Quantitative aspects of oxygen and carbon dioxide exchange through the lungs in Ocypode ceratophthalmus (Crustacea: Decapoda) during rest and exercise in water and air

Ghost crabs Ocypode ceratophthalmus were exercised in air and water to measure CO₂ and O₂ exchange rates using the method of instantaneous measurements of oxygen consumption rate (MO₂) where applicable. Average heart rate increased from 100 to nearly 400 pulses per minute after five minutes of exercise on a treadmill at a run rate of 0.133 m s^?1. It took less than a minute for oxygen taken up through the lung epithelium from the air inside the branchial cavity to reach the maximal oxygen consumption rate of 26.1 mmol O₂ kg^?1 h^?1. Resting MO₂ was 4.06 mmol O₂ kg^?1 h^?1 in air, but decreased to 3.37 mmol O₂ kg^?1 h^?1 in seawater. Radioactive CO₂ from injected l-lactate is released linearly by the lung. The percent accumulated 14-CO₂ in exhaled air, plotted against time, intersects zero time on the x -axis, indicating rapid gas exchange at the lung surface. The P ₅₀ values for native haemocyanin of 4.89 mm Hg before exercise, and 8.99 mm Hg after exercise, are typical of a high-affinity haemocyanin usually associated with terrestrial crabs. The current notion that Ocypode ceratophthalmus drown when submerged in seawater was not substantiated by our experiments. MO₂ in seawater increased from 3.37 mmol O₂ kg^?1 h^?1 for resting crabs to 5.72 mmol O₂ kg^?1 h^?1 during exercise. When submerged by wave-seawater in the natural environment and during exercise in respirometer-seawater O. ceratophthalmus do not swim but, having a specific density of 1.044, float nearly weightless with a minimum of body movements.     

Acclimation of photosynthesis to increasing atmospheric CO2: The gas exchange perspective

The nature of photosynthetic acclimation to elevated CO₂ is evaluated from the results of over 40 studies focusing on the effect of long-term CO₂ enrichment on the short-term response of photosynthesis to intercellular CO₂ (the A/C_i response). The effect of CO₂ enrichment on the A/C_i response was dependent on growth conditions, with plants grown in small pots (< 5 L) or low nutrients usually exhibiting a reduction of A at a given C_i, while plants grown without nutrient deficiency in large pots or in the field tended to exhibit either little reduction or an enhancement of A at a given C_i following a doubling or tripling of atmospheric CO₂ during growth. Using theoretical interpretations of A/C_i curves to assess acclimation, it was found that when pot size or nutrient deficiency was not a factor, changes in the shape of A/C_i curves which are indicative of a reallocation of resources within the photosynthetic apparatus typically were not observed. Long-term CO₂ enrichment usually had little effect or increased the value of A at all C_i. However, a minority of species grown at elevated CO₂ exhibited gas exchange responses indicative of a reduced amount of Rubisco and an enhanced capacity to metabolize photosynthetic products. This type of response was considered beneficial because it enhanced both photosynthetic capacity at high CO₂ and reduced resource investment in excessive Rubisco capacity. The ratio of intercellular to ambient CO₂ (the C_i/C_a ratio) was used to evaluate stomatal acclimation. Except under water and humidity stress, C_i/C_a exhibited no consistent change in a variety of C₃ species, indicating no stomatal acclimation. Under drought or humidity stress, C_i/C_a declined in high-CO₂ grown plants, indicating stomata will become more conservative during stress episodes in future high CO₂ environments.Abbreviations A net CO₂ assimilation rate - C_i (C_a) intercellular (ambient) partial pressure of CO₂ - operational C_i intercellular partial pressure of CO₂ at a given ambient partial pressure of CO₂ - g_s stomatal conductance - normal CO₂ current atmospheric mole fraction of CO₂ (330 to 355 mol mol^–1) - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase     

