Gas Exchange of Algae: II. Effects of Oxygen, Helium, and Argon on the Photosynthesis of Chlorella pyrenoidosa

Changes in the oxygen partial pressure of air over the range of 8 to 258 mm of Hg did not adversely affect the photosynthetic capacity of Chlorella pyrenoidosa. Gas exchange and growth measurements remained constant for 3-week periods and were similar to air controls (oxygen pressure of 160 mm of Hg). Oxygen partial pressures of 532 and 745 mm of Hg had an adverse effect on algal metabolism. Carbon dioxide consumption was 24% lower in the gas mixture containing oxygen at a pressure 532 mm of Hg than in the air control, and the growth rate was slightly reduced. Oxygen at a partial pressure of 745 mm of Hg decreased the photosynthetic rate 39% and the growth rate 37% over the corresponding rates in air. The lowered metabolic rates remained constant during 14 days of measurements, and the effect was reversible after this time. Substitution of helium or argon for the nitrogen in air had no effect on oxygen production, carbon dioxide consumption, or growth rate for 3-week periods. All measurements were made at a total pressure of 760 mm of Hg, and all gas mixtures were enriched with 2% carbon dioxide. Thus, the physiological functioning and reliability of a photosynthetic gas exchanger should not be adversely affected by: (i) oxygen partial pressures ranging from 8 to 258 mm of Hg; (ii) the use of pure oxygen at reduced total pressure (155 to 258 mm of Hg) unless pressure per se affects photosynthesis, or (iii) the inclusion of helium or argon in the gas environment (up to a partial pressure of 595 mm of Hg).     

CHANGES IN HEPATIC STRUCTURE IN RATS PRODUCED BY BREATHING PURE OXYGEN

The livers of rats exposed to pure oxygen were examined electron microscopically to study toxic effects of oxygen in a metabolically sensitive organ. Pressures of 1/3 (258 mm Hg), 1 (760 mm Hg), and 3 (2280 mm Hg) atmospheres were used, with exposures up to 90 days with the lowest pressures. The first changes in the hepatocytes were loss of glycogen and enlargement of mitochondria with development of mitochondria with bizarre shapes which were seen after 3 days at 258 mm, 1 day at 760 mm, and 3 hours at 2280 mm. These changes were followed by formation of increased numbers of cristae, membranes surrounding mitochondria, autophagic vacuoles, and polyribosome clusters. After 2 weeks at 258 mm, which is the pressure of the atmosphere of space cabins, numerous mitochondrial myelin figures appeared but the mitochondrial enlargement had begun to regress. After 90 days at 258 mm, the liver cells appeared almost normal except that many pigment granules had accumulated in the pericanalicular zones. The changes were non-specific and seemed to parallel biochemical alterations recorded elsewhere. They are not considered the result of toxicity but rather of adaptation. These atmospheres, which are used in clinical medicine and in space travel, appear to have no permanent deleterious effects on the liver in rats under the conditions of this experiment.     

Hyperbaria and stress

Performed on rats was study of the cause of appearance of stress reaction at action of hyperbaria upon organism. It was established that at the 5-h long action of gas mixtures (oxygen—nitrogen and oxygen—argon) under pressure of 0.35 and 0.5 MPa and partial pressure of oxygen of 0.02–0.03 MPa in camera 300 l in volume there was clearly realized stress confirmed by the corresponding markers. The appearance of stress was connected with density of gas mixture, which amounted to 6 g/l, that mechanically makes breathing difficult. On the other hand, use for respiration mixtures of elegas (SF6) with density of 6 g/l at normal pressure produces pronounced stress. At equal density, no difference was revealed in action of nitrogen, argon or elegas. Thus, use of high pressures requires light gases (helium, hydrogen, neon) that have low density.     

