Geological constraints on the origin of oxygenic photosynthesis

This article examines the geological evidence for the rise of atmospheric oxygen and the origin of oxygenic photosynthesis. The evidence for the rise of atmospheric oxygen places a minimum time constraint before which oxygenic photosynthesis must have developed, and was subsequently established as the primary control on the atmospheric oxygen level. The geological evidence places the global rise of atmospheric oxygen, termed the Great Oxidation Event (GOE), between ~2.45 and ~2.32 Ga, and it is captured within the Duitschland Formation, which shows a transition from mass-independent to mass-dependent sulfur isotope fractionation. The rise of atmospheric oxygen during this interval is closely associated with a number of environmental changes, such as glaciations and intense continental weathering, and led to dramatic changes in the oxidation state of the ocean and the seawater inventory of transition elements. There are other features of the geologic record predating the GOE by as much as 200–300 million years, perhaps extending as far back as the Mesoarchean–Neoarchean boundary at 2.8 Ga, that suggest the presence of low level, transient or local, oxygenation. If verified, these features would not only imply an earlier origin for oxygenic photosynthesis, but also require a mechanism to decouple oxygen production from oxidation of Earth’s surface environments. Most hypotheses for the GOE suggest that oxygen production by oxygenic photosynthesis is a precondition for the rise of oxygen, but that a synchronous change in atmospheric oxygen level is not required by the onset of this oxygen source. The potential lag-time in the response of Earth surface environments is related to the way that oxygen sinks, such as reduced Fe and sulfur compounds, respond to oxygen production. Changes in oxygen level imply an imbalance in the sources and sinks for oxygen. Changes in the cycling of oxygen have occurred at various times before and after the GOE, and do not appear to require corresponding changes in the intensity of oxygenic photosynthesis. The available geological constraints for these changes do not, however, disallow a direct role for this metabolism. The geological evidence for early oxygen and hypotheses for the controls on oxygen level are the basis for the interpretation of photosynthetic oxygen production as examined in this review.     

Effect of partial oxygen pressure on survival, proliferation, and differentiation of mouse bone marrow mesenchymal stem cells

Effects of partial oxygen pressure in a gas mixture surrounding the culture medium on survival, proliferation and differentiation of mesenchymal stem cells (MSC) isolated from mouse bone marrow was studied. It was found that 3% oxygen increased the survival of cells seeded at low density; the rate and duration of the MSC proliferation were also elevated. Effect of oxygen concentration on replicative activity of MSC was manifested as early as the first few days after the onset of cell growth. Studies of colony formation revealed that preincubation of cells with 21% oxygen had a negative effect on cell growth under 3% oxygen, while preincubation with 3% oxygen stimulated MSC proliferation in the presence of 21% oxygen. Notwithstanding, this effect of oxygen cannot be interpreted as unequivocally deleterious. Low partial oxygen pressure inhibited osteogenic differentiation of MSC, but adipogenic differentiation was insensitive to oxygen concentration. It is concluded that proliferation and differentiation of MSC depend critically on oxygen content in the culture medium.     

Effects of Fiber Type and Size on the Heterogeneity of Oxygen Distribution in Exercising Skeletal Muscle

The process of oxygen delivery from capillary to muscle fiber is essential for a tissue with variable oxygen demand, such as skeletal muscle. Oxygen distribution in exercising skeletal muscle is regulated by convective oxygen transport in the blood vessels, oxygen diffusion and consumption in the tissue. Spatial heterogeneities in oxygen supply, such as microvascular architecture and hemodynamic variables, had been observed experimentally and their marked effects on oxygen exchange had been confirmed using mathematical models. In this study, we investigate the effects of heterogeneities in oxygen demand on tissue oxygenation distribution using a multiscale oxygen transport model. Muscles are composed of different ratios of the various fiber types. Each fiber type has characteristic values of several parameters, including fiber size, oxygen consumption, myoglobin concentration, and oxygen diffusivity. Using experimentally measured parameters for different fiber types and applying them to the rat extensor digitorum longus muscle, we evaluated the effects of heterogeneous fiber size and fiber type properties on the oxygen distribution profile. Our simulation results suggest a marked increase in spatial heterogeneity of oxygen due to fiber size distribution in a mixed muscle. Our simulations also suggest that the combined effects of fiber type properties, except size, do not contribute significantly to the tissue oxygen spatial heterogeneity. However, the incorporation of the difference in oxygen consumption rates of different fiber types alone causes higher oxygen heterogeneity compared to control cases with uniform fiber properties. In contrast, incorporating variation in other fiber type-specific properties, such as myoglobin concentration, causes little change in spatial tissue oxygenation profiles.     