O2 Uptake in hyperthyroidism during constant work rate and incremental exercise

To investigate the effect of hyperthyroidism on the pattern and time course of O2 uptake (VO2) following the transition from rest to exercise, six patients and six healthy subjects performed cycle exercise at an average work rate (WR) of 18 and 20 W respectively. Cardiorespiratory variables were measured breath-by-breath. The patients also performed a progressively increasing WR test (1-min increments) to the limit of tolerance. Two patients repeated the studies when euthyroid. Resting and exercise steady-state (SS) VO2 (ml.kg-1.min-1) were higher in the patients than control (5.8, SD 0.9 vs 4.0, SD 0.3 and 12.1, SD 1.5 vs 10.2, SD 1.0 respectively). The increase in VO2 during the first 20 s exercise (phase I) was lower in the patients (mean 89 ml.min-1, SD 30) compared to the control (265 ml.min-1, SD 90), while the difference in half time of the subsequent (phase II) increase to the SS VO2 (patient 26 s, SD 8; controls 17 s, SD 8) were not significant (P = 0.06). The O2 cost per WR increment (delta VO2/delta WR) in ml.min-1.w-1, measured during the incremental period (mean 10.9; range 8.3-12.2), was always within two standard deviations of the normal value (10.3, SD 1). In the two patients who repeated the tests, both the increment of VO2 from rest to SS during constant WR exercise and the delta VO2/delta WRs during the progressive exercise were higher in the hyperthyroid state than during the euthyroid state.(ABSTRACT TRUNCATED AT 250 WORDS)     

Model of gas exchange and diffusion in legume nodules

A mathematical model is described which allows the estimation of rates of O₂, CO₂, N₂, and H₂ exchange from legume nodules under steady state conditions of N₂ fixation. Calculated rates of gas exchange under defined conditions of nodule size, relative growth rate (RGR), specific total nitrogenase activity (TNA), nitrogenase electron allocation coefficient (EAC), uptake-hydrogenase activity (HUP) and nature of the N export product compared favorably with experimentally-obtained rates reported in the literature. Therefore the model was used to predict the effects of varying each of these nodule characteristics on the rates of gas exchange, and on the apparent respiratory cost (CO₂/NH₃) and sucrose cost (sucrose consumed/NH₃) of N₂ fixation.The model predicted that, all other characters being equal, ureide-producing nodules would consume 8% less sucrose per N fixed than asparagine-producing nodules, but would display an apparent respiratory cost which would be 5% higher than that in asparagine-producing nodules. In both ureide-producing and asparagine-producing nodules, the major factor affecting the apparent respiratory cost of N₂ fixation was predicted to be EAC, followed by TNA, nodule RGR and nodule size. The relative importance of HUP in improving the apparent respiratory cost of N₂ fixation was predicted to be largely dependent upon its potential role in the regulation of EAC. Abbreviations: See Appendix 1.     

Modelling the CO2 gas exchange of grassland vegetation from experimental data

Pseudo-cubic spline functions were applied to the two atmospheric CO₂ concentrations of 340 and 600 l·l^–1 CO₂ for describing the average daily CO₂ gas exchange rates of simplifed grassland model ecosystems. Measurements used were from daily means of photon flux density (PhAR), temperature and relative air humidity, phytomass of each day, leaf area indexes, average phenological states of the vegetation (1–15), and water exchange rates of the entire model ecosystems. The functions were validated with, data from the same experimental year. We also succeeded in verifying the functions with the response data from years other than those used for constructing the model.     

Respiration and oxygen transport functions of the blood from an intertidal fish,Helcogramma medium (Tripterygiidae)

Synopsis Aquatic and aerial oxygen uptake (̇O₂), ventilation frequency, and oxygen transport properties of the blood were determined for the intertidal fish Helcogramma medium. Ventilation frequency increased in response to decreased environmental PO₂ and aquatic ̇O₂ was maintained down to a critical PO₂ of 30–40 mm Hg. Below PO₂ 30 mm Hg fish intermittently gulped air and finally emerged into air at PO₂ 18 mm Hg. After 1 h exposure to air ̇O₂ decreased to 60% of the aquatic rate and this was accompanied by an increase in blood lactate. Aerobic expansibility was reduced in air (×1.2) compared to water (× 5.5). The Hb concentration was 0.47 ± 0.13 mmol 1^–1 and hematocrit 11.55 ± 3.61% indicating a moderate O₂-carrying capacity. Oxygen affinity was not especially high (P₅₀ = 19 mm Hg at pH 7.7 and 15°C) and ATP was the predominant acid-soluble phosphate regulating P₅₀. The equilibrium curve was essentially hyperbolic (Hill's n = 1.2) with a marked Bohr effect = –1.06) and Root effect (saturation depressed by 50% at pH7.1). The pattern of respiration and the respiratory properties of the blood together with observations of the behaviour of the fish during aerial exposure indicated that Helcogramma is adapted to living in a well-aerated environment yet can adequately tolerate short term exposure to low aquatic PO₂ or air.     