Effect of helium and argon on the oxygen uptake by lymphocytes

The effect of inert helium and argon gases on the tissue respiration has been studied on lymphocyte suspensions of white rats. It is shown that normoxic helium-oxygen mixture induces almost a two-fold increase of the O2 uptake by lymphocytes as compared with the control (air). No deviations in the value of the studied parameter are revealed in case of replacement of nitrogen from air by argon. Significance of the membrane structure in realization of effects of inert gases is under discussion.     

The secretion of inert gas into the swim-bladder of fish

The composition of the gas mixture secreted into the swim-bladders of several species of fish has been determined in the mass spectrometer. The secreted gas differed greatly from the gas mixture breathed by the fish in the relative proportions of the chemically inert gases, argon, neon, helium, and nitrogen. Relative to nitrogen the proportion of the very soluble argon was increased and the proportions of the much less soluble neon and helium decreased. The composition of the secreted gas approaches the composition of the gas mixture dissolved in the tissue fluid. A theory of inert gas secretion is proposed. It is suggested that oxygen gas is actively secreted and evolved in the form of minute bubbles, that inert gases diffuse into these bubbles, and that the bubbles are passed into the swim-bladder carrying with them inert gases. Coupled to a preferential reabsorption of oxygen from the swim-bladder this mechanism can achieve high tensions of inert gas in the swim-bladder. The accumulation of nearly pure nitrogen in the swim-bladder of goldfish (Carassius auratus) is accomplished by the secretion of an oxygen-rich gas mixture followed by the reabsorption of oxygen.     

Antiapoptotic activity of argon and xenon

Although chemically non-reactive, inert noble gases may influence multiple physiological and pathological processes via hitherto uncharacterized physical effects. Here we report a cell-based detection system for assessing the effects of pre-defined gas mixtures on the induction of apoptotic cell death. In this setting, the conventional atmosphere for cell culture was substituted with gas combinations, including the same amount of oxygen (20%) and carbon dioxide (5%) but 75% helium, neon, argon, krypton, or xenon instead of nitrogen. The replacement of nitrogen with noble gases per se had no effects on the viability of cultured human osteosarcoma cells in vitro. Conversely, argon and xenon (but not helium, neon, and krypton) significantly limited cell loss induced by the broad-spectrum tyrosine kinase inhibitor staurosporine, the DNA-damaging agent mitoxantrone and several mitochondrial toxins. Such cytoprotective effects were coupled to the maintenance of mitochondrial integrity, as demonstrated by means of a mitochondrial transmembrane potential-sensitive dye and by assessing the release of cytochrome c into the cytosol. In line with this notion, argon and xenon inhibited the apoptotic activation of caspase-3, as determined by immunofluorescence microscopy coupled to automated image analysis. The antiapoptotic activity of argon and xenon may explain their clinically relevant cytoprotective effects.     

Examination of the Role of NMDA and GABAA Receptors in the Effects of Hyperbaric Oxygen on Striatal Dopamine Levels in Rats

Hyperbaric oxygen induced in rats a decrease in striatal dopamine levels. Such decrease could be a result of changes in glutamatergic and GABAergic controls of the dopaminergic neurons into the Substantia Nigra Pars Compacta. The aim of this study was to determine the role of gluatamatergic and Gama-Amino-Butyric-Acid neurotransmissions in this alteration. Dopamine-sensitive electrodes were implanted into the striatum under general anesthesia. After one week rest, awaked rats were exposed to oxygen–nitrogen mixture at a partial pressure of oxygen of 3 absolute atmospheres. Dopamine level was monitored continuously (every 3 min) by in vivo voltammetry with multifiber carbon electrodes before and during hyperbaric oxygen exposure. Hyperbaric oxygen induced a decrease in dopamine level in relationship with the increase in partial pressure of oxygen (?40% at 3 ATA). The used of N-Methyl-d-Aspartate, agonist of glutamatergic N-Methyl-d-Aspartate receptors did not improve considerably this change and gabazine antagonist of Gama-Amino-Butyric-Acid-a receptors induced some little alteration of this change. These results suggest the involvement of other mechanisms.     

