Ambient Oxygen Conditions Research Articles

Oxidation and Corrosion of Silicon Nitride at 1200°C and 1500°C

The effect of different sintering additives on the high temperature oxidation and corrosion behaviour of Si3N4 ceramics is investigated. A corrosion furnace was set up which allows testing of ceramic discs at test temperatures upto 1500°C. It was possible to conduct tests under ambient oxygen conditions, or with increased water vapour as well as testing with corrosive gases such as HCl or SO2. Si3N4 was prepared with MgO, Al2O3, Y2O3 and Al2O3+Y2O3 sintering additives. These discs were subjected to different oxidation and corrosion test conditions at temperatures of 1200°C and 1500°C for upto 128 h. The effects that the different corrosion enviroments have on the corrosion resistance of the Si3N4 materials are presented.

Influence of Aging, Oxygen, and Moisture on Ethanol Production from Cabbage Seeds

A seed quality test developed by Kataki and Taylor (1997) measures the anaerobic-to-aerobic (ANA) ratio of ethanol production and the relationship of the ANA ratio index-to-seed quality has been tested in several species. To expand the usefulness of the ANA ratio index and to optimize the test conditions, a series of studies was performed using cabbage (Brassica oleracea L. var. capitata L.) seeds as a model. It was hypothesized that ethanol production in cabbage seeds would be influenced by aging treatment, hydration level, seed integrity (grinding), and oxygen availability. Cabbage seeds were subjected to controlled aging treatments (40 °C at 70% relative humidity for 0, 7, 14, 21, and 28 d). Seed samples were incubated with a glucose (50 mm) potassium phosphate buffer (5 mm, pH 5.6) at 25 °C for 24 h (shorter than the time required for germination). The water concentration levels tested in the current study were 0.18, 0.22, 0.54, 0.80, 1.22, 1.86, 3.00, 5.67, and 10.0 g of H2O per gram of dry seeds. Ethanol production was measured in the supernatant of seed extracts using immobilized enzyme technology. The experiments were performed in ambient oxygen conditions and under nitrogen. Ethanol production was greater in aged than nonaged intact seeds at all water concentrations tested. Nonaged seeds under nitrogen had reduced ethanol production at ≤0.54 g of water per gram of seeds, indicating that low seed water concentration limited ethanol production. Nonaged seeds in ambient oxygen at ≥1.22 g of water per gram of seeds had elevated ethanol production, indicating that a hypoxic environment was created by excess seed water. Thus, a water concentration between these values is recommended for the ANA ratio index test for cabbage seeds. The opposite trend of lower ethanol production in aged than nonaged seeds was measured if seeds were ground before the hydration. Seed integrity experiments suggest that lower ethanol production observed in aged ground seeds may be attributed to hypoxia resulting from rapid hydration damage that results with loss of seed-coat integrity.

Growing cells at 40% ambient oxygen conditions them to subsequent oxidative stress

Sirs, Although the influence of lipofuscin on cells and lysosomes is debated, it is considered to be either insignificant or damaging (reviewed in Terman et al. 2007; Kurz et al. in press; Brunk and Terman 2002). Recently, however, a paper (Stroikin et al. 2007) was published in Biogerontology that attributed to lipofuscin a new and stabilizing effect on lysosomes of starved fibroblasts. In that study it was concluded that lipofuscin in moderate amounts renders cells more, not less, resistant to starvation. Unfortunately, the experimental design does not seem to justify such conclusions. The cellular amount of lipofuscin was varied by growing cells for prolonged periods of time (months) at either 8% or 40% ambient oxygen, being an established method to restrict or enhance, respectively, lipofuscin formation (reviewed in Brunk and Terman 2002). The cellular response to oxidative stress, induced by starvation (Gaspar et al. 2006; Morales et al. 2004; Eisler et al. 2004), was then compared on the two groups of cells. However, growing cells at 40% oxygen also means exposing them to a condition of moderate oxidative stress and thereby preconditioning them to, and protecting them from, a later, more marked oxidative stress. This fact is described in relevant literature (Spitz et al. 1987; Tang et al. 2005; Fonager et al. 2002). In contrast, this is not the case for cells that have been grown at 8% oxygen before an ensuing oxidative stress. Therefore, the two groups in the study (Stroikin et al. 2007) were not directly comparable when they were exposed to starvation. Consequently, the observation that lipofuscinladen cells appeared more resistant to oxidative stress than non-lipofuscin-laden ones may not be attributable to the lipofuscin per se but, rather, to the fact that one of the groups had been conditioned by exposure to an elevated concentration of oxygen. No control experiments were done to rule out this objection, and in the absence of such controls it is not possible to draw the conclusions made in the paper (Stroikin et al. 2007). Given that the consequences of lipofuscin accumulation are potentially important for our understanding of the mechanisms behind postmitotic ageing, solid experimental data on these matters are needed. Therefore, it would be most interesting if the authors repeated their experiments with correctly matched controls. For example, cells moved from 8% to 40% oxygen for a few days before starvation would be preconditioned to the ensuing stress without becoming significantly more lipofuscin-laden. U. T. Brunk (&) Division of Pharmacology, Faculty of Health Sciences, Linkoping University, Linkoping 581 85, Sweden e-mail: ulf.brunk@imv.liu.se