Hyperpnoea and CO2 sensitivity of the respiratory centres during exercise

The aim of this study was to specify whether exercise hyperpnoea was related to the CO2 sensitivity of the respiratory centres measured during steady-state exercise of mild intensity. Thus, ventilation (VE), breathing pattern [tidal volume (VT), respiratory frequency (f), inspiratory time (TI), total time of the respiratory cycle (TTOT), VT/TI, TI/TTOT] and CO2 sensitivity of the respiratory centres determined by the rebreathing method were measured at rest (SCO2re) and during steady-state exercise (SCO2ex) of mild intensity [CO2 output (VCO2) = 20 ml.kg-1.min-1] in 11 sedentary male subjects (aged 20-34 years). The results showed that SCO2re and SCO2ex were not significantly different. During exercise, there was no correlation between VE and SCO2ex and, for the same VCO2, all subjects had very close VE values normalized for body mass (bm), regardless of their SCO2ex (VEbm0.75 = 1.44 l.min-1.kg-1 SD 0.10). A highly significant positive correlation between SCO2ex and VT (normalised for bm) (r = 0.80, P less than 0.01), TI (r = 0.77, P less than 0.01) and TTOT (r = 0.77, P less than 0.01) existed, as well as a highly significant negative correlation between SCO2ex and (normalised for bm-0.25) (r = -0.73, P less than 0.01). We conclude that the hyperpnoea during steady-state exercise of mild intensity is not related to the SCO2ex. The relationship between breathing pattern and SCO2ex suggests that the breathing pattern could influence the determination of the SCO2ex. This finding needs further investigation.     

The effect of exercise intensity and duration on the oxygen deficit and excess post-exercise oxygen consumption

Nine males with mean maximal oxygen consumption (VO2max) = 63.0 ml.kg-1.min-1, SD 5.7 and mean body fat = 10.6%, SD 3.1 each completed nine counterbalanced treatments comprising 20, 50 and 80 min of treadmill exercise at 30, 50 and 70% VO2max. The O2 deficit, 8 h excess post-exercise oxygen consumption (EPOC) and EPOC:O2 deficit ratio were calculated for all subjects relative to mean values obtained from 2 control days each lasting 9.3 h. The O2 deficit, which was essentially independent of exercise duration, increased significantly (P less than 0.05) with intensity such that the overall mean values for the three 30%, 50% and 70% VO2max workloads were 0.83, 1.89 and 3.09 l, respectively. While there were no significant differences (P greater than 0.05) between the three EPOCs after walking at 30% VO2max for 20 (1.01 l), 50 (1.43 l) and 80 min (1.04 l), respectively, the EPOC thereafter increased (P less than 0.05) with both intensity and duration such that the increments were much greater for the three 70% VO2max workloads (EPOC: 20 min = 5.68 l; 50 min = 10.04 l; 80 min = 14.59 l) than for the three 50% VO2max workloads (EPOC: 20 min = 3.14 l; 50 min = 5.19 l; 80 min = 6.10 l). An analysis of variance indicated that exercise intensity was the major determinant of the EPOC since it explained five times more of the EPOC variance than either exercise duration or the intensity times duration interaction. The mean EPOC:O2 deficit ratio ranged from 0.8 to 4.5 and generally increased with both exercise intensity and duration.(ABSTRACT TRUNCATED AT 250 WORDS)     

A method for estimating bicarbonate buffering of lactic acid during constant work rate exercise