The steady-state transport of oxygen through hemoglobin solutions

The steady-state transport of oxygen through hemoglobin solutions was studied to identify the mechanism of the diffusion augmentation observed at low oxygen tensions. A novel technique employing a platinum-silver oxygen electrode was developed to measure the effective diffusion coefficient of oxygen in steady-state transport. The measurements were made over a wider range of hemoglobin and oxygen concentrations than previously reported. Values of the Brownian motion diffusion coefficient of oxygen in hemoglobin solution were obtained as well as measurements of facilitated transport at low oxygen tensions. Transport rates up to ten times greater than ordinary diffusion rates were found. Predictions of oxygen flux were made assuming that the oxyhemoglobin transport coefficient was equal to the Brownian motion diffusivity which was measured in a separate set of experiments. The close correlation between prediction and experiment indicates that the diffusion of oxyhemoglobin is the mechanism by which steady-state oxygen transport is facilitated.     

Studies on reactions of illuminated chloroplasts. III. Simultaneous photoproduction and consumption of oxygen studied with oxygen isotopes

The evolution of oxygen, as in a typical Hill reaction, during periods of net oxygen consumption by illuminated chloroplasts has been demonstrated through kinetic studies with oxygen isotopes. The ability of molecular oxygen to function as a Hill oxidant is thus confirmed.     

The influence of oxygen supply on metabolism of neural cells cultured on a gas‐permeable PTFE foil

The influence of oxygen on neural stem cell proliferation, differentiation, and apoptosis is of great interest for regenerative therapies in neurodegenerative disorders, such as Parkinson's disease. These oxygen depending mechanisms have to been considered for the optimization of neural cell culture conditions. In this study, we used a cell culture system with an oxygen‐permeable polytetrafluorethylene (PTFE) foil to investigate the effect of oxygen on metabolism and survival of neural cell lines in vitro. Human glial astrocytoma‐derived cells (GOS‐3) and rat pheochromacytoma cells (PC12) were cultured on the gas‐permeable PTFE foil as well as a conventional non oxygen‐permeable cell culture substrate at various oxygen concentrations. Analyses of metabolic activity, gene expression of apoptotic grade, and dopamine synthesis were performed. Under low oxygen partial pressure (2%, 5%) the anaerobic metabolism and apoptotic rate of cultured cells is diminished on PTFE foil when compared with the conventional culture dishes. In contrast, under higher oxygen atmosphere (21%) the number of apoptotic cells on the PTFE foil was enhanced. This culture model demonstrates a suitable model for the improvement of oxygen dependent metabolism under low oxygen conditions as well as for induction of oxidative stress by high oxygen atmosphere without supplementation of neurotoxins. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

Effect of nitrite-induced methemoglobinemia on the kinetics of blood deoxygenation

Kinetics of blood deoxygenation was studied during acute hypoxia induced by subcutaneous administration of sodium nitrite using polarographic method. Plasma oxygen tension remained unaltered as the dose of sodium nitrite increased, while the dynamics of oxygen release was dose-dependent. The constant of oxyhemoglobin deoxygenation rate proved to vary with blood deoxygenation. The nitrite-induced deceleration of oxyhemoglobin deoxygenation was due to the inactivation of a fraction of hemoglobin as well as to the increased hemoglobin oxygen affinity and possible changes in the oxygen permeability of erythrocyte membranes during acute methemoglobinemia.     