Neonatal intermittent hypoxia and hypertension

Obstructive apnea during sleep is accompanied by intermittent hypoxia (IH) leading to hypertension and other cardiovascular disturbances. A comparative evaluation of long-term effects of the neonatal IH on the cardiovascular functions was performed in normotensive Sprague-Dawley and spontaneously hypertensive rats (SHR). The newborn rats were placed for 30 days to conditions of IH (8% and 21% O₂, alternating every 90 s for 12 h/day). Control groups of rats were constantly kept in normoxia. By 6 months, in the spontaneously hypertensive rats exposed to IH at the period of wakefulness there was a statistically significant increase (as compared with control) of the systolic (185.8 ± 1.7 and 169.9 ± 1.4 mm Hg, correspondingly, p < 0.010 and the diastolic pressure (96.2 ± 4.9 and 86.0 ± 2.6 mm Hg, correspondingly, p < 0.01). During sleep, the systolic and diastolic pressure in these rats was higher than in control animals by 10 mm Hg (p < 0.01) and 12 mm Hg (p < 0.01), its decrease during sleep being absent. In SHR submitted to IH there was an increase in the power ratio of the heart rate variability from 0.9 ± 0.15 to 1.5 ± 0.17, which indicates a shift of the sympathico-parasympathetic balance in this group towards predominance of the sympathetic component. In the Sprague-Dawley rats exposed to neonatal hypoxia, the above-indicated changes were not prominent. These peculiarities of the hypertensive rats allow establishing connection of the genetic factor with the sympathetic mechanism providing long-term consequences of the neonatal IH for the cardiovascular control in the SHR.     

Effect of oxygen breathing on micro oxygen bubbles in nitrogen-depleted rat adipose tissue at sea level and 25 kPa altitude exposures

The standard treatment of altitude decompression sickness (aDCS) caused by nitrogen bubble formation is oxygen breathing and recompression. However, micro air bubbles (containing 79% nitrogen), injected into adipose tissue, grow and stabilize at 25 kPa regardless of continued oxygen breathing and the tissue nitrogen pressure. To quantify the contribution of oxygen to bubble growth at altitude, micro oxygen bubbles (containing 0% nitrogen) were injected into the adipose tissue of rats depleted from nitrogen by means of preoxygenation (fraction of inspired oxygen = 1.0; 100%) and the bubbles studied at 101.3 kPa (sea level) or at 25 kPa altitude exposures during continued oxygen breathing. In keeping with previous observations and bubble kinetic models, we hypothesize that oxygen breathing may contribute to oxygen bubble growth at altitude. Anesthetized rats were exposed to 3 h of oxygen prebreathing at 101.3 kPa (sea level). Micro oxygen bubbles of 500-800 nl were then injected into the exposed abdominal adipose tissue. The oxygen bubbles were studied for up to 3.5 h during continued oxygen breathing at either 101.3 or 25 kPa ambient pressures. At 101.3 kPa, all bubbles shrank consistently until they disappeared from view at a net disappearance rate (0.02 mm(2) × min(-1)) significantly faster than for similar bubbles at 25 kPa altitude (0.01 mm(2) × min(-1)). At 25 kPa, most bubbles initially grew for 2-40 min, after which they shrank and disappeared. Four bubbles did not disappear while at 25 kPa. The results support bubble kinetic models based on Fick's first law of diffusion, Boyles law, and the oxygen window effect, predicting that oxygen contributes more to bubble volume and growth during hypobaric conditions. As the effect of oxygen increases, the lower the ambient pressure. The results indicate that recompression is instrumental in the treatment of aDCS.     