A method to estimate the CO₂ derived from buffering lactic acid by HCO₃ ^– during constant work rate exercise is described. It utilizes the simultaneous continuous measurement of O₂ uptake ( O₂) and CO₂ output ( CO₂), and the muscle respiratory quotient (RQ_m). The CO₂ generated from aerobic metabolism of the contracting skeletal muscles was estimated from the product of the exercise-induced increase in O₂ and RQ_m calculated from gas exchange. By starting exercise from unloaded cycling, the increase in CO₂ stores, not accompanied by a simultaneous decrease in O₂ stores, was minimized. The total CO₂ and aerobic CO₂ outputs and, by difference, the millimoles (mmol) of lactate buffered by HCO₃ ^– (corrected for hyperventilation) were estimated. To test this method, ten normal subjects performed cycling exercise at each of two work rates for 6 min, one below the lactic acidosis threshold (LAT) (50 W for all subjects), and the other above the LAT, midway between LAT and peak O₂ [mean (SD), 144 (48) W]. Hyperventilation had a small effect on the calculation of mmol lactate buffered by HCO₃ ^– [6.5 (2.3)% at 6 min in four subjects who hyperventilated]. The mmol of buffer CO₂ at 6 min of exercise was highly correlated (r = 0.925, P < 0.001) with the increase in venous blood lactate sampled 2 min into recovery (coefficient of variation = ±0.9 mmol·l^–1). The reproducibility between tests done on different days was good. We conclude that the rate of release of CO₂2 from HCO₃ ^– can be estimated from the continuous analysis of simultaneously measured CO₂, O₂, and an estimate of muscle substrate.     

Distribution and air-water exchange of carbon dioxide in the Scheldt plume off the Belgian coast

In the present paper we report partial pressureof CO₂ (pCO₂) data obtained off theBelgian coast during 24 cruises. The temporaland spatial resolution of this data set allowsus to discuss satisfactorily seasonal andinter-annual variability of pCO₂ in thestudy area. The dynamics of pCO₂ aredescribed using two approaches: fixed referencestations and area survey cruises. The air-waterfluxes of CO₂ in the Scheldt estuarineplume and in the outer-plume region areestimated quantitatively, showing that theseareas correspond respectively to a net annualsource and sink of atmospheric CO₂. Theannually integrated air-water fluxes for theScheldt estuarine plume range between +1.1 and+1.9 mol m^–2 year^–1 as a function ofthe formulation of the exchange coefficient ofCO₂. The annual net emission of CO₂from the estuarine plume to the atmosphere isestimated to be between +2.3 to +4.0 Gmolyear^–1 which represents 17 to 29% of theestimate reported in the literature for the Scheldtinner estuary.     

Changes in the activity of the alternative oxidase in Orobanche seeds during conditioning and their possible physiological function

The appearance of the activity of the cyanide insensitive, alternative oxidase (AOX), pathway of oxygen uptake was followed in seeds of Orobanche aegyptiaca during conditioning. The pathway becomes operative during conditioning, up to day three as determined by inhibition of oxygen uptake of the seeds by propyl gallate. At the same time an increasing percentage of oxygen uptake is insensitive to cyanide and an increased oxygen uptake, responsive to propyl gallate, is induced by brief salicylic acid treatment of seeds. By day six of conditioning, these responses decrease and the AOX pathway could not be detected in germinating seeds, after treatment with a germination stimulant. These results were confirmed by following the reaction of extracts of fractions enriched with mitochondria from the conditioned seeds, using a specific antibody against AOX. Treatment of the seeds with inhibitors of AOX during conditioning significantly inhibited their subsequent germination. Addition of hydrogen peroxide after 4 and 7 days of conditioning resulted in reduced germination. In addition treatment of seed with propyl or octyl gallate during conditioning reduced the infection of tomato plants by Orobanche seeds and the development of tubercles of the parasite on the host roots. These results together indicate that the operation of AOX during conditioning has a significant function on the subsequent germination behaviour and pathogenicity of the root parasite. Some potential practical applications of these findings are discussed.     