Ellagitannins have Greater Oxidative Activities than Condensed Tannins and Galloyl Glucoses at High pH: Potential Impact on Caterpillars

Plants synthesize a diversity of tannin structures but little is known about whether these different types have different oxidative activities in herbivores. Oxidative activities of hydrolyzable and condensed tannins were compared at pH 10 with two methods: EPR spectrometry was used to quantify semiquinone radicals in anoxic conditions and a spectrophotometric assay was used to measure the rate of browning of phenolics oxidized in ambient oxygen conditions. A little-studied group of hydrolyzable tannins (ellagitannins) contained the most active tannins examined, forming high concentrations of semiquinone radicals and browning at the highest rates. On average, galloyl glucoses and high-molecular-weight gallotannins had intermediate to low oxidative activities. Condensed tannins generally formed low levels of semiquinone radicals and browned most slowly. The results suggest that ellagitannin-rich plants have active oxidative defenses against herbivores, such as caterpillars, whereas the opposite may hold true for plants that contain predominantly condensed tannins or high-molecular-weight gallotannins.

Gene Expression Profile of Human Airway Epithelium Induced by Hyperoxia In Vivo

Hyperoxia leads to oxidative modification and damage of macromolecules in the respiratory tract with loss of biological functions. Given the lack of antioxidant gene induction with acute exposure to 100% oxygen, we hypothesized that clearance pathways for oxidatively modified proteins may be induced and serve in the immediate cellular response to preserve the epithelial layer. To test this, airway epithelial cells were obtained from individuals under ambient oxygen conditions and after breathing 100% oxygen for 12 h. Gene expression profiling identified induction of genes in the chaperone and proteasome-ubiquitin-conjugation pathways that together comprise an integrated cellular response to manage and degrade damaged proteins. Analyses also revealed gene expression changes associated with oxidoreductase function, cell cycle regulation, and ATP synthesis. Increased HSP70, protein ubiquitination, and intracellular ATP were validated in cells exposed to hyperoxia in vitro. Inhibition of proteasomal degradation revealed the importance of accelerated protein catabolism for energy production of cells exposed to hyperoxia. Thus, the human airway early response to hyperoxia relies predominantly upon induction of cytoprotective chaperones and the ubiquitin-proteasome-dependent protein degradation system to maintain airway homeostatic integrity.