Comparison of Nitrogen Narcosis and Helium Pressure Effects on Striatal Amino Acids: A Microdialysis Study in Rats

Exposure to nitrogen–oxygen mixture at high pressure induces narcosis, which can be considered as a first step toward general anaesthesia. Narcotic potencies of inert gases are attributed to their lipid solubility. Nitrogen narcosis induces cognitive and motor disturbances that occur from 0.3 MPa in man and from 1 MPa in rats. Neurochemical studies performed in rats up to 3 MPa have shown that nitrogen pressure decreases striatal dopamine release like argon, another inert gas, or nitrous oxide, an anaesthetic gas. Striatal dopamine release is under glutamatergic and other amino acid neurotransmission regulations. The aim of this work was to study the effects of nitrogen at 3 MPa on striatal amino acid levels and to compare to those of 3 MPa of helium which is not narcotic at this pressure, by using a new technique of microdialysis samples extraction under hyperbaric conditions, in freely moving rats. Amino acids were analysed by HPLC coupled to fluorimetric detection in order to appreciate glutamate, aspartate, glutamine and asparagine levels. Nitrogen–oxygen mixture exposure at 3 MPa decreased glutamate, glutamine and asparagine concentrations. In contrast, with helium–oxygen mixture, glutamate and aspartate levels were increased during the compression phase but not during the stay at maximal pressure. Comparison between nitrogen and helium highlighted the narcotic effects of nitrogen at pressure. As a matter of fact, nitrogen induces a reduction in glutamate and in other amino acids that could partly explain the decrease in striatal dopamine level as well as the motor and cognitive disturbances reported in nitrogen narcosis.     

Effects of Hyperbaric Oxygen at 1.25 Atmospheres Absolute with Normal Air on Macrophage Number and Infiltration during Rat Skeletal Muscle Regeneration

Use of mild hyperbaric oxygen less than 2 atmospheres absolute (2026.54 hPa) with normal air is emerging as a common complementary treatment for severe muscle injury. Although hyperbaric oxygen at over 2 atmospheres absolute with 100% O₂ promotes healing of skeletal muscle injury, it is not clear whether mild hyperbaric oxygen is equally effective. The purpose of the present study was to investigate the impact of hyperbaric oxygen at 1.25 atmospheres absolute (1266.59 hPa) with normal air on muscle regeneration. The tibialis anterior muscle of male Wistar rats was injured by injection of bupivacaine hydrochloride, and rats were randomly assigned to a hyperbaric oxygen experimental group or to a non-hyperbaric oxygen control group. Immediately after the injection, rats were exposed to hyperbaric oxygen, and the treatment was continued for 28 days. The cross-sectional area of centrally nucleated muscle fibers was significantly larger in rats exposed to hyperbaric oxygen than in controls 5 and 7 days after injury. The number of CD68- or CD68- and CD206-positive cells was significantly higher in rats exposed to hyperbaric oxygen than in controls 24 h after injury. Additionally, tumor necrosis factor-α and interleukin-10 mRNA expression levels were significantly higher in rats exposed to hyperbaric oxygen than in controls 24 h after injury. The number of Pax7- and MyoD- or MyoD- and myogenin-positive nuclei per mm² and the expression levels of these proteins were significantly higher in rats exposed to hyperbaric oxygen than in controls 5 days after injury. These results suggest that mild hyperbaric oxygen promotes skeletal muscle regeneration in the early phase after injury, possibly due to reduced hypoxic conditions leading to accelerated macrophage infiltration and phenotype transition. In conclusion, mild hyperbaric oxygen less than 2 atmospheres absolute with normal air is an appropriate support therapy for severe muscle injuries.     

