Oxygen, oxidases, and the essential trace metals

The dominant function of dioxygen as the terminal electron acceptor in aerobic systems is well established; the roles of iron and copper in the terminal oxidases are less well understood. The minor, but crucial, part that dioxygen plays in other biological processes has recently attracted much attention. The chemistry of the reduction products of dioxygen is described and the possible relation of these products to the toxic properties of dioxygen is discussed. It is suggested that the uncontrolled reaction of dioxygen with reduced species, to give the superoxide ion, hydrogen peroxide, the hydroxyl radical and perhaps other entities derived from these, is potentially hazardous to the organism. Defences exist against these species, not least in the dismutases dependent on copper-zinc, manganese and iron, in catalase and in the selenium-dependent peroxidase. The effectiveness of these defences is examined and their reduction products of dioxygen during phagocytosis is discussed.     

Oxygen Uptake and Photosynthesis of the Red Macroalga, Chondrus crispus, in Seawater: Effects of Oxygen Concentration

With an experimental system developed for aquatic plants using the mass spectrometry technique and infrared gas analysis of CO₂, we studied the responses to various O₂ concentrations of gas exchanges with the red macroalga Chondrus crispus S. The results were as follows. (a) Irrespective of the CO₂ concentration, net photosynthesis was O₂ sensitive with a 45 to 70% stimulation at 2% O₂. Even with high CO₂, a significant Warburg effect was detected. (b) Although photosynthesis was CO₂ sensitive, O₂ photoconsumption was only weakly affected by CO₂ even at high CO₂ where it was still photodependent. (c) O₂ photoconsumption was always sensitive to O₂ concentration whatever the CO₂ concentration, but with O₂ exceeding 20% the kinetics disagreed with the Michaelis-Menten model, with saturation being reached more rapidly. With various CO₂ concentrations, the apparent K_m (O₂) ranged from 4 to 16% O₂ with a relatively constant V_max (O₂) of about one-third the V_max (CO₂). (d) Dark respiration seemed to be O₂ insensitive. These results are discussed in relation to the nature of the processes able to consume O₂ in the light, and seem to be consistent with a significant involvement of a Mehlertype reaction.     

Oxygen radicals, inflammation, and tissue injury

Inflammatory reactions often result in the activation and recruitment of phagocytic cells (e.g., neutrophils and/or tissue macrophages) whose products result in injury to the tissue. In killing of endothelial cells by activated neutrophils as well as in lung injury produced by either activated neutrophils or activated macrophages there is evidence that H2O2 and iron play a role. HO. may be a key oxygen product related to the process of injury. Endothelial cells in some vascular compartments may be susceptible to neutrophil mediated injury in a manner that is independent of oxygen radicals. On the basis of in vitro observations, a synergy exits between platelets and neutrophils, resulting in enhanced oxygen radical formation by the latter. Finally, the cytokines, interleukin 1 and tumor necrosis factor, released from macrophages have both direct stimulatory effects on oxygen radical formation in neutrophils and can "prime" macrophages for enhanced oxygen radical responses to other agonists. Cytokines may also alter endothelial cells rendering them more susceptible to oxygen radical mediated injury by neutrophils. This suggests a complex network of interactions between phagocytic cells and peptide mediators, the result of which is acute, oxygen radical mediated tissue injury.     

Oxygen, the NifA gene, Nodule Structure and the Initiation of Nitrogen Fixation

Both nitrogenase and the NifA gene, which controls the expressionof the nitrogenase enzyme, require microaerobic conditions inthe infected zone of a nodule. Such conditions depend on theability of the respiratory system to consume oxygen at approximatelythe maximum rate at which it can enter that region by diffusion.The balance between consumption and supply governs the minimumsize of a functional nodule. The nature of this balance is exploredin this paper using a model. It shows that it appears physicallyimpossible for legume root nodules, below a certain minimumsize, to fix nitrogen. Furthermore, experimental data are usedto suggest that the alternative oxidase respiratory systemsmay initially provide the large respiratory capacity requiredto create microaerobic conditions, suitable for the NifA geneand nitrogenase. Nitrogen fixation, NifA gene, diffusion resistance, oxygen     

线粒体，活性氧和细胞凋亡

在能量代谢和自由基代谢中,线粒体均占据着十分重要的地位.通过呼吸链电子漏途径,线粒体产生大量超氧阴离子,并通过链式反应形成对机体有损伤作用的活性氧.通过呼吸链电子漏,氧化磷酸化解偶联,线粒体内膜产生通透性转变孔道（PTP）及Box-和/或PTP-介导的细胞色素c向胞质的转移等种种因素,线粒体参与一般抗氧化防御及细胞凋亡等重要生理过程的调控.在与线粒体相关的细胞凋亡中,活性氧的信号作用是十分明显的.     