Macromolecular isoforms of Daphnia magna haemoglobin

The haemoglobin (Hb) of Daphnia magna acclimated to different oxygen conditions was sampled, and in its natively assembled state it was separated by chromatofocusing. The Hb isoforms were analysed for their subunit composition under denaturating conditions by two-dimensional gel electrophoresis. The Hb system is suggested to consist of three predominant Hb aggregates, which are characterised by a specific subunit composition and synthesised in response to different ambient oxygen conditions. In normoxia, a dominant Hb aggregate (DmHbI) with a pI of 4.4-4.6 was composed of subunits B, C, E, F and G. In severe hypoxia, a different dominant Hb isoform (DmHbIII) with a pI of 5.7-5.9 was composed of subunits A, B, C, D, E and F. Further analyses in moderate hypoxia provided evidence for a third Hb isoform (DmHbII) composed of subunits B, C, D, E and F. Sequence alignment and homology modelling of the tertiary structure of the D. magna Hb domains 1 and 2 revealed functionally relevant substitutions of amino acid residues at positions B10, E7 and E11, which determine the functional properties of D. magna haemoglobin in terms of haem contact, oxygen binding and affinity. Both domains are predicted to possess the common haemoglobin fold, but helices C and D are not properly formed, and helix G is interrupted by a short coil.

Natural killer cell-mediated basal and interferon-enhanced cytotoxicity against liver cancer cells is significantly impaired under in vivo oxygen conditions.

Current immunostimulatory treatment protocols of cancer are often met with little success. Several lines of evidence indicate that the tumour microenvironment may impair the cytotoxic activity of natural killer (NK) cells. In this study, the NK cell-mediated killing of liver-derived cells was investigated at oxygen concentrations conform to those present in the human body at physiological and pathological conditions. The in vivo-relevant oxygen concentrations corresponding to 1, 2 and 6% were compared to those of the ambient air (21%) for their effect on the lysis of four liver-derived cell lines and the highly susceptible K562 cells. Exposure to each of the hypoxic conditions had a significantly inhibitory effect on NK cytotoxicity. Treatment with interferon-alpha (IFN-alpha) in hypoxia enhanced the cytotoxic potential of the NK cells less than it enhanced the cytotoxicity at ambient oxygen conditions. In summary, the oxygen tension profoundly affects both the cytoxic activity of NK cells and their activation by IFN-alpha.

Suppression of Meloidogyne javanica by Pseudomonas aeruginosa IE-6S + in tomato: the influence of NaCl, oxygen and iron levels

Understanding the environmental factors that influence the suppression of disease-suppressive strains of Pseudomonas fluorescens is an essential step toward improving the level and reliability of their biocontrol activity. A 0.8 M NaCl concentration was optimal for in vitro survival and growth of IE-6S + while, nematicidal activity by IE-6S + was maximal when the bacterium was exposed to 0.4 M NaCl. The bacterium was highly sensitive to high (1.6 M) NaCl concentration. Culture filtrate of the bacterium resulting from the medium supplemented with 0.2 or 0.4 M NaCl showed the presence of secondary metabolite, hydrogen cyanide (HCN). Soil amendment with IE-6S + alone or in conjunction with up to 0.8 M NaCl enhanced bacterial efficacy towards Meloidogyne javanica, the root-knot nematode. Soil amendment with NaCl up to 0.8 M also resulted in enhanced bacterial rhizosphere colonization and growth of tomato seedlings. Protein content of the shoot was reduced when soil was amended with 1.6 M NaCl. Inner root establishment of the bacterium was greatly affected in the soils treated with 1.6 M NaCl. Under in vitro conditions, IE-6S + showed enhanced growth when kept at ambient oxygen conditions while the growth of bacterium affected when incubated at low oxygen conditions. Culture filtrate of the bacterium resulting from low oxygen level caused greater mortality of M. javanica juveniles in vitro compared with the filtrates obtained from ambient oxygen conditions. Culture filtrate from low oxygen conditions also showed the presence of hydrogen cyanide while those from ambient oxygen condition did not. Under glasshouse conditions, regardless of bacterial application, nematode penetration rate was greater when the pots were watered from the top; nematode penetration was lowered in bacterized pots compared with non-bacterized controls. IE-6S + applied in the pots either watered from the top or bottom had no significant impact on growth of tomato but protein contents of the leaves increased after treatment with the bacterium. Rhizosphere and inner root colonization of the bacterium increased when the pots were watered from the top. Under in vitro conditions, with an increased iron concentration in the form of FeEDDHA, growth of IE-6S + and its nematicidal activity increased. Culture filtrate of IE-6S + obtained from liquid King's B medium supplemented with 0.5 or 1.0 mM FeEDDHA showed the presence of HCN. Under glasshouse conditions, soil treated with FeEDDHA alone did not reduce nematode penetration rates but did reduce greatly when applied in conjunction with IE-6S +. FeEDDHA applied at 0.5 mg/kg of soil in combination with IE-6S + significantly enhanced plant growth and leaf protein contents. FeEDDHA at 1 mg/kg of soil increased bacterial populations both in the rhizosphere and inner root tissues of tomato.