Effects of fasting on maximum thermogenesis in temperature-acclimated rats

To further investigate the limiting effect of substrates on maximum thermogenesis in acute cold exposure, the present study examined the prevalence of this effect at different thermogenic capabilities consequent to cold- or warm-acclimation. Male Sprague-Dawley rats (n=11) were acclimated to 6, 16 and 26C, in succession, their thermogenic capabilities after each acclimation temperature were measured under helium-oxygen (21% oxygen, balance helium) at –10C after overnight fasting or feeding. Regardless of feeding conditions, both maximum and total heat production were significantly greater in 6>16>26C-acclimated conditions. In the fed state, the total heat production was significantly greater than that in the fasted state at all acclimating temperatures but the maximum thermogenesis was significant greater only in the 6 and 16C-acclimated states. The results indicate that the limiting effect of substrates on maximum and total thermogenesis is independent of the magnitude of thermogenic capability, suggesting a substrate-dependent component in restricting the effective expression of existing aerobic metabolic capability even under severe stress.     

Decompression sickness in the rat following a dive on trimix: recompression therapy with oxygen vs. heliox and oxygen.

Trimix (a mixture of helium, nitrogen, and oxygen) has been used in deep diving to reduce the risk of high-pressure nervous syndrome during compression and the time required for decompression at the end of the dive. There is no specific recompression treatment for decompression sickness (DCS) resulting from trimix diving. Our purpose was to validate a rat model of DCS on decompression from a trimix dive and to compare recompression treatment with oxygen and heliox (helium-oxygen). Rats were exposed to trimix in a hyperbaric chamber and tested for DCS while walking in a rotating wheel. We first established the experimental model, and then studied the effect of hyperbaric treatment on DCS: either hyperbaric oxygen (HBO) (1 h, 280 kPa oxygen) or heliox-HBO (0.5 h, 405 kPa heliox 50%-50% followed by 0.5 h, 280 kPa oxygen). Exposure to trimix was conducted at 1,110 kPa for 30 min, with a decompression rate of 100 kPa/min. Death and most DCS symptoms occurred during the 30-min period of walking. In contrast to humans, no permanent disability was found in the rats. Rats with a body mass of 100-150 g suffered no DCS. The risk of DCS in rats weighing 200-350 g increased linearly with body mass. Twenty-four hours after decompression, death rate was 40% in the control animals and zero in those treated immediately with HBO. When treatment was delayed by 5 min, death rate was 25 and 20% with HBO and heliox, respectively.     

Biochemical and metabolic effects of a six-month exposure of small animals to a helium-oxygen atmosphere

Rats and mice were exposed for periods of up to six months and two successive generations of mice were raised in a ground-level chamber system filled with 80% helium –20% oxygen, at 24°C. A duplicate chamber for controls contained a comparable nitrogen-oxygen mixture, and in both the other environmental parameters were well-controlled and nearly identical. Animals adapted to helium showed no greater increase in oxygen consumption (P>0.05) when placed in helium-oxygen than did those raised in air. Growth rates were identical, but the helium mice consumed more food and water.Selected biochemical analyses were made on the parent and two successive generations of mice. These included blood indices; electrophoretically separated tissue protein patterns from liver, skeletal muscle, and cardiac muscle; quantitative determinations of LDH, MDH, and G6PDH from the same tissues; serum insulin; and semi-quantitative histochemical estimates of liver glycogen. No cases of statistically significant difference or consistent trends were seen between the experimental environmental groups. Additional analyses of liver nucleotides and redox-coenzymes also failed to show a significant difference.The relative weights of liver, heart, kidney, and diaphragm (wet and dry) were the same in both groups. Histopathological examination of kidney and adrenal tissue produced unremarkable findings and none that were attributable to the nature of the gaseous environment.It must be concluded that prolonged exposure to helium-oxygen, relative to air, does not produce detectable changes in several key subcellular factors which might be altered by serious metabolic disturbances, and therefore the helium exposure is well tolerated.Prepared under Contract No. NAS 2-3900 for Union Carbide Corporation, Linde Division Research Laboratory, Tonawanda, N.Y. for Ames Research Center.     

Lactate dehydrogenase isoenzyme pattern and total LDH activity in the lung and liver of rats chronically exposed to low and high oxygen concentrations.