The effect of inspired oxygen concentration on the ventilation-perfusion distribution in inhomogeneous lungs

The coupled conservation of mass equations for oxygen, carbon dioxide and nitrogen are written down for a lung model consisting of two homogeneous alveolar compartments (with different ventilation-perfusion ratios) and a shunt compartment. As inspired oxygen concentration and oxygen consumption are varied, the flux of oxygen, carbon dioxide and nitrogen across the alveolar membrane in each compartment varies. The result of this is that the expired ventilation-perfusion ratio for each compartment becomes a function of inspired oxygen concentration and oxygen consumption as well as parameters such as inspired ventilation and alveolar perfusion. Another result is that the "inspired ventilation-perfusion ratio and the "expired ventilation-perfusion ratio differ significantly, under some conditions, for poorly ventilated lung compartments. As a consequence, we need to distinguish between the "inspired ventilation-perfusion distribution, which is independent of inspired oxygen concentration and oxygen consumption, and the "expired ventilation-perfusion distribution, which we now show to be strongly dependent on inspired oxygen concentration and less dependent oxygen consumption. Since the multiple inert gas elimination technique (MIGET) estimates the "expired ventilation-perfusion distribution, it follows that the distribution recovered by MIGET may be strongly dependent on inspired oxygen concentration.     

高氧在临床应用中的研究进展

氧气是人类赖以生存的物质,是人体进行新陈代谢的关键,是人体生命活动的第一需要。在人类没有发现氧气之前,其对人类生存的重要性并不为人类所知。随着人类发现氧气并意识到其对人类生存的重要性之后,人类对氧气的研究越来越深入。起初,吸入高浓度氧仅用来治疗低氧血症等呼吸相关疾病,而后,氧气发展成为临床常用的一种辅助治疗手段,可用于多个科室多种疾病的辅助治疗。本研究小组通过动物实验发现高浓度氧吸入可明显降低脓毒症小鼠的病死率,并可以改善其组织病理,炎性细胞因子等的表达变化,也可以改善脑缺血再灌注小鼠的脑梗死面积及行为学表现等。本文主要概括了高浓度氧吸入对于全身各系统的影响作用并重点阐述了高浓度氧吸入对于脓毒症以及组织缺血再灌注的治疗作用。     

Measurement of low levels of oxygen and their effect on respiration in cell suspensions maintained in an open system

The presence of low levels of oxygen may have profound effects on the cytotoxic activity of radiation, radiosensitizers, and bioreductive alkylating agents. As others have shown, low oxygen tensions may significantly alter rates of cellular and chemical oxygen consumption. When experiments are performed at very low oxygen concentrations, the opposing effects of oxygen leakage into and cellular/chemical oxygen consumption from the system can lead to unpredictable results. Use of a newly designed, highly sensitive Clark-type oxygen sensor has permitted accurate and reproducible measurement of low levels of oxygen. Cellular depletion of oxygen at various cell densities has been monitored for a series of oxygen tensions in solution and the corresponding respiration rates have been calculated. Although oxygen depletion was found to be quite significant at low oxygen tensions, not all oxygen present could be removed by cellular respiration. Respiration rate decreased as oxygen tension decreased and approached zero at low oxygen tensions. This result was independent of cell density. A model is presented to account for the observed effect of oxygen tension on cellular oxygen utilization.     

Oxygen consumption during septic shock. Effects of inotropic drugs

Septic shock may be defined as a clinical entity wherein a patient has an inadequate peripheral metabolism in the presence of circulating bacteria. The demands for metabolic requirements of the tissues and hence for oxygen transport to these tissues are then markedly high. The average response to increased metabolism in such patients is a percentage increase in cardiac output that is comparable to the percentage increase in oxygen consumption while oxygen extraction rate does not change or even decreases in severe or/and advanced septic shock. This emphasizes the high priority placed by the body on the ability to increase blood flow from the heart in the presence of increased metabolic demands due to sepsis. Concerning the myocardium, oxygen consumption is low in hyper- and hypodynamic states of septic shock, probably and partially due to marked arterial vasodilatation. However, in hypodynamic states, the lower value of perfusion pressure may account for a decrease in myocardial oxygen supply, especially in subendocardial areas and may be responsible for myocardial ischaemia, more especially as myocardial oxygen extraction as well as systemic oxygen extraction is impaired. The goal of therapeutics is to improve oxygen availability through: (1) maintenance of haemoglobin levels and (2) increases in stroke volume using inotropic drugs since these drugs may produce a rise in myocardial oxygen supply higher than their drug-induced increase in oxygen requirements in hypodynamic states of septic shock.     