Effect of taurine and other antioxidants on the growth of colon carcinoma cells in the presence of doxorubicin or vinblastine in hypoxic or in ambient oxygen conditions: effect of antioxidants on the action of antineoplastic drugs in MDR and non-MDR cells.

Clinical cancer treatments are limited by the emergence of cumulative dose-dependent deleterious side effects of chemotherapeutic agents, some which are irreversible. Many of these side effects involve oxidative stress originating with the generation of reactive oxygen species (ROS) by chemotherapeutic agents, such as the anthracyclines1,2.KeywordsLoVo CellHydroxy Free RadicalTaurine ChloramineLoVo Cell LineDoxorubicin ToxicityThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Susceptibility of human placental syncytiotrophoblastic mitochondria to oxygen-mediated damage in relation to gestational age.

When maintaining first trimester placental villi in organ culture under conventional normoxic conditions, we have observed widespread degeneration of the syncytiotrophoblast within 24 h despite excellent viability for the cytotrophoblastic and stromal cell types. Here we identify loss of mitochondrial activity as an early event in this process. In the light of proposals that the early part of gestation occurs in a low oxygen environment and also reported associations between mitochondrial disruption and oxidative stress, we cultured first trimester villi under low oxygen conditions (2.5%). Mitochondrial superoxide dismutase (MnSOD) localization and activity at different gestational ages were also determined. It was found that syncytiotrophoblastic and mitochondrial morphology improved, and mitochondrial activity was retained for 6 h and more if 8- to 10-week-old tissue was placed into a low oxygen environment immediately after removal from the uterus. The effect of oxygen concentration was less marked when using tissue of 14 weeks or more gestational age, which showed good survival and retention of mitochondrial activity under both low and ambient oxygen conditions. This correlated with our finding that placental MnSOD activity increased significantly between 8 and 14 weeks of gestation. Immunohistochemistry demonstrated that at 11 weeks; MnSOD was localized predominantly within the cytotrophoblast cells, whereas by 16 weeks it was found in the syncytiotrophoblast also. These results indicate an acute sensitivity of first trimester placenta syncytiotrophoblast to oxygen-mediated damage.

Effect of oxygen concentration on in vitro fertilization and embryo culture in the human and the mouse

To compare the effect of culturing oocytes, zygotes and embryos under low (5%) versus ambient (20%) oxygen conditions on human IVF results and on mouse blastocyst formation. A prospective, randomized study of 257 consecutive IVF treatment cycles in 186 couples undergoing oocyte retrieval for various reasons of infertility. Gametes and resulting embryos after IVF were alternately allocated to fertilization and culture either under a gas phase of 5% CO2/90% N2/5% O2, or 5% CO2/95% air (20% O2). Oocytes and embryos from randomly bred and hybrid mouse strains were randomly allocated to culture under either of the two gas phases. A university hospital-based IVF-ET program. In the human, rates of fertilization, embryonic development at the time of embryo replacement (42 to 46 hours after insemination), pregnancy, and implantation were compared. In the mouse, the rates of blastocyst formation were compared. Clinical pregnancies occurred in 24.2% versus 19.4% of retrievals when culture took place under low oxygen versus ambient oxygen conditions. Fertilization, embryonic development, pregnancy, and implantation rates did not differ significantly between the groups. Slightly higher blastocyst rates occurred when mouse embryos from hybrid strains were cultured under low oxygen compared with culture under ambient oxygen conditions, whereas no such difference in blastocyst rates was found in randomly bred mouse embryos. This study failed to demonstrate any improvement in human IVF results associated with the use of a gas mixture of 5% CO2/90% N2/5% O2 during the first two days of development compared with the use of 5% CO2 in air.