Young adult rats were continuously exposed for 44 and 84 days to environments containing 9–11%, 20%, and 80% oxygen. Low and high oxygen atmospheres were achieved by using boxes laminated with silicone rubber membranes which have a differing permeability for oxygen on one side and for carbon dioxide and nitrogen on the other. Animals exposed to both extreme concentrations significantly slowed body growth, and the weight of the lungs was proportionally less. The pattern of LDH isoenzymes in the lung showed the presence of all five characteristically changing isoenzymes in relation to oxygen concentration. A marked increase of M subunits in the LDH in lungs of rats exposed to low oxygen indicated a higher tissue concentration of lactate. Thus, the percentage of M subunits was significantly higher in low oxygen and significantly lower in lungs of rats exposed to high oxygen as compared to controls. Under the same experimental conditions there were no changes in the liver LDH isoenzyme pattern. Total LDH activity in the lungs of rats exposed to either extreme oxygen atmosphere was significantly elevated as compared to controls kept at an ambient atmosphere. It is concluded that chronic exposure of rats to low as well as to high oxygen was injurious to the lung tissue, as evidenced by total LDH activity. Thus, LDH isoenzyme pattern in the lung reflected the actual gas exposure (pO₂), rather than local tissue metabolism.     

Effect of High Oxygen Tension on Potassium Retentivity and Colony Formation of Bakers' Yeast

The ability of yeast cells to retain potassium and to form colonies was studied after exposure to pressures ranging from 2 to 143 atmospheres of oxygen. The investigations allow comparison of these responses with those found after x-ray exposure. Exposure to 2 to 8 atmospheres of oxygen for 2, 20, and 40 hours showed decreased potassium leakage as measured by an elution technique. Further experiments using 0.5 to 22 hour exposures to 10 to 143 atmospheres of oxygen showed decreased potassium leakage when glucose was present in the test media, but increased leakage (as did x-ray effects) in the absence of substrate. There was increased potassium leakage into the suspending media (distilled water) during oxygen exposure but this usually did not affect the leakage rates measured subsequently. Marked inability to form colonies was observed after 20 hour exposures to 100 atmospheres of oxygen, with a much smaller response at lower pressures. Increased oxygen concentrations, not pressure, evidently caused these effects, since comparable pressures of nitrogen produced almost no change. The ratio of potassium leakage to survival sensitivity was found to be approximately unity when comparing exposures causing 50 per cent damage. This is quite different from that seen with x-ray or ultraviolet irradiation.     

Effects of Various Gases on the Survival of Dried Bacteria During Storage

Salmonella newport and Pseudomonas fluorescens were dried together in papain digest broth and sucrose-glutamate, and stored in several gases at various water activities (a(w)) between 0.00 and 0.40 at 25 C for various periods up to 81 weeks. Both S. newport and P. fluorescens, dried in papain digest broth and stored in air, died rapidly if the conditions were very dry (0.00 a(w)) or moist (0.40 a(w)). Storage in carbon dioxide and argon gave greater survival than storage in air but lower survival than did storage in nitrogen or in vacuo. When the organisms were dried in a sucrose-glutamate mixture the differences between the gases were very small, and variations in residual water were less important. Of the inert gases, argon gave the best survival when the organisms were dried in papain digest broth, especially at 0.00 a(w); the survival in neon and krypton was lower and in xenon and helium it was much lower.     

Effect of replacement of air nitrogen by inert gases on oxygen consumption by the liver tissues in albino rats on various fatty diets

The effects of helium and argon, inert gases, on oxygen consumption have been studied on liver tissue of white rats who were delivered different fatty products plus to basic food). It is shown that the effects of helium and argon on the tissue respiration depend on the nature of fatty products. The role of membrane structure in realization of the influence of inert gases on tissue respiration is under discussion.     