Peroxidase catalysed formation of cytotoxic prooxidant phenothiazine free radicals at physiological pH

The antipsychotic phenothiazines may have other therapeutic applications because of their ability to kill bacteria, plasmids and tumor cells. They are also known to undergo a peroxidase-catalysed oxidation to form cation radicals that are stable at acid pH, but are not detected at a neutral pH. The objective of this project was to determine whether phenothiazine cation radical metabolites could cause oxidative stress at a neutral pH resulting in cytotoxicity. At a neutral pH, catalytic amounts of phenothiazines were found to be oxidised by a peroxidase/H2O2 system and also caused ascorbate, GSH and NADH cooxidation. NADH and GSH co-oxidation was accompanied by oxygen uptake and was increased by the addition of catalytic amounts of superoxide dismutase, indicating that the superoxide radical was formed. The phenothazines were different from other peroxidase substrates in that the NADH, ascorbate or GSH cooxidation was faster at pH 6.0 than pH 7.4, thereby partly reflecting the cation radical stability. The order of catalytic effectiveness found was promazine > chlorpromazine > trifluoperazine. Peroxidase/H2O2 also markedly increased phenothiazine cytotoxicity towards isolated rat hepatocytes at nontoxic phenothiazine concentrations. At both pH 6.0 and 7.4, the same order of phenothiazine catalytic effectiveness was observed as seen in the co-oxidation experiments. Cytotoxicity to hepatocytes could be attributed to oxidative stress as most hepatocyte glutathione oxidation and lipid peroxidation preceded phenothiazine induced cytotoxicity and that cytotoxicity was prevented by the antioxidant butylated hydroxyanisole. This hepatocyte/peroxidase/H2O2 system could be a useful model for studying drug induced idiosyncratic hepatic injury enhanced by inflammation.     

Open top chambers for exposing plant canopies to elevated CO2 concentration and for measuring net gas exchange

Open top chamber design and function are reviewed. All of the chambers described maintain CO₂ concentrations measured at a central location within ±30 ppm of a desired target when averaged over the growing season, but the spatial and temporal range within any chamber may be closer to 100 ppm. Compared with unchambered companion plots, open top chambers modify the microenvironment in the following ways: temperatures are increased up to 3°C depending on the chamber design and location of the measurement; light intensity is typically diminished by as much as 20%; wind velocity is lower and constant; and relative humidity is higher. The chamber environment may significantly alter plant growth when compared with unchambered controls, but the chamber effect on growth has not been clearly attributed to a single or even a few environmental factors.A method for modifying an open top chamber for tracking gas exchange between natural vegetation and the ambient air is described. This modification consists of the addition of a top with exit chimney to reduce dilution of chamber CO₂ by external ambient air, is quickly made and permits estimation of the effects of elevated CO₂ and water vapor exchange.The relatively simple design and construction of open top chambers make them the most likely method to be used in the near future for long-term elevated CO₂ exposure of small trees, crops and grassland ecosystems. Improvements in the basic geometry to improve control of temperature, reduce the variation of CO₂ concentrations, and increase the turbulence and wind speed in the canopy boundary layer are desirable objectives. Similarly, modifications for measuring water vapor and carbon dioxide gas exchange will extend the usefulness of open top chambers to include non-destructive monitoring of the responses of ecosystems to rising atmospheric CO₂.     

A model of the gas exchange response ofPicea abies to habitat conditions

Databases describing branch gas exchange ofPicea abies L. at two montane forest sites, Lägeren, Switzerland (National Forschungsprojekt 14 of the Schweizerische Nationalfonds) and Oberwarmensteinach, Germany (Bayerische Forschungsgruppe Forsttoxikologie), were analyzed in conjunction with a physiologically based model. Parameter estimates for describing carboxylase kinetics, electron transport, and stomatal function were derived, utilizing information from both single factor dependencies and diurnal time course measurements of gas exchange. Data subsets were used for testing the model at the branch level. Most of the observed variation in gas exchange characteristics can be explained with the model, while a number of systematic errors remain unexplained. Factors seen as contributing to the unexplained residual variation and not included in the model are light acclimation, degree of damage in adjustment to pollutant deposition, needle age, and cold stress effects. Nevertheless, a set of parameter values has been obtained for general application with spruce, e.g., for use in calculating canopy flux rates and to aid in planning of focused leaf and canopy level experiments. The value of the model for estimating fluxes between the forest and the atmosphere must be evaluated together with measurements at the stand level.     

