality (adjusted odds ratios 9.6 for perinatal and 11.0 for neonatal mortality; 95% confidence intervals: [4.4, 21.0] and [3.7, 32.7] respectively). Weaker risk factors for mortality included a maternal history of stillbirth and abnormal delivery. Preterm delivery was associated with primiparity and peripheral malaria parasitaemia of the mother, and it accounted for 65% of the population-attributable risk for perinatal and 68% of the neonatal mortality. Successful intervention programmes to reduce peri- and neonatal mortality in Malawi have to include strategies to predict and prevent prematurity.

Purification of a catalase-peroxidase from Halobacterium halobium: characterization of some unique properties of the halophilic enzyme

A hydroperoxidase purified from the halophilic archaeon Halobacterium halobium exhibited both catalase and peroxidase activities, which were greatly diminished in a low-salt environment. Therefore, the purification was carried out in 2 M NaCl. Purified protein exhibited catalase activity over the narrow pH range of 6.0 to 7.5 and exhibited peroxidase activity between pH 6.5 and 8.0. Peroxidase activity was maximal at NaCl concentrations above 1 M, although catalase activity required 2 M NaCl for optimal function. Catalase activity was greatest at 50 degrees C; at 90 degrees C, the enzymatic activity was 20% greater than at 25 degrees C. Peroxidase activity decreased rapidly above its maximum at 40 degrees C. An activation energy of 2.5 kcal (ca. 10 kJ)/mol was calculated for catalase, and an activation energy of 4.0 kcal (ca. 17 kJ)/mol was calculated for peroxidase. Catalase activity was not inhibited by 3-amino-1,2,4-triazole but was inhibited by KCN and NaN3 (apparent Ki [KiApp] of 50 and 67.5 microM, respectively). Peroxidative activity was inhibited equally by KCN and NaN3 (KiApp for both, approximately 30 microM). The absorption spectrum showed a Soret peak at 404 nm, and there was no apparent reduction by dithionite. A heme content of 1.43 per tetramer was determined. The protein has a pI of 3.8 and an M(r) of 240,000 and consists of four subunits of 60,300 each.

Immunocytochemical evidence for a peroxisomal localization of manganese superoxide dismutase in leaf protoplasts from a higher plant

The controversial question of the intracellular location of manganese-containing superoxide dismutase in higher plants was examined under a new experimental approach by applying the more rigorous and specific methods of immunocytochemistry to protoplasts isolated fromPisum sativum L. leaves. Manganese superoxide dismutase (EC 1.15.1.1) was purified to homogeneity from 15 kg of leaves ofPisum sativum L. Rabbits were immunized with the mangano enzyme and the antibody specific for pea manganese superoxide dismutase was purified and found not to contain antigenic sites in common with (i) human manganese superoxide dismutase, (ii) iron superoxide dismutase from eitherEscherichia coli or higher plants, or (iii) plant or animal cuprozinc-superoxide dismutase.Pisum sativum L. manganese superoxide dismutase only appears to have antigenic determinants similar to other manganese superoxide dismutases from higher land plants. The antibody to pea Mn-superoxide dismutase was used to locate the enzyme in protoplasts isolated from young pea leaves by indirect immunofluorescence, and by electron microscopy using the unlabelled antibody peroxidase-antiperoxidase method. Results from immunofluorescence showed that chloroplasts were devoid of specific fluorescence which appeared scattered over the cytosolic spaces among chloroplasts, and demonstrate the absence of manganese superoxide dismutase inside chloroplasts. The metalloenzyme was found to be localized only in peroxisomes, whereas mitochondria, the traditionally accepted site for this enzyme in many eukaryotic organisms, did not show any specific staining. The possible subcellular roles of manganese superoxide dismutase inPisum sativum L. leaves are discussed in the light of its peroxisomal location.

Absence of the iron-containing superoxide dismutase in mitochondria from mustard (Brassica campestris)

Mitochondria were isolated from mature leaves as well as etiolated seedlings of Brassica campestris (mustard), a eukaryote previously shown to possess the iron-containing isoenzyme of superoxide dismutase. On the basis of KCN- and H2O2-sensitivity, and on polyacrylamide-gel analysis, only the cuprozinc and mangano superoxide dismutases were found in mitochondria. The iron-containing enzyme was absent. The mangano enzyme was found in the mitochondrial matrix, whereas the cuprozinc enzyme appeared to be localized in the intermembrane space.