Effect of exposure to high pressure on subsequent spatial learning and memory in rats

The effects of high helium pressure on the subsequent acquisition of spatial memory were studied in male rats. Thirty-two rats were exposed to 65 ATA helium-oxygen pressure for 4.2 days, decompressed (total time in chamber 5 days), and then tested in an eight-arm radial maze. Thirty-two control rats were exposed in the chamber to 1 ATA air. Each rat had 20 sessions in the maze (2 sessions/day for 10 days), and the number of correct (visiting an arm not previously visited to obtain the reward pellet) and incorrect choices (visiting a previously visited arm) were recorded. Statistical analysis showed that the rats exposed to 65 ATA performed significantly better than 1-ATA controls during the first 8 of 20 sessions. This effect was most pronounced in sessions 5-8. Results for sessions 9-20 showed that the pressure-treated rats still made more correct choices but to an extent that did not always reach statistical significance. Possible explanations include the pressure-treated rats performing better because of hunger after a lower food consumption at pressure. Alternatively, pressure itself may enhance proposed mechanisms of spatial memory such as long-term potentiation.     

Der Einfluß des Sauerstoffpartialdruckes und der Antibiotica Actinomycin und Puromycin auf das Wachstum,die Synthese von Bacteriochlorophyll und die Thylakoidmorphogenese in Dunkelkulturen von Rhodospirillum rubrum

Zusammenfassung Die Wachstumsrate (1/p; p = Proteinverdopplungszeit) von Rhodospirillum rubrum in aeroben Dunkelkulturen ist vom Sauerstoffpartialdruck abhängig. Das Optimum liegt bei 3–5 mm Hg [O₂]. Steigt die O₂-Konzentration auf 150 mm Hg [O₂] an, so vermindert sich die Wachstumsrate langsam um etwa 10%. Unterhalb 2 mm Hg fällt sie dagegen steil nach 0 ab. Die Ausbildung des gesamten Systems der Photophosphorylierung (Thylakoide, Chromatophoren) ist ein lichtunabhängiger, aber vom Sauerstoffpartialdruck direkt abhängiger Prozeß. Die Morphogenese wird induziert, wenn der Sauerstoffpartialdruck auf etwa 20 mm Hg erniedrigt wird. Das Optimum der Bacteriochlorophyll-bildung unter aeroben Dunkelbedingungen liegt bei etwa 2 mm Hg [O₂]. Die Pigmentsynthese kann durch Veränderung der Sauerstoffkonzentration induziert werden, ohne die Wachstumsgeschwindigkeit in der logarithmischen Wachstumsphase zu verändern. Eine Änderung der Wachstumsrate führt zu einer relativen Verschiebung der Syntheseraten für DNS, RNS und Protein.

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Summary The growth rate (1/p; p = time for protein doubling) of Rhodospirillum rubrum in aerobic dark cultures is dependent from the oxygen partial pressure. The optimum of growth is achieved at an oxygen partial pressure of 3 to 5 mm Hg. At 150 mm Hg [O₂] the growth rate will be reduced to 90% of the optimal rate. After lowering the oxygen partial pressure below 2 mm Hg the growth rate is dropped very strongly.The morphogenesis of the thylakoid-or chromatophore—membranes and the biosynthesis of bacteriochlorophyll are light independent processes. The morphogenesis is started by lowering the oxygen partial pressure. The optimum of bacteriochlorophyll synthesis in dark cultures is near the oxygen concentration of 2 mm Hg. It is possible to induce the pigment synthesis by lowering the oxygen partial pressure without changing the growth rate. But a change of the growth rate implies a change of the quotient protein/RNS and RNS/DNS. After induction of bacteriochorophyll synthesis early proteins are synthesized which are needed for the last part of the Mg-way of tetrapyrrol synthesis.

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Im Text verwendete Abkürzungen B.-Chlorophyll Bacteriochlorophyll - DNS Desoxyribonucleinsäure - RNS Ribonucleinsäure - ATP Adenosintriphosphat