Mass spectrometric determination of O2 gas exchange during a dark-to-light transition in higher-plant cells

The exchange of O₂ and CO₂ by photoautotrophic cells of Euphorbia characias L. was measured using a mass-spectrometry technique. During a dark-tolight transition the O₂ uptake rate was little affected whereas CO₂ efflux was decreased by 40%. In order to differentiate eventual superimposed O₂-uptake processes, the kinetics of O₂ exchange resulting from brief illuminations were measured with a highly sensitive device. When the cells were exposed to a saturating light for short periods, the rate of O₂ uptake passed through a series of transients: there was first a stimulation occurring 2–3 s after the appearance of O₂ from water-splitting, followed 30 s later by an inhibition. These two transients were reduced 80% by 3-(3,4-dichlorophenyl)1, 1-dimethylurea (DCMU), indicating that they relied on the linear transport of electrons in the chloroplasts. The first transient (stimulation of an O₂ uptake) was little affected by mitochondrial inhibitors such as antimycin A and oligomycin or the uncoupler carbonylcyanide m-chlorophenylhydrazone (CCCP) but was increased in presence of KCN. When spaced flashes (2 us duration; 100-ms intervals) were used instead of continuous light, this transient was almost suppressed indicating that it was dependent on the saturation of some component of the chloroplastic chain. The second transient (inhibition of O₂ uptake) was present when spaced flashes were used instead of continuous light. It was markedly decreased by addition of CCCP and mitochondrial inhibitors (antimycin A, oligomycin, KCN) which strongly indicates that it relied on mitochondrial respiration. It is concluded from these experiments that illumination of the cells resulted in an inhibition of mitochondrial respiration, but the resulting inhibition of O₂ uptake was hidden by the appearance of an O₂-uptake process of extramitochondrial origin, presumably located in the chloroplast.Abbreviations CCCP carbonylcyanide mchlorophenylhydrazone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - Rubisco ri-bulose-1,5-bisphosphate carboxylase/oxygenase The authors thank Drs A. Vermeglio, P. Thibault and P. Gans for helpful discussions.     

Pulmonary NO and CO2 uptake during pressure-induced lung expansion in rabbits

In artificially ventilated animals we investigated the dependence of the pulmonary diffusing capacities of nitric oxide (NO) and doubly 18O-labeled carbon dioxide (DLNO, DLC18O2) on lung expansion with respect to ventilator-driven increases in intrapulmonary pressure. For this purpose we applied computerized single-breath experiments to 11 anesthetized paralyzed rabbits (weight 2.8-3.8 kg) at various alveolar volumes (45-72 ml) by studying the almost entire inspiratory limb of the respective pressure/volume curves (intrapulmonary pressure: 6-27 cmH2O). The animals were ventilated with room air, employing a computerized ventilatory servo-system that we designed to maintain mechanical ventilation and to execute the particular lung function tests automatically. Each single-breath maneuver was started from residual volume (13.5+/-2 ml, mean+/-SD) by inflating the rabbit lungs with 35-55 ml indicator gas mixture containing 0.05% NO in N2 or 0.9% C18O2 in N2. Alveolar partial pressures of NO and C18O2 were measured by respiratory mass spectrometry. Values of DLNO and DLC18O2 ranged between 1.55 and 2.49 ml/(mmHg min) and 11.7 and 16.6 ml/(mmHg min), respectively. Linear regression analyses yielded a significant increase in DLNO with simultaneous increase in alveolar volume (P<0.005) and intrapulmonary pressure (P<0.023) whereas DLC18O2 was not improved. Our results suggest that the ventilator-driven lung expansion impaired the C18O2 blood uptake conductance, finally compensating for the beneficial effect of the increase in alveolar volume on DLC18O2 values.     