Investigation of polymeric materials using the cone calorimeter

AbstractThe use of polymeric materials in building or construction applications is steadily increasing. Therefore, the potential for these materials to be exposed to fire is also increased. The understanding of the pyrolysis characteristics of these materials is thus a necessity. There are many standard tests used to evaluate materials. Unfortunately, the correlation between these tests and large scale fire is less than desirable. A new bench scale rate of heat release apparatus, the Cone Calorimeter, is now being used more frequently in pyrolysis testing of polymeric materials. This apparatus has been shown to correlate much better between room scale testing and large scale fire testing. The cone Calorimeter provides a pyrolysis profile of a material under ambient oxygen conditions. Characteristics such as ignition time, total heat release, maximum rate of heat release, mass loss during pyrolysis, CO2, CO, and smoke production are determined. In this work several almost neat polymers are examined and the general pyrolysis characteristics of these polymers are discussed. The objective of this work is to provide information of basic polymeric pyrolysis properties of these materials. Variations in the material, i.e., molecular weight, polydispersity, and residual catalysis, along with changes in testing procedures, can have dramatic effects on results. Obviously the addition of flame retardant and flame retardant packages to any of these materials will have dramatic effects on results.

Eimeria tenella: Growth and drug sensitivity in tissue culture under reduced oxygen

For Plasmodium falciparum in culture, growth is enhanced as oxygen tension is lowered and drug susceptibility, particularly susceptibility to 70S ribosomal and mitochondrial inhibitors, changes. Whether similar effects occur in Eimeria tenella was tested as a possible explanation for why certain 70S ribosomal inhibitors, while active in Eimerm-infected birds, are virtually inactive in vitro under ambient oxygen conditions. It was reasoned that perhaps these agents would exhibit good in vitro potency under reduced oxygen conditions. Such proved not to be the case, and it was further found that no positive effect on Eimeria growth occurred under these conditions. Finally, lowering oxygen tension had no substantial effects on sensitivity to anticoccidials or mitochondrial inhibitors.

CHANGE IN SYNTHESIS OF NON-ETHYLENE VOLATILES FOLLOWING APPLE FRUIT STORAGE IN ATMOSPHERES INDUCING ANAEROBIC METABOLISM.

Apple fruit storage lie is prolonged by low-oxygen cold storage, however, ethanol accumulates when oxygen concentration is reduced below the Pasteur point, Upon return to aerobic conditions, dissipation of ethanol occurs due to physical (evaporation) and biochemical processes. Oxidation of ethanol by apple fruit occurs at a slow rate, but ethanol also serves es a substrate for fruit volatile synthesis. This study was conducted to determine changes in concentrations of ethanol and other non-ethylene apple fruit volatiles following periods of anaerobiosis. `Delicious' apples were obtained from a commercial warehouse and stored at 0.05% O2, 0.2% CO2 and 1 C. One day following return to ambient oxygen conditions, several volatiles were identified from anaerobic fruit that were nor produced by the control fruit. All were eaters that contained an ethyl group as the alcohol-derived portion, These included ethyl acetate, ethyl butyrate, ethyl 2-methyl butyrate, ethyl hexanoate and ethyl octanoate. Several esters produced by the controls were not detectable from anaerobic fruit including butyl butyrate, butyl 2-methyl butyrate, propyl hexanoate and 3-methyl butyl hexanoate. After 7 days ripening at 20 C, the amount of ethanol and the additional ethylesters was reduced in anaerobic fruit. Synthesis of esters produced by control fruit but nor by anaerobic fruit during the initial volatile sampling had resumed after 7 days.