Understanding protein lids: structural analysis of active hinge mutants in triosephosphate isomerase

The conformational switch from open to closed of the flexible loop 6 of triosephosphate isomerase (TIM) is essential for the catalytic properties of TIM. Using a directed evolution approach, active variants of chicken TIM with a mutated C-terminal hinge tripeptide of loop 6 have been generated (Sun,J. and Sampson,N.S., Biochemistry, 1999, 38, 11474-11481). In chicken TIM, the wild-type C-terminal hinge tripeptide is KTA. Detailed enzymological characterization of six variants showed that some of these (LWA, NPN, YSL, KTK) have decreased catalytic efficiency, whereas others (KVA, NSS) are essentially identical with wild-type. The structural characterization of these six variants is reported. No significant structural differences compared with the wild-type are found for KVA, NSS and LWA, but substantial structural adaptations are seen for NPN, YSL and KTK. These structural differences can be understood from the buried position of the alanine side chain in the C-hinge position 3 in the open conformation of wild-type loop 6. Replacement of this alanine with a bulky side chain causes the closed conformation to be favored, which correlates with the decreased catalytic efficiency of these variants. The structural context of loop 6 and loop 7 and their sequence conservation in 133 wild-type sequences is also discussed.

Porcine superoxide dismutase. Isolation and characterization of a relatively basic cuprozinc enzyme

A cuprozinc superoxide dismutase has been isolated from pig liver. The enzyme is similar to previously described cuprozinc superoxide dismutases in that it is a dimer of about 32 000 molecular weight consisting of approximately two equally sized subunits, and 2 atoms of copper and two atoms of zinc per molecule. It differs, however, from previously described cuprozinc superoxide dismutases because of its higher isoelectric point; pI 6.8 vs 4.9 for bovine enzyme. The diffusion coefficient for the porcine enzyme was determined to be 7.53 x 10(-7) cm2 s-1, while the equivalent spherical hydrodynamic radius was computed as 28.5 A. The enzyme was observed to undergo self-association with time. Sulfhydryl interaction is postulated to be involved.

Epidemiology and predictors of infant morbidity in rural Malawi

In rural Malawi, 703 newborns were visited monthly for 1 year to describe the epidemiology and health-seeking behaviour during acute episodes of diarrhoea, respiratory infections (ARI) and malaria. On average, the infants suffered from 1.3 annual episodes (11.0 illness days) of diarrhoea, 1.1 episodes (9.4 days) of ARI and 0.7 episodes (4.8 days) of malaria. Multivariate analysis with polychotomous logistic regression indicated that the amount of morbidity was associated with the child's area of residence, weight in early life, number of siblings, father's marital status and the source of drinking water. Diarrhoea and malaria were most common at 6-12 months of age and during the rainy months whereas respiratory infections peaked at 1-3 months of age and in the cold season. Ten per cent of diarrhoea, 9% of ARI and 7% of malaria episodes lasted for more than 14 days. Fifty-eight infants died, giving case fatality rates of 1% for diarrhoea, 2% for ARI and 4% for malaria. One-third (37%) of the illness episodes were managed at home without external advice. A traditional healer was consulted in 16% of episodes and a medical professional in 55% of episodes. If consulted, traditional healers were seen earlier than medical professionals (median duration after the onset of symptoms 0.7 vs. 1.8 days, P < 0.001). Traditional healers were significantly more commonly used by those families whose infants died than by those whose infants did not die (odds ratio 1.8, 95% CI 1.1, 3.0). Our results emphasise the influence of seasonality, care and living conditions on the morbidity of infants in rural Malawi. Case fatality for diarrhoea, ARI and malaria was high and associated with health-seeking behaviour among the guardians. Future interventions must aim at early and appropriate management of common childhood illnesses during infancy.