Activation/deactivation of acetylcholinesterase by H2O2: more evidence for oxidative stress in vitiligo

Previously it has been demonstrated that the human epidermis synthesises and degrades acetylcholine and expresses both muscarinic and nicotinic receptors. These cholinergic systems have been implicated in the development of the epidermal calcium gradient and differentiation in normal healthy skin. In vitiligo severe oxidative stress occurs in the epidermis of these patients with accumulation of H2O2 in the 10(-3)M range together with a decrease in catalase expression/activity due to deactivation of the enzyme active site. It was also shown that the entire recycling of the essential cofactor (6R)-l-erythro-5,6,7,8-tetrahydrobiopterin via pterin-4a-carbinolamine dehydratase (PCD) and dihydropteridine reductase (DHPR) is affected by H2O2 oxidation of Trp/Met residues in the enzyme structure leading to deactivation of these proteins. Using fluorescence immunohistochemistry we now show that epidermal H2O2 in vitiligo patients yields also almost absent epidermal acetylcholinesterase (AchE). A kinetic analysis using pure recombinant human AchE revealed that low concentrations of H2O2 (10(-6)M) activate this enzyme by increasing the Vmax>2-fold, meanwhile high concentrations of H2O2 (10(-3)M) inhibit the enzyme with a significant decrease in Vmax. This result was confirmed by fluorescence excitation spectroscopy following the Trp fluorescence at lambdamax 280nm. Molecular modelling based on the established 3D structure of human AchE supported that H2O2-mediated oxidation of Trp(432), Trp(435), and Met(436) moves and disorients the active site His(440) of the enzyme, leading to deactivation of the protein. To our knowledge these results identified for the first time H2O2 regulation of AchE. Moreover, it was shown that H2O2-mediated oxidation of AchE contributes significantly to the well-established oxidative stress in vitiligo.     

Carbon metabolism and gas exchange in leaves of Zea mays L.

The aim of this work was to investigate the mechanism of formation of triose phosphates and 3-phosphoglycerate during photosynthetic induction in leaves of Zea mays. Simultaneous measurements of gas exchange, chlorophyll a fluorescence and metabolite contents of maize leaves were made. Leaves illuminated in the absence of CO₂ showed a build-up of triose phosphates during the first 2 min of illumination which was comparable to the build-up observed in the presence of CO₂. Isolated mesophyll protoplasts, which lack the Calvin cycle, also showed a build-up of triose phosphates upon illumination. Leaves contained amounts of phosphoglycerate mutase and enolase adequate to account for the formation of triose phosphates and 3-phosphoglycerate from intermediates of the C₄ cycle and their precursors.     

Evaluation of H2O2 and pH in exhaled breath condensate samples: methodical and physiological aspects

Abstract

This veterinary study is aimed at further standardization of H₂O₂ and pH measurements in exhaled breath condensate (EBC). Data obtained in the study provide valuable information for many mammalian species including humans, and may help to avoid general pitfalls in interpretation of EBC data. EBC was sampled via the ‘ECoScreen’ in healthy calves (body weight 63–98 kg). Serum samples and condensates of ambient (indoor) air were collected in parallel. In the study on H₂O₂, concentrations of H₂O₂ in EBC, blood and ambient air were determined with the biosensor system ‘ECoCheck’. In EBC, the concentration of H₂O₂ was found to be dependent on food intake and increased significantly in the course of the day. Physiologically, lowest H₂O₂ concentrations at 06:00 varied within the range 138–624 nmol l^?1 EBC or 0.10–0.94 nmol per 100 l exhaled breath and individual concentrations were significantly different indicating a remarkable intersubject variability. Highly reproducible results were seen within each subject (three different days within 4 weeks). No correlation existed between H₂O₂ concentrations in EBC and blood, and EBC–H₂O₂ was not influenced by variables of spontaneous breathing. Further results confirmed that standardization of H₂O₂ measurements in EBC requires (1) the re-calculation of the concentration exhaled per 100 l exhaled breath (because the analyzed concentration in the liquid condensate underlies multiple methodological sources of variability given by the collection process), and (2) subtracting the concentration of inspired indoor H₂O₂. In the study on pH use of the ISFET electrode (Sentron, the Netherlands) and a blood gas analyzer ABL 550 (Radiometer, Denmark) led to comparable results for EBC–pH (r=0.89, R²=79.3%, p≤0.001). Physiological pH data in non-degassed EBC samples varied between 5.3 and 6.5, and were not significantly different between subjects, but were significantly higher in the evening compared with the morning. EBC–pH was not dependent on variables of spontaneous breathing pattern or ambient conditions, and no significant correlation was found between serum and EBC for pH.