Effect of proline on the production of singlet oxygen

Molecular oxygen in electronic singlet state is a very powerful oxidant. Its damaging action in a variety of biological processes has been well recognized. Here we report the singlet oxygen quenching action of proline. Singlet oxygen (1O2) was produced photochemically by irradiating a solution of sensitiser and detected by following the formation of stable nitroxide radical yielded in the reaction of 1O2 with the sterically hindered amine (2,2,6,6-tetramethylpiperidine, TEMP). Illumination of a sensitiser, toluidine blue led to a time dependent increase in singlet oxygen production as detected by the formation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) by EPR spectrometry. Interestingly, the production of TEMPO was completely abolished by the presence of proline at concentration as low as 20mM. These results show that proline is a very effective singlet oxygen quencher. Other singlet oxygen generating photosensitizer like hematopophyrin and fluorescein also produced identical results with proline. Since proline is one of the important solutes which accumulate in many organisms when they are exposed to environmental stresses, it is likely that proline accumulation is related to the protection of these organisms against singlet oxygen production during stress conditions. A possible mechanism of singlet oxygen quenching by proline is discussed.     

氧载体对L—天冬酰胺酶发酵过程影响的研究

以抗癌药物Ｌ天冬酰胺酶生产为应用背景,针对发酵过程中存在严重耗氧问题,研究了氧载体对发酵过程的影响。通过对几种氧载体的筛选,认为正十二烷最适合于该发酵过程。随后以产物Ｌ天冬酰胺酶活性、菌体浓度以及溶氧水平为主要指标,考察了氧载体在发酵过程中的作用,实验表明,发酵基质中５％正十二烷的添加量为最佳浓度,这种氧载体的加入,明显地提高了发酵介质中的溶氧水平,改善了供氧条件,增加了菌体浓度,提高了Ｌ天冬酰胺酶发酵水平,在优化条件下,可使发酵液最终酶活提高２１％左右     

Exploring the Radial and Longitudinal Aeration of Primary Maize Roots by Means of Clark-Type Oxygen Microelectrodes

Clark-type oxygen microelectrodes were used to measure the radial and longitudinal oxygen distribution in aerenchymatous and nonaerenchymatous primary roots of intact maize seedlings. A radial intake of oxygen from the rooting medium was restricted by embedding the roots in 1% agar causing aeration to be largely dependent upon longitudinal internal transport from the shoot. In both root types, oxygen concentrations declined with distance from the base, and were lower in the stele than in the cortex. Also, the bulk of the oxygen demand was met internally by transport from the shoots, but a little oxygen was received by radial inward diffusion from the surrounding agar, and in some positions the hypodermal layers received oxygen from both the agar and the cortex. Near to the base, the oxygen partial pressure difference between the cortex and the center of the stele could be as much as 6–8 kPa. Nearer to the tip, the differences were smaller but equally significant. In the nonaerenchymatous roots, cortical oxygen partial pressures near the apex were becoming very low (< 1 kPa) as root lengths approached 100 mm, and towards the center of the stele values reached 0.1 kPa or lower. However, the data indicated that respiratory activity did not decline until the cortical oxygen pressure was less than 2 kPa. Mathematical modeling based on Michaelis–Menten kinetics supported this and suggested that the respiratory decline would be mostly restricted to the stele until cortical oxygen pressures approached very low values. At a cortical oxygen pressure of 0.75 kPa, it was shown that respiratory activity in the pericycle and phloem might remain as high as 80–100% of maximum even though in the center of the stele it could be less than 1% of maximum. Aerenchyma production resulted in increases in oxygen concentration throughout the roots with cortical partial pressures of ca. 5–6 kPa and stelar values of ca. 3–4 kPa near the tips of 100 mm long roots. In aerenchymatous roots, there was some evidence of a decline in the oxygen permeability of the epidermal–hypodermal cylinder close to the apex; a decline in stelar oxygen permeability near the base was indicated for both root types. There was some evidence that the mesocotyl and coleoptile represented a very significant resistance to oxygen transport to the root.     