Purification and characterization of a mesohalic catalase from the halophilic bacterium Halobacterium halobium

When subjected to the stress of growth in a relatively low-salt environment (1.25 M NaCl), the halophilic bacterium Halobacterium halobium induces a catalase. The protein has been purified to electrophoretic homogeneity and has an M(r) of 240,000 and a subunit size of approximately 62,000. The enzyme is active over a broad pH range of 6.5 to 10.0, with a peak in activity at pH 7.0. It has an isoelectric point of 4.0. This catalse, which is not readily reduced by dithionite, shows a Soret peak at 406 nm. Cyanide and azide inhibit the enzyme at micromolar concentrations, whereas maleimide is without effect. The addition of 20 mM 3-amino-1,2,4-triazole results in a 33% inhibition in enzymatic activity. The tetrameric protein binds NADP in a 1:1 ratio but does not peroxidize NADPH, NADH, or ascorbate. Although the enzymatic activity is maximal when assayed in a 50 mM potassium phosphate buffer with no NaCl, prolonged incubation in a buffer lacking NaCl results in inactive enzyme. Moreover, purification must be performed in the presence of 2 M NaCl. Equally as effective in retaining enzymatic function are NaCl, LiCl, KCl, CsCl, and NH4Cl, whereas divalent salts such as MgCl2 and CaCl2 result in the immediate loss of activity. The catalase is stained by pararosaniline, which is indicative of a glycosidic linkage. The Km for H2O2 is 60 mM, with inhibition observed at concentrations in excess of 90 mM. Thus, the mesohalic catalase purified from H. halobium seems to be similar to other catalases, except for the salt requirements, but differs markedly from the constitutive halobacterial hydroperoxidase.

Oxygen metabolism of catalase-negative and catalase-positive strains of Lactobacillus plantarum

Two catalase-negative strains of Lactobacillus plantarum and a strain producing the atypical, nonheme catalase were studied to determine if the ability to produce the atypical catalase conferred any growth advantage upon the producing strain. Both catalase-negative strains grew more rapidly than the catalase-positive strain under aerobic or anaerobic conditions in a glucose-containing, complex medium. Upon exhaustion of glucose from the medium, all three strains continued growth under aerobic but not under anaerobic conditions. The continued aerobic growth was accompanied by production of acetic acid in addition to the lactic acid produced during growth on glucose. Oxygen was taken up by exponential phase-cell suspensions grown on glucose when glucose or glycerol were used as substrates. Cells harvested from glucose-exhausted medium oxidized glucose, glycerol, and pyruvate. Oxygen utilization by a catalase-negative strain increased as did the specific activity of reduced nicotinamide adenine dinucleotide peroxidase during late growth in the glucose-exhausted medium. The catalase-positive strain and the catalase-negative strain tested both possessed low but readily detectable levels of superoxide dismutase throughout growth. The growth responses are discussed in terms of the presence of enzymes which would allow the cells to remove potentially damaging reduction products of O2.

Chemiluminescence in Wounded Root Tissue : EVIDENCE FOR PEROXIDASE INVOLVEMENT

Root and stem segments from soybean (Merrill cv. ;Bragg') showed an enhanced chemiluminescence upon mechanical injury. Roots emitted more light than did stems. Light emission was diminished by CN(-) and N(3) (-) but was not affected by rotenone and antimycin A. Catalase quenched chemiluminescence in wounded root segments as did ascorbic acid and hydroquinone. Superoxide dismutase addition resulted in a small diminution in light emission, but mannitol, an OH. scavenger, was without effect. The addition of H(2)O(2) to wounded root segments markedly elevated chemiluminescence in the presence of air as well as under N(2). It is concluded that peroxidases, found abundantly in roots, predominantly contribute to light emission in wounded plant tissue.

Chloroplast and mitochondrial mechanisms for protection against oxygen toxicity

As a consequence of their oxygen rich environment, organelles of photosynthetic tissues are exposed to large fluxes of oxyradicals and reactive oxygen species. Superoxide, hydrogen peroxide, hydroxyl radical and singlet oxygen are all potential by-products of respiratory and photosynthetic systems. Strong reductants found in mitochondria and chloroplasts along with a steady flux of photosynthetically generated oxygen enhance the potential for oxyradical production. Unless neutralized by scavenger substrates or enzymes, these reactive intermediates pose a lethal threat. The presence of superoxide dismutases, catalases, various peroxidases and scavenger substrates are all means of defences available to protect organelles. A balance between oxyradical production and neutralization should exist. Perturbations in generation or in sequestration caused by environmental or nutritional factors might profoundly alter the steady state level of oxyintermediates.