Regulation of Soybean Nitrogen Fixation in Response to Rhizosphere Oxygen

Nodule nitrogen fixation rates are regulated by a mechanism which is responsive to the rhizosphere oxygen concentration. In some legumes, this oxygen-sensitive mechanism appears to involve changes in the gas permeability of a diffusion barrier in the nodule cortex. In soybean evidence for such a mechanism has not been found. The purpose of this research was to make quantitative measurements of soybean nodule gas permeability to test the hypothesis that soybean nodule gas permeability is under physiological control and responsive to the rhizosphere oxygen concentration. Intact hydroponically grown soybean plants were exposed to altered rhizosphere oxygen concentrations, and the nodule gas permeability, acetylene reduction and nodule respiration rates were repeatedly assayed. After a change in the external oxygen concentration, nitrogenase activity and nodule respiration rates displayed a short-term transient response after which the values returned to rates similar to those observed under ambient oxygen conditions. In contrast to steady-state nitrogenase activity and nodule respiration, nodule gas permeability was dramatically affected by the change in oxygen concentration. Decreasing the external oxygen concentration to 0.1 cubic millimeter per cubic millimeter resulted in a mean increase in nodule gas permeability of 63%. Increasing the rhizosphere oxygen concentration resulted in decreased nodule gas permeability. These data are consistent with the hypothesis that soybean nodules are capable of regulating nitrogen fixation and nodule respiration rates in response to changes in the rhizosphere oxygen concentration and indicate that the regulatory mechanism involves physiological control of the nodule gas permeability.

Application of chlorite-sulfide-oxide equilibria to metamorphosed massive sulfide ores, Snow Lake area, Manitoba

The Stall Lake and Anderson Lake massive Cu-Zn sulfide deposits, situated in the Snow Lake area of northern Manitoba, occur in hydrothermally altered felsic volcanic rocks which have been subjected to amphibolite-grade metamorphism. Mineral assemblages from the two deposits contain in addition to chlorite, the f (sub O 2 ) -f (sub S 2 ) buffer assemblage of pyrite, pyrrhotite, and magnetite as well as quartz, aluminosilicate, and sphalerite.In P-T space, the mole fraction of daphnite in a chlorite solid solution may be represented by a series of isopleths of Fe/Sigma R (super +2) calculated at P (sub H 2 O) = P total for f (sub O 2 ) and f (sub S 2 ) buffered by pyrite, pyrrhotite, and magnetite. Calculations were based on an ideal ionic solution model for the daphnite component in chlorite (i.e., a daphnite = Fe (super +2) /Sigma R (super +2) = X daphnite ) and the free energy data for daphnite from Bryndzia and Scott (1987). Chlorite isopleths are very sensitive to changes in ambient oxygen and sulfur fugacity conditions. The very small deviations from average values of daphnite mole fractions in chlorite from the pyrite-pyrrhotite-magnetite-bearing assemblages (X = 0.41 + or - 0.03, n = 3, at Anderson Lake and 0.35 + or - 0.02, n = 8, at Stall Lake) demonstrates that fugacities of both oxygen and sulfur were buffered by pyrite, pyrrhotite, and magnetite.Intersection of chlorite and sphalerite isopleths gives peak metamorphic conditions of 6.5 to 7.0 kb and 580 degrees to 600 degrees C. Such high pressures are incompatible with metamorphic assemblages. The intersection of chlorite isopleths with Holdaway9s (1971) sillimanite-kyanite phase boundary indicates peak metamorphic pressure and temperature to be 5.6 kb and 580 degrees C, in excellent agreement with a previous estimate of 5.5 kb and 600 degrees C by Froese and Gasparrini (1975).Chlorite isopleths in P-T space are very steep and, therefore, sensitive to variations in temperature. P-T-X daphnite diagrams have potential for geothermometry, particularly when combined with other experimentally reversed equilibria defining reactions on a petrogenetic grid.

Comparisons of the growth in tissue culture of primary and metastatic melanoma

Tissue culture studies using monolayer cultures or semi-solid cultures under hypoxic or ambient oxygen conditions were carried out in 86 primary and 241 metastatic human melanomas. The frequencies with which growth occurred were similar for primary and metastatic tumours for each of the culture systems. In tumours which grew in hypoxic semi-solid culture, however, the plating efficiency (numbers of colonies per 5 X 10(5) cells plated) was significantly higher (26.1 +/- 2.8) for metastatic melanomas than for primaries (11.9 +/- 1.4). Paired comparisons of the growth of individual tumours in hypoxic cultures with growth in ambient oxygen cultures confirmed earlier observations that growth was enhanced by hypoxia due to recruitment of additional colony-forming cells. The numbers of cells recruited under hypoxic conditions were significantly greater for metastatic tumours than for primaries.