Oxygen consumption of the lobster,Homarus americanus milne-edwards

Summary 1. Oxygen consumption by a group of 25 lobsters was essentially constant over a range of ambient oxygen concentrations from 1.0 to 8.5 mg/l. Consumption by groups of 35 and 50 lobsters at 15° C decreased as the concentration decreased.2. Oxygen consumption by individuals at 10° and 15° C increased as the oxygen concentration increased.3. Oxygen consumption increased as activity increased with crowding.4. Oxygen consumption almost doubled after feeding.5. Oxygen consumption per unit weight decreased with increasing size.6. The average rate of oxygen consumption by individuals doubled over the temperature range 12° to 25° C.7. Oxygen consumption in air at 6° to 25° C was much less than in water.

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Sauerstoffverbrauch des HummersHomarus americanus Milne-Edwards

Kurzfassung Bei einer Gruppe von 25 Hummern wurde der Sauerstoffverbrauch in Dauerfluß-Respirometern gemessen. Bei 10° C erwies er sich als im wesentlichen konstant über einen Bereich der Sauerstoffkonzentration im umgebenden Wasser von 1,0 bis 8,5 mg/l. Bei Gruppen von 35 und 50 Hummern, welche bei 15° C getestet wurden, nahm der Sauerstoffverbrauch jedoch mit fallender Sauerstoffkonzentration etwas ab. Anstieg der Individuenzahl pro Raumeinheit (crowding) führte zu steigender Bewegungsaktivität und zu erhöhtem Sauerstoffverbrauch. Nahrungsaufnahme verursachte fast eine Verdoppelung des Sauerstoffverbrauchs. Kleine Individuen verbrauchen pro Gewichtseinheit mehr Sauerstoff als große. In manometrischen Respirometern stieg der Sauerstoffverbrauch bei hohen Sauerstoffkonzentrationen im umgebenden Wasser mit der Temperatur. Bei 6° bis 25° C war der Sauerstoffverbrauch in der Luft wesentlich geringer als im Wasser.

     

Radio Telemetry of the Electrocardiogram,Fitness Tests,and Oxygen Uptake of Water-Polo Players

During competitive water polo, heart rate in six subjects was monitored by cupped plastic and silver electrodes glued to the skin. Minimum rates during the game averaged 156 beats/min.; maximum rates averaged 186 beats/min. Mean maximum rate with bicycle exercise was 188 beats/min. Maximum oxygen (VO₂ max.) with bicycle exercise of 14 water-polo players was 53.3 ml./kg. Physical working capacity (PWC 170) was 1310 kilopond metres per square metre (k.p.m./sq.m.). PWC 170 correlated well with VO₂ max. in this small group (r = 0.77).Oxygen uptake was measured at three speeds of swimming and four levels of work on a bicycle ergometer. VO₂ max. of swimming was 88% of that obtained on bicycle exercise. The slope of the oxygen uptake vs. pulse rate curves was less for the swimming than for cycling, so that for a given oxygen uptake below the maximal, pulse rate was less in the swimmers. At near-maximal swimming, respiratory quotient was 0.95 compared with 1.27 for cycling, suggesting that the swimmers were underbreathing.     

Oxygen Evolution and Oxygen Uptake by Isolated Chloroplasts of Wheat Irradiated with Monochromatic Light, without the Addition of an Oxidant

The oxygen exchange obtained when isolated chloroplasts of wheat are irradiated, without the addition of a Hill oxidant, has been investigated. Depending on the wavelength, two types of oxygen exchange are obtained. In light absorbed by both photosystems an oxygen gush appears directly upon irradiation. This oxygen evolving reaction is soon replaced by an oxygen uptake which is present until the end of the irradiation period. In light absorbed mainly in photosystem I, no oxygen gush can be observed, instead an oxygen uptake appears directly upon irradiation. An oxygen evolving process can also be observed in irradiations performed with photo-system I light, but this process appears after 10–15 seconds of irradiation. The influence of various external factors on the oxygen gush and the oxygen uptake, e.g. different wavelengths, light intensity, length of the dark periods between irradiations, was studied. The results show that the oxygen evolving reaction appearing upon irradiation with light absorbed by photosystem II and I, reflect the reduction of an oxidant, probably plasto-quinone, in the electron transport chain between the two photosystems. The reoxidation of this oxidant can be brought about after irradiating with light absorbed in photosystem I, or by prolonging the dark period between irradiations, or through some unknown process connected to photosystem II. The oxygen uptake which consists of two components, one appearing directly upon irradiation and the other one appearing after about 10 seconds of irradiation, confirms earlier observations that oxygen can be reduced in photosystem I. The electrons for the oxygen uptake appearing directly upon irradiation, are obtained from the reduced intermediates in the electron transport chain between the two photosystems. The electrons for the other oxygen uptake process are obtained from a reductant in the chloroplasts with access to the carrier chain between the photosystems. Whether the two oxygen uptake reactions reflect two sites of interaction of oxygen with the electron transport chain or only one site is discussed.