Cloning and determination of the nucleotide sequence of the Mn-containing superoxide dismutase gene from Halobacterium halobium

A group of synthetic 17-mer oligodeoxynucleotides (oligos) was constructed to correspond to a sequence of amino acids situated near the N terminus of the manganese-containing superoxide dismutase (Mn-SOD) purified from the halophilic bacterium, Halobacterium halobium. A cosmid library of a Sau3AI partial digest of halobium DNA, cloned into the BamHI site of pHC79, was probed with the radiolabeled oligos. Cosmid DNA was purified from the clone that showed hybridization at the highest stringency. A 1.8-kb PstI fragment of this DNA which hybridized the probes was subcloned into bacteriophage M13 and transfected into Escherichia coli JM101. The entire insert containing a 600-bp sequence coding for Mn-SOD and its 5'- and 3'-flanking regions was sequenced. The derived amino acid sequence of the structural gene showed a similarity to other manganese and iron-containing SODs in normally conserved regions.

Isolation and Characterization of an Iron-Containing Superoxide Dismutase From Water Lily, Nuphar luteum

A cyanide-insensitive superoxide dismutase (EC 1.15.1.1) was purified from leaves of the water lily Nuphar luteum (L.) Sibth. and Smith Subsp. macrophyllum (Small) Beal. The enzyme had a molecular weight of 46,000 and was composed of two equally sized subunits. Metal analysis showed the protein to contain about 1 gram atom of iron per dimer. The iron-containing superoxide dismutase was sensitive to H(2)O(2) as well as to azide. Antibody to the protein did not cross-react with iron superoxide dismutase isolated from the eucaryote Brassica or with algal extracts.

Purification of a manganese-containing superoxide dismutase from Halobacterium halobium

An oxygen-induced superoxide dismutase was purified from the halophilic bacterium, Halobacterium halobium, strain NRL. Due to the high salt requirement for enzyme stability, the purification had to be performed in the presence of 2 M NaCl. The pI of the protein was 4.95. The approximate Mr was 38,500. The subunit size as determined by sodium dodecyl sulfate-electrophoresis was approximately 19,000. Metal analysis showed 1.5 atoms of manganese per dimer, 0.5 atom zinc, and 1.54 atoms copper. The N-terminal sequence of amino acids was determined, and based upon the first 26 amino acids significant homology to other manganese- and iron-containing superoxide dismutases was revealed.

Antenatal and perinatal predictors of infant mortality in rural Malawi

BACKGROUND

The slow pace in the reduction of infant mortality in sub-Saharan Africa has partially been attributed to the epidemic of human immunodeficiency virus (HIV) infection. To facilitate early interventions, antenatal and perinatal predictors of 1st year mortality were identified in a rural community in southern Malawi.

METHODS

A cohort of 733 live born infants was studied prospectively from approximately 24 gestation weeks onwards. Univariate analysis was used to determine relative risks for infant mortality after selected antenatal and perinatal exposures. Multivariate modelling was used to control for potential confounders.

FINDINGS

The infant mortality rate was 136 deaths/1000 live births. Among singleton newborns, the strongest antenatal and perinatal predictors of mortality were birth between May and July, maternal primiparity, birth before 38th gestation week, and maternal HIV infection. Theoretically, exposure to these variables accounted for 22%, 22%, 17%, and 15% of the population attributable risk for infant mortality, respectively.

INTERPRETATION

The HIV epidemic was an important but not the main determinant of infant mortality. Interventions targetting the offspring of primiparous women or infants born between May and July or prevention of prematurity would all have considerable impact on infant survival.

Elevation of superoxide dismutase in Halobacterium halobium by heat shock

Exposure of Halobacterium halobium to 50 degrees C for 2.5 h in an aerobic environment resulted in a greater than twofold increase in the activity of the manganese-containing superoxide dismutase. Nondenaturing polyacrylamide gels stained for enzymatic activity did not reveal any additional isozymes of superoxide dismutase induced by the heat shock. The maximal effect was observed at 50 degrees C, and the elevated levels of activity remained constant during 5 h of recovery at 40 degrees C. The induction of enzymatic activity was sensitive to protein synthesis inhibitors. The results are discussed relative to heat shock and stress-related proteins as well as alterations in metabolism brought about by elevated temperatures.