Reactive oxygen and ischemia/reperfusion injury of the liver

Pharmacological experiments suggested that reactive oxygen species contribute to ischemia-reperfusion injury of the liver. Since there is no evidence that quantitatively sufficient amounts of reactive oxygen are generated intracellularly to overwhelm the strong antioxidant defense mechanisms in the liver and cause parenchymal cell injury, the role of reactive oxygen in the pathogenesis remains controversial. This paper reviews the data and conclusions obtained with pharmacological intervention studies in vivo, the sources of reactive oxygen in the liver as well as the growing evidence for the importance of liver macrophages (Kupffer cells) and infiltrating neutrophils in the pathogenesis. A comprehensive hypothesis is presented that focuses on the extracellular generation of reactive oxygen in the hepatic sinusoids, where Kupffer cell-derived reactive oxygen species seem to be involved in the initial vascular and parenchymal cell injury and indirectly also in the recruitment of neutrophils into the liver. Reactive oxygen species may also contribute to the subsequent neutrophil-dependent injury phase as one of the toxic mediators released by these inflammatory cells.     

The structural basis for anthracycline antibiotic stimulation of oxygen consumption by HL-60 cells and mitochondria

The effects of anthracyclines on the stimulation of oxygen consumption in the presence of HL-60 cell sonicates, beef heart mitochondria and NADPH cytochrome c reductase were determined as a measure of oxygen radical production. Drug-induced oxygen radical formation in each of these systems was modulated by structural changes in the aglycone as well as in the amino sugar portion of the anthracycline molecule. Cytotoxic potency was not correlated with anthracycline-induced oxygen consumption, suggesting that net oxygen radical production was not the primary factor in tumor cell killing by anthracyclines. In contrast, available data on anthracycline cardiotoxicity appeared to correlate with the drug-induced stimulation of oxygen consumption by beef heart mitochondria, providing support for the premise that drug-induced oxygen radicals formed in the presence of mitochondrial flavoproteins are involved in the adverse effects of anthracyclines on the heart. Cyanomorpholinoadriamycin, an analogue which is 100 to 1000 times more potent than adriamycin (doxorubicin) as an antineoplastic agent, has been shown here and elsewhere to be equivalent to adriamycin in stimulating oxygen radical production by beef heart mitochondria and to produce similar cardiotoxicity at equimolar concentrations. Thus, it appears possible to separate the favorable antitumor activity of adriamycin from its unwanted cardiotoxicity by structural changes such as substitution of the antibiotic by a cyanomorpholino moiety.     

Influence of the intensity of oxygen mass transfer on the biosynthesis of amphotericin B

Influence of oxygen mass transfer intensity characterized by the rate of oxygen dissolution (S) and the agitation rate (n), as well as influence of dissolved oxygen concentration on the process of amphotericin B biosynthesis was studied. It was shown that S = 40 and 110 mg/l. min and n = 450 and 800 min-1 were respectively the lower and the upper levels of the optimal conditions by oxygen mass transfer during amphotericin B biosynthesis. When biosynthesis of amphotericin B was conducted under conditions of the optimal oxygen mass transfer, the dissolved oxygen concentration of about 12 to 15 per cent of the saturation level was critical for the culture respiration. Inhibition of the culture respiration and antibiotic synthesis was induced under conditions of increased oxygen mass transfer intensity (S greater than 110 mg/l. min and n greater than 800 min-1) by high intensity mechanical agitation of the fermentation broth. Under conditions of decreased oxygen mass transfer (S less than 40 mg/l. min and n = less than 450 min-1) it was induced by insufficient supply of oxygen to the culture. On the basis of the results it was shown possible to control the aeration and agitation conditions by the rate of oxygen uptake and dissolved oxygen concentration. The data should be considered in optimization of aeration and agitation conditions in biosynthesis of amphotericin B in large fermenters.     

Aroma Components of Fresh Sugar Cane Juice

To study the behavior of Bifidobacterium toward oxygen, oxygen uptake was investigated in detail. The cells of Bifidobacterial strains absorbed considerable amounts of oxygen. The exogenous oxygen uptake activity changed depending upon the period of incubation. Bifidobacterial cells also had high endogenous oxygen uptake, which was, in B. longum strains, as high as about 80% of the exogenous oxygen uptake activity. Bifidobacterial cells accumulated considerable amounts of polysaccharide, which was associated with cellular growth. By incubating the cultivated cells in a glucose-free medium, the endogenous oxygen uptake activity was decreased with a decrease of intracellular polysaccharide. Therefore it was postulated that the high endogenous oxygen uptake activity of Bifidobacterium was owing to the metabolism of intracellular polysaccharide. The enzymatic activity, which was involved in the mechanism of oxygen uptake, was also investigated.