Theory of fire and fire processes

AbstractThere are two major fire processes, an understanding of which is essential for effective fire safety design: (1) the conditions under which a combustible material may become involved in flaming combustion, and (2) the rate at which such a material, once involved, will provide an output of heat, smoke, toxic gases, etc., which can endanger people and property. The first process may be regarded as covering both ignition and spread of fire on materials; its complement is the way in which fire may become extinguished. It is necessary for such processes to bring in a characteristic of the basic combustion reaction which, directly or indirectly, expresses the reactivity of the combustion process. Thus pilot ignition is usually associated with an approximate surface fuel temperature. More basically, it is associated with a critical flow rate of volatiles and a critical heat loss from the flame, the latter being influenced by ambient oxygen and temperatures conditions as well as heat lost and gained by the fuel itself. The most important factor governing the production of dangerous product is the rate at which volatiles first (fuel controlled fires) and later air (air controlled fires) are fed into the flames. The reactivity is of less importance, although it may be one of the factors which control combustion efficiency. In general, the more efficient is the combustion the more heat is produced, but the less smoke and toxic gases are produced. Some of the main advances in the above areas are reviewed in this paper.

Involvement of FMN and phenobarbital cytochrome P-450 in stimulating a one-electron reductive denitrosation of 1-(2-chloroethyl)-3-(cyclohexyl)-1-nitrosourea catalyzed by NADPH-cytochrome P-450 reductase.

Purified hepatic NADPH-cytochrome P-450 reductase, which was reconstituted with dilauroylphosphatidylcholine, catalyzed a one-electron reductive denitrosation of 1-(2-[14C]-chloroethyl)-3-(cyclohexyl)-1-nitrosourea ([14C]CCNU) to give 1-(2-[14C]-chloroethyl)-3-(cyclohexyl)urea at the expense of NADPH. Ambient oxygen or anoxic conditions did not alter the rates of [14C]CCNU denitrosation catalyzed by NADPH-cytochrome P-450 reductase with NADPH. Electron equivalents for reduction could be supplied by NADPH or sodium dithionite. However, the turnover number with NADPH was slightly greater than with sodium dithionite. Enzymatic denitrosation with sodium dithionite or NADPH was observed in anaerobic incubation mixtures which contained NADPH-cytochrome P-450 reductase with or without cytochrome P-450 purified from livers of phenobarbital (PB)-treated rats; PB cytochrome P-450 alone did not support catalysis. PB cytochrome P-450 stimulated reductase activity at molar concentrations approximately equal to or less than NADPH-cytochrome P-450 reductase concentration, but PB cytochrome P-450 concentrations greater than NADPH-cytochrome P-450 reductase inhibited catalytic denitrosation. Cytochrome c, FMN, and riboflavin demonstrated different degrees of stimulation of NADPH-cytochrome P-450 reductase-dependent denitrosation. Of the flavins tested, FMN demonstrated greater stimulation than riboflavin and FAD had no observable effect. A 3-fold stimulation by FMN was not observed in the absence of NADPH-cytochrome P-450 reductase. These studies provided evidence which establish NADPH-cytochrome P-450 reductase rather than PB cytochrome P-450 as the enzyme in the hepatic endoplasmic reticulum responsible for CCNU reductive metabolism.

Comparative physical and physiological performance of rainbow trout, Salmo gairdneri, of distinct lactate dehydrogenase B 2 phenotypes

1. 1. Adult rainbow trout ( Salmo gairdneri) LDH B 2B 2 phenotype exhibited lower swimming performance at low ambient oxygen levels than B 2'B 2' and B 2'B 2 phenotypes. 2. 2. Under decreasing oxygen conditions the oxygen consumption rate and ambient oxygen concentration at fatigue for the B 2B 2 females was significantly higher than B 2'B 2' females for the former and all other male and female phenotypes for the latter. 3. 3. Blood pO 2 at fatigue under low ambient oxygen conditions was significantly higher for females than males.